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14.6: Joints - Biology

14.6: Joints - Biology


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Double Jointed?

Is this person double jointed? No; there is no such thing, at least as far as humans are concerned. However, some people, like the individual pictured here, are much more flexible than others, generally because they have looser ligaments. Physicians call the condition joint hypermobility. Regardless of what it’s called, the feats of people with highly mobile joints can be quite impressive.

Figure (PageIndex{1}): Yoga

What Are Joints?

Joints are locations at which bones of the skeleton connect with one another. However, not all joints allow movement. Of joints that do allow movement, the extent, and direction of the movements they allow also vary.

Classification of Joints

Joints can be classified as structurally or functionally. The structural classification of joints depends on the manner in which the bones connect to each other. The functional classification of joints depends on the nature of the movement the joints allow. There is significant overlap between the two types of classifications because function depends largely on the structure.

Structural Classification of Joints

The structural classification of joints is based on the type of tissue that binds the bones to each other at the joint. There are three types of joints in the structural classification: fibrous, cartilaginous, and synovial joints.

  1. Fibrous joints are joints in which bones are joined by dense connective tissue that is rich in collagen fibers. These joints are also called sutures. The joints between bones of the cranium are fibrous joints.
  2. Cartilaginous joints are joints in which bones are joined by cartilage. The joints between most of the vertebrae in the spine are cartilaginous joints.
  3. Synovial joints are characterized by a fluid-filled space, called a synovial cavity, between the bones of the joints. You can see a drawing of a typical synovial joint in Figure (PageIndex{2}). The cavity is enclosed by a membrane and filled with a fluid, called the synovial fluid, which provides extra cushioning to the ends of the bones. Cartilage covers the articulating surfaces of the two bones, but the bones are actually held together by ligaments. The knee is a synovial joint.

Functional Classification of Joints

The functional classification of joints is based on the type and degree of movement that they allow. There are three types of joints in the functional classification: immovable, partly movable, and movable joints.

  1. Immovable joints allow little or no movement at the joint. Most immovable joints are fibrous joints. Besides the bones of the cranium, immovable joints include joints between the tibia and fibula in the lower leg and between the radius and ulna in the lower arm.
  2. Partly movable joints permit slight movement. Most partly movable joints are cartilaginous joints. Besides the joints between vertebrae, they include the joints between the ribs and sternum (breast bone).
  3. Movable joints allow bones to move freely. All movable joints are synovial joints. Besides the knee, they include the shoulder, hip, and elbow. Movable joints are the most common type of joints in the body.

Types of Movable Joints

Movable joints can be classified further according to the type of movement they allow. There are six classes of movable joints: pivot, hinge, saddle, plane, condyloid, and ball-and-socket joints. An example of each class, as well as the type of movement it allows, is shown in Figure (PageIndex{3}).

  • A pivot joint allows one bone to rotate around another. An example of a pivot joint is the joint between the first two vertebrae in the spine. This joint allows the head to rotate from left to right and back again.
  • A hinge joint allows back and forth movement like the hinge of a door. An example of a hinge joint is the elbow. This joint allows the arm to bend back and forth.
  • A saddle joint allows two different types of movement. An example of a saddle joint is the joint between the first metacarpal bone in the hand and one of the carpal bones in the wrist. This joint allows the thumb to move toward and away from the index finger and also to cross over the palm toward the little finger.
  • A plane joint also called a gliding joint, allows two bones that glide over one another. The joints between the tarsals in the ankles and between the carpals in the wrists are mainly gliding joints. In the wrist, this type of joint allows the hand to bend upward at the wrist and also to wave from side to side while the lower arm is held steady.
  • A condyloid joint is one in which an oval-shaped head on one bone moves in an elliptical cavity in another bone, allowing movement in all directions except rotation around an axis. The joint between the radius in the lower arm and carpal bones of the wrist is a condyloid joint as is the joint at the base of the index finger.
  • A ball-and-socket joint allows the greatest range of movement of any movable joint. It allows forward and backward as well as upward and downward motions. It also allows rotation in a circle. The hip and shoulder are the only two ball-and-socket joints in the human body.

Feature: My Human Body

Of all the parts of the skeletal system, the joints are generally the most fragile and subject to damage. If the cartilage that cushions bones at joints wears away, it does not grow back. Eventually, all of the cartilage may wear away. This is the cause of osteoarthritis, which can be both painful and debilitating. In serious cases, people may lose the ability to climb stairs, walk long distances, perform routine daily activities, or participate in activities they love such as gardening or playing sports. If you protect your joints, you can reduce your chances of joint damage, pain, and disability. If you already have joint damage, it is equally important to protect your joints and limit further damage. Follow these five tips:

  1. Maintain a normal, healthy weight. The higher your weight is, the more force you exert on your joints. When you walk, each knee has to bear a force equal to as much as six times your body weight. If a person weighs 200 pounds, each knee bears more than half a ton of weight with every step. Seven in ten knee replacement surgeries for osteoarthritis can be attributed to obesity.
  2. Avoid too much high-impact exercise. Examples of high-impact activities include volleyball, basketball, and tennis. These activities generally involve running or jumping on hard surfaces, which puts tremendous stress on weight-bearing joints, especially the knees. Replace some or all of your high-impact activities with low-impact activities, such as biking, swimming, yoga, or lifting light weights.
  3. Reduce your risk of injury. Don’t be a weekend warrior, sitting at a desk all week and then crowding all your physical activity into two days. Get involved in a regular, daily exercise routine that keeps your body fit and your muscles toned. Building up muscles will make your joints more stable and spread stress across them. Be sure to do some stretching every day to keep the muscles around joints flexible and less prone to injury.
  4. Distribute work over your body, and use your largest, strongest joints. Use your shoulder, elbow, and wrist to lift heavy objects, not just your fingers. Hold small items in the palm of your hand, rather than by the fingers. Carry heavy items in a backpack rather than in your hands. Hold weighty objects close to your body rather than at arms’ length. Lift with your hips and knees, not your back.
  5. Respect pain. If it hurts, stop doing it. Take a break from the activity at least until the pain stops. Try to use joints only to the point of mild fatigue, not pain.

Review

  1. What are the joints?
  2. What are the two ways that joints are commonly classified?
  3. How are joints classified structurally?
  4. Describe the functional classification of joints.
  5. How are movable joints classified?
  6. Name the six classes of movable joints, and describe how they move.
  7. Give an example of a joint in each of the classes of movable joints.
  8. True or False. The skull is one smooth bone and has no joints.
  9. True or False. A plane joint is a type of synovial joint.
  10. Which specific type of moveable joint do you think your knee joint is? Explain your reasoning.
  11. Explain the difference between cartilage in a cartilaginous joint and cartilage in a synovial joint.
  12. Why are fibrous joints immovable?
  13. Which type of joint has ligaments?
    1. Ball-and-socket
    2. Fibrous
    3. Cartilaginous
    4. None of the above
  14. Which type of joint allows for the greatest range of motion?
  15. What is the function of synovial fluid?

Explore More

Ehlers-Danlos syndrome is a group of inherited disorders that affect connective tissues. A relatively common form of the syndrome involves mainly the joints. People with this form of Ehlers-Danlos have overly flexible joints or joint hypermobility. This makes their joints prone to excessive wear and tear, dislocations, and early osteoarthritis. You can learn more about this disorder by watching these compelling videos:


Conservation and divergence of transcriptomic and epigenomic variation in maize hybrids

Recent genome-wide studies suggested that in addition to genetic variations, epigenetic variations may also be associated with differential gene expression and growth vigor in plant hybrids. Maize is an ideal model system for the study of epigenetic variations in hybrids given the significant heterotic performance, the well-known complexity of the genome, and the rich history in epigenetic studies. However, integrated comparative transcriptomic and epigenomic analyses in different organs of maize hybrids remain largely unexplored.

Results

Here, we generated integrated maps of transcriptomes and epigenomes of shoots and roots of two maize inbred lines and their reciprocal hybrids, and globally surveyed the epigenetic variations and their relationships with transcriptional divergence between different organs and genotypes. We observed that whereas histone modifications vary both between organs and between genotypes, DNA methylation patterns are more distinguishable between genotypes than between organs. Histone modifications were associated with transcriptomic divergence between organs and between hybrids and parents. Further, we show that genes up-regulated in both shoots and roots of hybrids were significantly enriched in the nucleosome assembly pathway. Interestingly, 22- and 24-nt siRNAs were shown to be derived from distinct transposable elements, and for different transposable elements in both shoots and roots, the differences in siRNA activity between hybrids and patents were primarily driven by different siRNA species.

Conclusions

These results suggest that despite variations in specific genes or genomic loci, similar mechanisms may account for the genome-wide epigenetic regulation of gene activity and transposon stability in different organs of maize hybrids.


Collection description

This collection (1930-2008, undated) contains materials documenting the work of George W. Beran and includes biographical information, research materials, and files related to his committee responsibilities for various organizations. The biographical information includes news clippings that discuss his time spent in the Philippines and the work he did there with the World Health Organization (WHO) and pseudorabies eradication. There are also newspaper articles written during his time as a professor at Iowa State that document awards he received as a professor and researcher.

An extensive portion of the collection is information regarding George Beran's work toward the eradication of pseudorabies. It includes quarterly and annual reports, committee meeting minutes, information from conferences, correspondence between Dr. Beran and others working to eliminate the disease, research regarding feral swine, newspaper and journal clippings, and research reports. In addition, there is information regarding pilot projects, including the project in Carroll County, Iowa, and reports and economic analyses from the research done at Iowa State University. There are descriptions of both the Iowa and national approaches to eradication.

In addition, the collection contains information from the American Veterinary Medical Association (AVMA), of which Beran was a member. These materials include biannual council meetings, documents from and correspondence with the American College of Preventive Medicine, and notes and information from the AVMA Food Safety Subcommittee.

There are several research reports and articles regarding food safety issues in the swine industry, food borne pathogens, and salmonella. Additionally, there are newspaper clippings and news releases from the Food Safety and Inspection Service, an organization with which Dr. Beran was involved throughout his career. There is also extensive information regarding the Hazard Analysis and Critical Control Point (HACCP) and the HACCP-Based Inspection Models Project (HIMP), including guides and documents, expense accounts, and visits and critiques of participating farms. Beran's research with e. coli. 0157:H7 is also included.


Life Cycle of Ustilago (With Diagram) | Fungi

According to the nuclear behaviour, the mycelium of Ustilago passes through two distinct stages of development. These are the primary and secondary mycelia.

The primary mycelium consists of hyaline, slender, septate hyphae with a single haploid(n) nucleus in each cell. This kind of mycelium is also called monokaryotic mycelium or haplomycelium.

It is formed by the germination of a basidiospore (fig. 14.2 A). It might be of a plus or a minus strain according as it is developed from a plus or a minus strain basidiospore.

It seldom develops very extensively. In most species the primary mycelium soon becomes converted into a secondary mycelium. The primary myeclium is thus of very short duration.

The secondary mycelium consists of hyphae with two haploid (n+n) nuclei in each cell. Such hyphae are called dikaryotic hyphae. These dikaryotic hyphae are septate and extensively branched.

The septa between the cells have each a central pore. The dolipore septal complex is, however, absent in the smuts. Through these pores the adjacent cells communicate with each other.

The mycelium of most species of Ustilago found within the host is generally dikaryotic or secondary

mycelium. It develops extensively within the tissues and spreads to the various parts of the host.

In fact the secondary mycelium constitutes the most conspicuous and important part of the somatic or vegetative phase of the majority of species of Ustilago. In many species, septa develop clamp connections.

The hyphae ramify in the spaces between the host cells. They are thus intercellular. The intercellular hyphae may develop distinct haustoria which penetrate the walls of the host cells and absorb nutrition.

The host cells, however, are not destroyed. In some species the haustoria are absent. In Ustilago maydis, the hyphae are intracellular. They penetrate the cells and obtain nutrition directly from the protoplasm of the host cells.

The growth of the parasitic mycelium within the host tissues causes little or no disturbance to the vegetative development of the host plant. In some species, the mycelium is scattered throughout the various parts of the host.

It is said to be systemic. In others it spreads near the point of infection and is called localised.

Dicaryotisation or Diploidisation in Ustilago:

The process whereby the primary mycelium produced by the germination of basidiospores changes into a secondary mycelium is called discaryotisation or diploidisation.

The process is ‘initiated by the pairing together of two haploid cells of opposite strains of a species. They copulate and one of them becomes binucleate.

The two nuclei in the fusion cell constitute a dicaryon. They do not fuse in the vegetative phase. The resultant dicaryotic or binucleate cell develops into a dicaryotic hypha which by further growth forms the dicaryotic or secondary mycelium. The formation of a dicaryotic cell is a prerequisite to normal infection in Ustilago.

In U. maydis (com smut) copulation to form the dicaryotic cell occurs inside the host tissue (com plant) but in all other species, in gereal, it occurs outside the host.

The various methods of diploidisation in Ustilago are detailed below:

1. By hyphal fusions (somatogamy) between primary mycelia (A). In U. maydis, the basidiospores or sporidia fall on the surface of the host (com plant) and germinate to produce haploid mycelia.

The latter penetrate the host epidermis and grow horizontally beneath. Dicaryotisation takes place within the host by means of hyphal fusions [somatogamy between hyphae of suitable mating (opposite) strains].

It may take place immediately after penetration within the host or after there has been some growth of primary mycelia. Subsequent migration of nuclei into the fusion cells initiates the dicaryotic phase.

Binucleate cells thus are formed by elongation and repeated cell division by clamp connections from the secondary mycelium.

2. By Fusion between the Germ Tubes of two germinating basidiospores (B-C). As the basidiospores germinate the germ tubes of the basidiospores of opposite strains meet and fuse.

The intervening walls at the point of corftact dissolve. The nucleus of one germ tube migrates into the other. The latter becomes binucleate. It grows into a secondary mycelium. Example of this type is U. hordei.

3. By Conjugation between the basidiospores. In some species the basidiospores multiply by budding to produce secondary spores (sporidia). The secondary spores or sprout cells of opposite strains (copulate).

The common wall between them dissolves at the point of contact or they send copulation tubes towards each other. The nucleus of one migrates into the other through the connecting link (I).

The binucleate sporidium, or sprout cell, on germination, produces the secondary mycelium. U. receptacularum and U. violocea are common examples.

4. By union of the basidiospores of one strain with the germ tube of the basidiospores of another strain.

5. By the union of infection threads. U. tritici is an example (H). The promycelium or basidium does not bear the basidiospores. Its haploid cells grow into small, slender hyphae one each. These are called the infection threads.

Two neighbouring infection threads of the opposite strains fuse. The nucleus of the one passes into the other. As a result one of the infection threads becomes binucleate. It grows to form the secondary mycelium.

Similarly in U. nuda fusion between the compatible cells of the epibasidium takes place by conjugation tubes (D). The conjugated binucleate cell forms a binucleated hypha which infects the host.

6. By fusion between the two haploid cells of the same epibasidium (E1, E2.) In this case fusion takes place between two haploid cells of opposite strains of the same basidium. U. hordei and U. carbo are the examples.

7. By fusion between two basidia formed by the germination of smut spores of opposite strains (G). U. nuda is an example.

8. In U. violacea the binucleate cell may arise by the union of a basidiospore with one of the basidial cells of the opposite strain (F).

Reproduction in Ustilago:

Sex organs are absent in Ustilago. Plasmogamy, karyogamy and meiosis, the three fundamental events of the sexual process do occur. Plasmogamy takes place by the fusion of two haploid compatible cells.

The binucleate cell thus formed by repeated divisions produces the secondary or dikaryotic mycelium. The intercellular hyphae of the latter feed on the host plant, accumulate reserve food materials and reaching a certain stage of development enter the sporulation stage.

1. Sporulation (Fig. 14.3):

In wheat, oat and barley, the invading secondary mycelium becomes active at the flowering time of the host. It grows vigorously and reaches the inflorescence region where it branches profusely and infects embryonic spikelets.

The parenchymatous tissue in the embryonic spikelets is destroyed and occupied by the hyphal masses. By the time, the head or ear emerges from the host leaf, it is generally completely destroyed (B).

Sporulation starts in the centre of the hyphal mass and progresses outwards as hyphal proliferation continues. The hyphae divide by additional septa into shorter binucleate segments called the spore fundaments.

These hyphae are called the sporogenous hyphae. They are closely interwined. The binculeate protoplast of each segment functions as the spore initial. The spore formation in Ustilago is thus endogenous and the sproes are formed singly inside the hyphal segments.

Sporulation is preceded by the thickening of the hyphal walls and their subsequent gelatinisation. The sporogenous hyphae thus lose their identity. The spore initials (binucleate cell protoplasts) lie in a hyaline, gelatinous matrix.

They are, at first, variously shaped but become globular as they enlarge. Each secretes a new wall around it to become a teliospore or brand spore. By the time the spores are morphologically mature, the gelatinous material disappears.

The spores are closely appressed into a hard, compact mass called a smut ball or sorus. The spores in the sorus are readily separable by slight pressure. The sorus or smut ball is covered by a peridium of host cells in U. hordei.

Virtually all the hyphae in hyphal mass are converted into spores after necrosis of the host tissues. No peridia or columellae of the fungal origin are formed. In U. hordei the group of spikelets at each node of the rachis forms a single irregularly shaped spore mass or sorus.

The differentiation and development of spores in other species of Ustilago such as U. avenae, U. tritici and U. nuda may closely follow the pattern of events described above in U. hordei.

The only difference is that in U. avenae and U. tritici, the fungal hyphae grow profusely between the anticlinal walls of the host epidermis and destroy the latter. The mature sori in these two species are thus naked, U. nuda with a growth pattern similar to U. hordei has the smut balls or sori enclosed in a fragile peridium derived from the host tissue.

The smuts in which the sori are covered by the membranous covering or peridium are called covered smuts. In loose smuts, the sori are naked. Each smut ball or sorus contains numerous, thick-walled, rounded spores. The thick spore wall is differentiated into two layers (D). The outer exine or exosporium is thick. It may be smooth, reticulate, or spiny. The inner intine or endosporium is always thin.

The binucleate smut spores are generally the resting spores. They remain dormant under adverse conditions. Some mycologists call the smut spores as teleutospore. The older mycologists termed them chlamydospores. The use of the term chlamydospores for the smut spores of Ustilago appears to be inappropriate.

The smut spores are binucleate structures produced only by the binucleate cells of the secondary mycelium which originates as a result of plasmogamy (sexual fusion). They are thus reproductive in nature and homologous to the teleutospores of rusts rather than to the chlamydospores.

The smut spores are dispersed by wind, insects, or washed by water. When all the spores are blown off small rachis are left behind on the infected ear. In U. tritici, the smut spores do not function as resting spores. They serve as means of propagating the disease during the growing season.

They fall on the stigmas of the flower and soon germinate to infect the ovules in the ovaries of the healthy plants. The spores of the covered smuts are liberated by the rupture of the walls of the grains at the threshing time.

2. Germination of smut spore to form the Basidium (Fig. 14.4).

This smut spores carried by the wind may fall on the soil, on the grain, and other favourable places. Under suitable conditions such as warmth and moisture they germinate.

Duran and Safeeulla (1968) reported that in most smuts optium temperature for smut spore germination ranges from 20 to 30°C. Light also stimulates smut spore germination. (ii) Karyogamy. Prior to germination the two nuclei (one of plus and the other of minus strain) in the smut spore fuse to form a synkaryon. It is diploid.

The thick-walled smut spore with a synkaryon represents the encysted probasidium or hypobasidium stage (A). It absorbs moisture and swells up. The exosporium or the epispore layer ruptures. The endospore or the endosporium protrudes in the form of a short, cylindrical hypha, the promycelium.

The promycelium is also called the epibasidium or metabasidium. (iii) Meiosis. The diploid nucleus migrates into the epibasidium and divides twice. These two divisions constitute meiosis (B) and (C). The resultant four nuclei in the epibasidium are thus haploid. Since segregation of the sexual strains takes place during meiosis two of these nuclei are of plus strain and two of minus strain.

They are arranged in a row (C). Septa are laid between the nuclei (D). The epibasidium at this stage is composed of four haploid cells.

The basidiospores of some species such as U. maydis are capable of multiplying by budding like the yeast cell (F). The new spores formed by budding are called secondary spores or conidia.

In U. tritici which parasitizes wheat the basidiospores are lacking. The haploid cells of the epibasidium or the promycelium, instead produce slender, short hyphae (Fig. 14.5 E). These are called the infection threads.

Germination of basidiospores and infection of the Host:

The basidiospores or the secondary sporidia produced from the them by budding germinate either on the soil or on the young host plant (U. maydis) itself. Each basidiospore produces a fine germ tube, also called the infection tube.

The germ tube is haploid (monokaryotic). In most speices it cannot infect the host tissues. Exception is U. maydis. Infection is generally brought about by the dikaryotic germ tube.

Dikaryotisation or diploidisation of the germ tubes if brought about differently in different species of Ustilago.

The following examples will illustrate the point:

It causes Covered smut of Barley. The basidiospores germinate in the soil or on barley grains as the latter are sown. The germ tubes produced by them are unable to bring about infection.

Diploidisation is brought about by fusion between the haploid germ tubes of the two basidiospores of opposite strains (Fig. 14.2 B-C). As a result one of the tubes becomes dikaryotic (binucleate).

The dikaryotic germ tube is capable of infecting the young barley seedling at a very early stage as it emerges from the grain. It gains entry into the host seedling through the hypocotyl and reaches the coleoptile.

U. hordei thus provides an example of infection at the seedling stage. Loose smut of Oats caused by U. avenae is also an example of infection at the seedling stage.

2. Ustilago tritici (Fig. 14.5):

The smut spores germinate on the feathery stigmas of the flower. Each produces a four celled promycelium or epibasidium (D). The cells of the epibasidium do not bear basidiospores.

Instead each basidium cell produces a slender tubular outgrowth, the infection thread (E). It is haploid. The infection threads of the same basidium with nuclei of opposite strains fuse to form a binucleate (dikaryotic) hypha (F).

The latter grows through the style until it reaches the ovary which it penetrates. In the ovary it ramifies in the intercellular spaces of the ovary tissue. By the tenth day of its origin it gains entry into the ovule.

It is an example of infection through the flower. The mycelium lies dormant in the grain (Fig, 14.6 A), and is again activated when the grain germinates (Fig. 14.6 B).

It spreads and grows along with the seedling (Fig. 14.6 C) till the latter matures and produces flower. The mycelium finally invades the ovaries (Fig. 14.6 D) and ovules.

Inside the ovaries it produces millions of smut spores which are exposed by the decay of host tissues. When the wind blows the spores are carried away leaving the naked rachis (Fig. 14.3 C).

3. Ustilago maydis (Com smut Fig. 14.4):

It is an example of general primary infection through many embryonic tissues of the host. The smut spores (teliospores) which are produced in summer are, at first, binucleate when young.

The two nuclei eventually fuse. The mature spores are thus uninucleate and diploid. They lie dormant in winter on com debris or other favourable places in the soil. They germinate in the following planting season of maize.

The thick spore wall ruptures. Through the split emerges a short cylindrical germ tube known as the promycelium or epibasidium. (A). Immediately the diploid nucleus migrates into the latter and undergoes meiosis (B-C).

The resultant four haploid nuclei are distributed uniformly and are arranged in a row. Septa are laid between the nuclei in the epibasidium (D). Each cell of the latter bears a haploid basidiospores.

The basidiospores are capable of budding. These basidiospores or the secondary basidiospores are carried by the wind. They happen to fall on a young com plant.

There each basidiospore germinates to produce a uninucleated germ tube (Fig. 14.2 A). It enters the host through a stoma or pierces the wall of the epidermal cell and brings about primary infection.

Infection can take place any time during the growing season and through any young and meristematic part of the host (stem, leaves, ears, tassels, etc.).

The haploid germ tubes from two basidiospores of plus and minus strain fuse in the tissue of the host and produce a binucleate cell (dikaryotic cell). This is diploidisation by somatogamy or somatogamous copulation (Fig. 14.2 A).

The resultant binucleate or dikaryotic cell grows by elongation and cell division by clamp connections to form a full-fledged secondary mycelium. The cells of the secondary mycelium (dikaryotic mycelium) are binucleate.

The secondary mycelium plays a dominant role and carries on the life cycle of the fungal parasite. It ramifies intercellularly and even intracellularly throughout the tissues of host.

It is reported that some of the hyphae of the secondary mycelium that reach the surface of the host, produce several crops of binucleate conidia during the growing season.

The mature binucleate conidia are dispersed by wind. Falling on the host the conidia initiate new or secondary infections. The disease spreads in this way. Eventually the secondary mycelium develops extensively at certain points.

At these points the extensive development of the mycelium causes swellings called galls or tumours (Fig. 14.8). These tumours can appear on any portion of the host e.g. stem, leaves, ears, tassels. Each swelling contains an indefinite number of smut spores.

Sexuality in Ustilago:

No sex organs are developed in Ustiiago. The sexual process is represented by three fundamental phenomena characteristic of it, namely, plasmogamy, karyogamy and meiosis.

(a) Plasmogamy (Fig. 14.2):

Heterothallism is common in the genus Ustiiago. The mycelia though morphologically alike are different physiologically. Physiologically they are unisexual. There is, however, no apparent distinction into male and female mycelia.

They are different only in their sexual behaviour. The difference of sex is thus very rudimentary. It is denoted by the signs plus and minus. Such mycelia are said to be heterothallic.

Plasmogamy in heterothallic species is brought about by different methods of diploidisation. It may be accomplished by conjugation between basidiospores of opposite strains (B-C).

Union may as well take place between a basidiospore of one strain and a cell of the basidium of opposite strain (F). There may be fusion between basidia of different smut spores (G).

Diploidisation is also brought about by somatogamous copulation between vegetative cells of the two hyphae of opposite strains. In either case a binucleate condition is established in one of the conjugating cells.

The binucleate cell is also called the dikaryotic cell. The dikaryotic condition once established is maintained for a considerable period in the life cycle. Plasmogamy therefore initiates dikaryophase in the life cycle.

The binucleate cell by elongation and division generally by clamp formation develops into a secondary mycelium.

With karyogamy the dikaryophase ends. The two nuclei in the smut spore fuse. This fusion between the two nuclei may be regraded as a culmination of the sexual process begun at the time of diploidisation. It is equivalent to the fertilisation process.

The diploid nucleus formed in this way is called a synkaryon. The smut spore with a synkaryon is the probasidium or hypobasidium. It represents the transitory diplophase in the life cycle of smuts.

The diploid smut spore germinates to form the promycelium or epibasidium. The synkaryon in the epibasidium undergoes meiosis to form four halpoid daughter nuclei.

The walls are laid between the nuclei. The epibasidium thus becomes a fourcelled structure. Each cell of the epibasidium bears a haploid basidiospore. With meiosis the transitory diplophase comes to an end in the life cylce of Ustilago.

Alternation of Generations in Ustilago:

The life cycle of Ustilago illustrates the important biological phenomenon of alternation of generations. There are two distinct phases in the life cycle.

The sexual phase or the gametophyte phase is represented by the haploid four-celled epibasidium, basidiospores, germ tubes of basidiospores and the haplo or primary mycelium in some species (U. maydis).

It ends with plasmogamy which initiates the dikaryophase in the life cycle. The dikaryophase in smuts consists of the dikaryotic or secondary mycelium and the binucleate smut spores.

With karyogamy which consists in the fusion of the two nuclei in the smut spore ends the dikaryotic phase. The smut spore with the synkaryon (probasidium) represents the transitory diplophase.

The dikaryotic phase together with the transitory diplophase consitutes the sporophyte phase. The sporophyte phase ends with meiosis. With meiosis starts the future gametophyte.

These two phases alternate with one another in the life cycle of Ustilago. One regularly follows the other. Hence Ustilago is said to exhibit alternation of generations in its life cycle.


Shota Atsumi

An increased understanding of system properties underlying cellular networks enables us to construct novel systems by assembling the components and the control systems into new combinations. We are applying this approach to the field of metabolic engineering, which strives for the optimization of desired properties and functions, such as the production of valuable biochemicals. The production of valuable chemicals from microorganisms suites to solve some significant challenges, such as converting renewable feedstocks into energy-rich biofuels. Currently, our main focus is developing synthetic organisms capable of converting CO2 directly to biofuels.

Grad Group Affiliations

  • Biochemistry, Molecular, Cellular and Developmental Biology
  • Chemistry
  • Microbiology
  • Plant Biology

Courses

  • CHE 105 Anal and Phys Chem Methods
  • CHE 135 Adv Bio-organic Chem Lab
  • CHE 237 Bio organic: Chemical Biology for Energy and Environment

Honors and Awards

Professional Societies

  • American Chemical Society
  • American Society for Microbiology
  • Society for industrial microbiology

Degrees

Publications

(56) Kobayashi, S., Nakajima, M., Asano, R., Ferreira, E.A., Abe, K., Tamagnini, P., Atsumi, S., and Sode, K.
Application of an engineered chromatic acclimation sensor for red-light-regulated gene expression in cyanobacteria
Algal Res 44: 101691 (2019) [Link]

(55) Gonzales, J.N., Matson M.M., Atsumi S.
Nonphotosynthetic Biological CO2 Reduction
Biochemistry 58: 1470-1477 (2019) [Pudmed]

(54) Tashiro, Y., Hirano, S., Matson, M.M., Atsumi, S*., Kondo, A*. *co-corresponding author
Electrical-biological hybrid system for CO2 reduction.
Metab Eng. 47: 211-218 (2018) [Pudmed]

(53) Carroll AL, Case AE, Zhang A, Atsumi S.
Metabolic engineering tools in model cyanobacteria.
Metab Eng. 50: 47-56 (2018) [Pudmed]

(52) M atson, M.M. & Atsumi, S.
Photomixotrophic chemical production in cyanobacteria
Curr Opin Biotechnol. 50: 65-71 (2018). [Pudmed]

(51) Zhang, A., Carroll, A.L., & Atsumi, S.
Carbon recycling by cyanobacteria: improving CO2-fixation through chemcial production
FEMS Microbiol Lett. 364: fnx165 (2017) [Pudmed]

(50) N ozzi, N.E., Case, A.E., Caroll, A.L. & Atsumi, S.
Systematic approaches to efficiently produce 2,3-butanediol in a marine cyanobacterium
ACS Synth Biol. 6: 2136-2144 (2017) [Pudmed]

(49) Kanno, M., Carroll, A.L. & Atsumi, S.
Global metabolic rewiring for improved CO2 fixation and chemical production in cyanobacteria
Nat Commun. 8: 14724 (2017) [Pudmed]
(highlighted in UCD Egghead)

(48) Kanno, M. & Atsumi, S.
Engineering an obligate photoautotrophic cyanobacterium to utilize glycerol for growth and chemical production
ACS Synth Biol. 6: 69-75 (2017) [Pudmed]
(highlighted in C&EN)

(47) Oliver, N.J., Ribinovitch-Deere, C.A., Carroll, A.L., Nozzi, N.E., Case, A.E., & Atsumi, S.
Cyanobacterial metabolic engineering for biofuel and chemical production
Curr Opin Chem Biol. 35: 43-50 (2016) [Pudmed]

(46) Desai, S.H., Koryakina, I., Case, A.E., Toney, M.D. & Atsumi, S.
Biological conversion of gaseous alkenes to liquid chemicals
Metab Eng. 38: 98-104 (2016) [Pudmed]

( 45) Case, A.E. & Atsumi, S.
Cyanobacterial chemical production
J Biotechnol. 231: 106-114 (2016) [Pudmed]

(44) M cEwen, J.T., Kanno, M. & Atsumi, S.
2,3 Butanediol production in an obligate photoautotrophic cyanobacterium in dark conditions via diverse sugar consumption
Metab Eng. 36: 28-36 (2016) [Pudmed]

(43) C arroll, A.L., Desai, S.H. & Atsumi, S.
Microbial production of scent and flavor compounds
Curr Opin Biotechnol. 37: 8-15 (2016) [Pudmed]

(42) Tashiro, Y., Desai, S.H. & Atsumi, S.
Two-dimensional isobutyl acetate production pathways to improve carbon yield
Nat Commun. 6: 7488 (2015) [Pudmed]

(41) Nozzi, N.E. & Atsumi, S.
Genome engineering of the 2,3-butanediol biosynthetic pathway for tight regulation in cyanobacteria
ACS Synth Biol. DOI: 10.1021/acssynbio.5b00057 (2015) [Pudmed]

(40) Desai, S.H., Rabinovitch-Deere, C.A., Fan, Z. & Atsumi, S.
Isobutanol production from cellobionic acid in Escherichia coli
Microb Cell Fact. 14: 52 (2015) [Pudmed]

(39) Oliver, J.W.K. & Atsumi, S.
A carbon sink pathway increases carbon productivity in cyanobacteria
Metab Eng. 29: 106-112 (2015) [Pudmed]

(38) Tashiro, Y., Rodriguez, G.M. & Atsumi, S.
2-Keto acids based biosynthesis pathways for renewable fuels and chemicals
J Ind Microbiol Biotechnol.42(3): 361-373 (2015) [Pudmed]

(37) Rodriguez, G.M. & Atsumi, S.
Toward aldehyde and alkane production by removing aldehyde reductase activity in Escherichia coli
Metab Eng. 25: 227-237 (2014) [Pudmed]

(36) Nozzi, N.E., Desai, S.H., Case, A.N., & Atsumi, S.
Metabolic engineering for Higher alcohol produciton
Metab Eng. 25: 174-182 (2014) [ Pudmed ]

(35) McEwen, J.T. & Atsumi, S.
Engineering trophic diversity into photosynthetic microbes
Biofuels 5(3): 199-201 (2014) [ Link ]

(34) Oliver, J.W.K. & Atsumi, S.
Metabolic design for cyanobacterial chemical synthesis
Photosynth Res. 120(3): 249-261 (2014) [ Pudmed ]

(33) Rodriguez, G.M.*, Tashiro, Y.*, & Atsumi, S. Expanding ester biosynthesis in Escherichia coli Nat Chem Biol. 10: 259-265 (2014) *Contributed equally to this work

(32) Oliver, J.W.K.*, Machado, I.M.P.*, Yoneda, H., & Atsumi, S. Combinatorial optimization of cyanobacterial 2,3-butanediol production Metab Eng. 22: 76-82 (2014) *Contributed equally to this work

(31) Desai, S.H., Rabinovitch-Deere, C.A., Tashiro, Y., & Atsumi, S. Isobutanol production from cellobiose in Escherichia coli Appl Microbiol Biotechnol. 98(8): 3727-3736 (2014)

(30) Kusakabe, T., Tatsuke, T., Tsuruno, K., Hirokawa, Y., Atsumi, S., Liao, J.C., & Hanai, T. Engineering a synthetic pathway in cyanobacteria for isopropanol production directly from carbon dioxide and light Metab. Eng. 20: 101-108 (2013)

(29) Yoneda, H., Tantillo, D.J., & Atsumi, S. Biological production of 2-butanone in Escherichia coli ChemSusChem 7(1): 92-95. (2014)

(28) Nozzi, N.E., Oliver, J.W.K. & Atsumi, S. Photosynthetic approaches to chemical biotechnology Front. Bioeng. Biotechnol. 1:7. (2013)

(27) Desai, S.H. & Atsumi, S. Photosynthetic approaches to chemical biotechnology Curr Opin Biotechnol. 14(6): 1031-1036 (2013)

(26) Rabinovitch-Deere, C.A., Oliver, J.W.K, Rodriguez, G.M., & Atsumi, S. Synthetic Biology and Metabolic Engineering Approaches to Produce Biofuels Chem Rev. 113(7): 4611-4632 (2013)

(25) McEwen, J.T., Machado, I.M.P, Connor, M.R., & Atsumi, S. Engineering Synechococcus elongatus PCC 7942 to grow continuously in diurnal conditions Appl Environ Microbiol. 79(5):1668-1675 (2013)

(24) Oliver, J.W.K.*, Machado, I.M.P.*, Yoneda, H., & Atsumi, S. Cyanobacterial conversion of carbon dioxideto 2,3-butanediol Proc. Natl. Acad. Sci. USA 110(4): 1249-1254 (2013) *Contributed equally to this work

(23) Rodriguez, G.M. & Atsumi, S. Isobutyraldehyde production from Escherichia coli by removing aldehyde reductase activity Microbial Cell Factories 11:90 (2012)

(22) Lamsen, E.N. & Atsumi, S. Recent progress in synthetic biology for microbialproduction of C3–C10 alcohols Frontiers in Microbiology 3:196 (2012)

(21) Machado, I.M.P. & Atsumi, S. Cyanobacterial biofuel production J Biotechnol 162: 50-56 (2012)

(20) Rodriguez, G.M. & Atsumi, S. Synthetic biology approaches to produce C3-C6 alcohols from microorganisms Curr Chem Biol 6: 32-41 (2012)

(19) McEwen, J.T. & Atsumi, S. Alternative biofuel production in non-natural hosts Curr Opin Biotechnol. 23: 744-750 (2012)

(18) Atsumi, S.*, Wu, T.*, Machado, I.M.P., Huang, W., Chen, P., Pellegrini, M. & Liao, J.C. Evolution, genomic analysis, and reconstruction of isobutanol tolerance in Escherichia coli Mol Syst Biol. 6: 449 (2010) Contributed equally to this work

(17) Connor, M.R. & Atsumi, S. Synthetic Biology Guides Biofuel Production J Biomed Biotechnol. 2010:541698 doi: 10.1155/2010/541698 (2010)

(16) Wong, I., Atsumi, S., Huang, W., Wu, T., Hanai, T., Lam, M., Tang, P., Yang, J., Liao, J.C. & Ho, C. An agar gel membrane-PDMS hybrid microfluidic device for long term single cell dynamic study Lab Chip 10: 2710-2719 (2010)

(15) Atsumi, S., Higashide, W. & Liao, J.C. Direct recycling of carbon dioxide to isobutyraldehyde using photosynthesis Nat Biotechnol. 27: 1177-1180 (2009)

(14) Atsumi, S., Li, Z. & Liao, J.C. Acetolactate synthase from Bacillus subtilis serves as a 2-ketoisovalerate decarboxylase for isobutanol biosynthesis in Escherichia coli Appl Environ Microbiol. 75: 6306-6311 (2009)

(13) Atsumi, S., Wu, T., Eckl, E., Hawkins, S.D., Buelter, T. & Liao, J.C. Engineering the isobutanol biosynthetic pathway in Escherichia coli by comparison of three aldehyde reductase/alcohol dehydrogenase genes Appl Microbiol Biotechnol. 85:651-657. (2010)

(12) Atsumi, S. & Liao, J.C. Directed evolution of thermophilic citramalate synthase for 1-propanol and 1-butanol biosynthesis from Escherichia coli Appl Environ Microbiol. 74: 7802-7808 (2008)

(11) Atsumi, S. & Liao, J.C. Metabolic Engineering for Advanced Biofuels Production from Escherichia coli Curr Opin Biotechnol. 19: 414-419 (2008)

(10) Atsumi, S., Hanai, T. & Liao, J.C. Non-Fermentative Pathways for Synthesis of Branched-Chain Higher Alcohols as Biofuels Nature 451: 86-89 (2008)

(9) Hanai, T., Atsumi, S. & Liao, J.C. Engineered synthetic pathway for isopropanol production in Escherichia coli Appl Environ Microbiol. 73: 7814-7818 (2007)

(8) Atsumi, S., Can, A.F., Connor, M.R., Shen, C.R., Smith, K.M., Brynildsen, M.P., Chou, K.J., Hanai, T & Liao, J.C. Metabolic engineering of Escherichia coli for 1-butanol production Metab. Eng. 10: 305–311 (2008)

(7) Atsumi, S. & Little, J.W. A synthetic phage lambda regulatory circuit Proc. Natl. Acad. Sci. USA. 103: 19045-19050 (2006)

(6) Atsumi, S. & Little, J.W. Role of the lytic repressor in prophage induction of phage lambda analyzed by a module-replacement approach Proc. Natl. Acad. Sci. USA. 103: 4558-4563 (2006)

(5) Atsumi, S. & Little, J.W. Regulatory circuit design and evolution using phage lambda Genes Dev 18: 2086-2094 (2004)

(4) Ikawa, Y., Tsuda, K., Matsumura, S., Atsumi, S. & Inoue, T. Putative intermediary stages for the molecular evolution from a ribozyme to a catalytic RNP Nucleic Acids Res 31: 1488-1496 (2003)

(3) Atsumi, S., Ikawa, Y., Shiraishi, H. & Inoue, T. Selections for constituting new RNA-protein interactions in catalytic RNP Nucleic Acids Res, 31: 661-669 (2003)

(2) Atsumi, S., Ikawa, Y., Shiraishi, H. & Inoue, T. Design and development of a catalytic ribonucleoprotein EMBO.J, 20: 5453-5460 (2001)

(1) Ikawa, Y., Nohmi, K., Atsumi, S., Shiraishi, H. & Inoue, T. A comparative study on two GNRA-tetraloop receptors: 11-nt and IC3 motif J. Biochem. (Tokyo) 130: 251-255 (2001)


Career Prospects

  • Geological knowledge is required for the construction of airports, buildings, tunnels, bridges, dams, ports, power stations, reclamations and landfills, and for dealing with natural hazards such as earthquakes and landslides. Currently, geologists are in demand worldwide to ensure essential supplies of water, oil, minerals and raw materials
  • Graduates are trained to fill a variety of positions, or to undertake further specialised training programmes either in universities or through government/industry initiatives. They are competent to work in the mining industry, hydrogeology, environmental geology and the management of natural hazards
  • Given the demands imposed by large-scale construction projects and the pressures for better environmental management, the need for geologists is likely to continue. In recent years, a number of our graduates have been employed by resource development and mining companies in Canada, Brazil, Australia and Mainland China
  • There is a strong demand for geologists in the local geotechnical profession. Major geotechnical projects involving site formation works, foundation construction, and tunnelling and slope safety management all require people with a strong geological backgrounds.

The wide portion of the long bone between the narrow diaphysis and the epiphysis that grows during childhood.

This is the organic un-mineralized portion of the bone matrix composed primarily of type I collagen that is secreted by osteoblasts prior to maturation of bone tissue.

Conventional osteosarcomas are primary intramedullary high-grade malignant tumours in which neoplastic cells produce osteoid.

Low-grade central osteosarcomas arise from the medullary cavity of bone and are composed of hypo-cellular to moderately cellular fibroblastic stroma with variable amounts of osteoid.

Periosteal osteosarcoma is an intermediate-grade chondroblastic osteosarcoma that occurs on the surface of the metaphysis of long bone.

Parosteal osteosarcoma is a low-grade tumour that originates from the outer surface of the periosteum.

Telangiectatic osteosarcoma occurs in the metaphyseal portion of the long bones. It is characterized by dilated blood-filled vascular spaces lined by malignant osteoblasts.

In chondroblastic osteosarcoma, chondroid matrix is predominant, with minimal amounts of osseous matrix.

Small cell osteosarcoma is composed of small cells with variable degrees of osteoid production.

Thick membranes composed of fibrous connective tissue that wraps around all bone except for the articulating surfaces in joints.

Alternative lengthening of telomeres

(ALT). A mechanism used by 10–15% of cancer cells to counteract telomere attrition that accompanies DNA replication and finite replicative potential. ALT uses homologous recombination to maintain telomere length throughout many cell doublings in the absence of telomerase activity.

A genomic phenomenon in which a single catastrophic event results in massive genomic rearrangements and remodelling of a chromosome.

Kataegis is defined by patterns of localized hypermutation colocalized with regions of somatic genome rearrangements.

Quality-adjusted life years

This measure takes into account both the quantity (life expectancy) and the quality of the remaining life years generated by health care interventions.

Chimeric antigen receptors

(CARs). These are engineered receptors that consist of an antibody-derived targeting domain fused with a T cell signalling domain that, when expressed by T cells, confers T cell antigen specificity governed by the targeting domain of the CAR.

Keyhole limpet haemocyanin

(KLH). This is a large, multi-subunit metalloprotein that is found in the haemolymph of the giant keyhole limpet (Megathura crenulata), which is a type of gastropod, and is used extensively as a carrier protein to generate a substantial immune response in the production of antibodies.


Antagonistic Smads in feedback and crosstalk

In addition to R-Smads and co-Smads, which carry signals from receptors to the nucleus, a third group of Smads act antagonistically, abrogating TGF-β signal transduction. The antagonistic Smads include Smad6 and Smad7 in vertebrates, Dad in Drosophila, and possibly Daf-3 in Caenorhabditis elegans. They contain a carboxy-terminal MH2 domain but have very little similarity to a cannonical MH1 domain in the amino-terminal region. The antagonistic Smads are known to mediate negative feedback within TGF-β signaling pathways and regulatory inputs from other pathways.

Smad7 inhibits Smad phosphorylation by occupying type I receptors for TGF-β, Activin, and BMP (for review, see Heldin et al. 1997Massagué 1998) (Fig. 6). Mouse Smad7 preferentially inhibits Activin and TGF-β signaling over BMP signaling (Souchelnytskyi et al. 1998 Ishisaki et al. 1999). The reverse is true of aXenopus Smad7 homolog (Souchelnytskyi et al. 1998). Smad7 appears to reside predominantly in the nucleus at basal state and translocates to the cytoplasm upon TGF-β stimulation (Itoh et al. 1998). The significance of this phenomenon remains to be elucidated.

Smad6 preferentially inhibits BMP signaling by a mechanism different from that of Smad7 (Hata et al. 1998 Ishisaki et al. 1999). When expressed at levels that are sufficient for inhibition of BMP signaling but not TGF-β signaling, Smad6 does not interfere with receptor function but competes with Smad4 for binding to receptor-activated Smad1 and yields inactive Smad1–Smad6 complexes (Fig. 6). Overexpression of Smad4 can outcompete Smad6 and rescue BMP signaling (Hata et al. 1998). At higher expression levels, Smad6 can mimic Smad7 and inhibit signaling by BMP and TGF-β receptors (Imamura et al. 1997). Smad6-defective mice have multiple defects in the development and homeostasis of the cardiovascular system (Galvin et al. 2000). The ossification of the aorta in these animals, in particular, is suggestive of an excess of BMP signaling activity.Drosophila Dad antagonizes Dpp signaling in the control of anteroposterior patterning of the wing imaginal disc (Tsuneizumi et al. 1997).

The expression of both Smad6 and Smad7 is increased in response to BMP, Activin and TGF-β, suggesting roles in negative feedback of these pathways (Nakao et al. 1997 Ishisaki et al. 1998, 1999) (Fig. 7).Smad6 expression in the developing chick heart can be diminished by ectopic Noggin and augmented by ectopic BMP2, suggesting that a BMP negative feedback loop via Smad6 has a role in orchestrating BMP-mediated cardiac development (Yamada et al. 1999). Similarly, Dpp induces the expression of its own antagonist Dad in Drosophila(Tsuneizumi et al. 1997).

The expression of Smad7 can also be increased by pathways that negatively regulate TGF-β signaling (Fig. 7). One example is provided by the ability of interferon-γ (IFN-γ), acting via the Jak1 tyrosine kinase and the Stat1 transcription factor, to increase Smad7 expression (Ulloa et al. 1999). As a result, IFN-γ inhibits TGF-β-mediated Smad3 phosphorylation and signal transduction. Thus, Smad7 induction by IFN-γ provides a mechanism for transmodulation between the STAT and SMAD signal-transduction pathways, providing a basis for the known antagonism between TGF-β and IFN-γ in the regulation of immune cell functions. A similar set of events has been shown to occur in response to the proinflammatory cytokines tumor necrosis factor-α and interleukin-1β, which activateSmad7 expression via the NF-κB/RelA transcription factor (Bitzer et al. 2000).


Tissue-Engineering Heart Valves

Mark W. Maxfield , . Christopher K. Breuer , in Principles of Tissue Engineering (Fourth Edition) , 2014

Conclusion

Successful development of a tissue-engineered replacement heart valve holds the key to better treatment and improved clinical outcomes for end-stage valvular disease. Although significant progress has been achieved since its inception in the early 1990s, the field is young and many key issues have yet to be resolved. We are still exploring the cellular and ECM biology that govern the maintenance of a normal valve. Better characterization of valve cells like VECs and VICs may offer clues to optimize cell seeding. Moreover, advances in other fields of tissue engineering and stem cell biology may provide new techniques and cell types that could transform either the cell source or cell seeding technique used in engineered heart valves. Similarly, growth in other fields like 3D printing or quantification of flow using magnetic resonance imaging may eventually find clinical applications of their respective technologic advancements in engineering heart valves. To that point, it is clear that tissue engineering is a multi-disciplinary, multi-faceted field that requires cooperation, coordination, and collaboration between experts in a variety of different specialties. Fostering these types of relationships using unique funding mechanisms and programs will help move this field forward and will ultimately benefit tissue engineering as a field and the patients that benefit from its growth.


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