doc-20190402-waaaaa0028-190407100309.pdf
- 1. MORPHOGENSIS “ It is the biological process that causes an organism to develop its shape.” MORPHOGENETIC MOVEMENTS; “During morphogenesis , individual cells or mass of cells move relative to each other. They fold, roll, bend , extend, spread and these movements are together called morphogenetic movement.”
- 2. CELLULAR PROCESS OF MORPHOGENESIS Cell intrinsic process 1. Cell division 2. Change in cell shape and size 3. Cell fusion 4. Cell death ( apoptosis ) Cell extrinsic process 5. Cell matrix interaction 6. Cell adhesion
- 3. 1. Role of cell division Cell division in morphogenesis involves two coordinated processes: 1. Growth ( differential cell proliferation results differential growth of some parts of embryo ) 2. Increase cell number ( number of cell increase by division of cell ) Cleavage determined by position and orientation of mitotic spindle.
- 4. 2. Change in cell shape and size Cell shape can be changed by reorganization of cytoskeleton. Change in size changes the volume. Changes in volume help cell to dilate in specific direction.
- 6. 3. Role of cell fusion Cell fusion is an important cellular process in which several uninuclear cells ( cells with a single nucleus ) combine to form a multinuclear cell, known as a syncytium. The first step of embryonic development ( fertilization ) is a process of cell fusion
- 7. Myoblasts ( undifferentiated proliferating cells ) aligned and form myotubes ( multi- nucleated fibers ). Actin and myosin ( muscle specific proteins ) are synthesized and then assembled into muscles fibers.
- 8. 4. Role of cell death Programmed cell division play role to generate the specific structure. Apoptosis ( cell death ) during limb development in vertebrates help in separation of digits .
- 9. 5. Role of cell-matrix interaction It is the material (or tissue) in animal or plant cells, in which more specialized structures are embedded. Matrix provides a substratum upon which cells can migrate. Many animal cells show extension migration individually or in group such as neural crest cells, germ cells etc. Loss of cell-matrix may result delamination of cells from its basal layers.
- 11. 6. Role of cell adhesion Cell adhesion is the process by which cells form contacts with each other through specialized protein complexes. It help the cells to organize into tissue and organs.
- 12. Cell adhesion molecules (CAM) bind animal cells together. These molecules determine whether some cells can adhere to some other cell or not. Gain in cell-cell adhesion results aggregation of cells. Loss of cell-cell adhesion results delamination of cells from an original layer.
- 13. Cell adhesion “Aggregation of cells following a genetic interaction and cells form tissues and organs is called the cell adhesion “ It is an important force in morphogenesis as well as morphogenesis movements. It is an organized making and breaking of cell contacts.
- 14. DIFFERENTIAL CELL AFFINITY Differential Cell Affinities is a dominant process that drives morphogenesis. In 1955 Towner and Holtfreter were the first to demonstrate differences in the cell surfaces of distinct cell types. Experiment: make single cell suspensions from different amphibian tissues soon after neural tube formation.
- 15. Using an alkaline solution, they made single cell suspensions from the ectoderm, endoderm and mesoderm layers of an embryo soon after neural tube formation. Two or more of the cell suspensions were combined. When the pH was normalized, cells formed aggregates on agar- coated petri dishes. Analysis of these aggregates demonstrated that: 1. Reaggregated cells become spatially segregated. Cells do not remain mixed. They sort out according to cell type.
- 17. 2. Typically, the final position of the reaggregated cells reflects their embryonic position. Holtfreter interpreted this as evidence for selective affinity. The inner surface of the ectoderm has a positive affinity for mesoderm and a negative affinity for endoderm. Mesoderm has positive affinity for both ectoderm and endoderm. 3. The selective affinity of cells changes during development.
- 19. On the basis of their sorting behavior in mixed aggregate, different types of cells can be given a rank according to their ability to occupy the central position. Example : Heart cells and liver cells are mixed , heart cells are always in the center surrounded by the liver cells. Again cartilage cells mixed with heart cells or liver cells, occupy the central position.
- 20. Tissues from chick form hierarchies of adhesiveness. a. When heart and liver cells are mixed ,heart cells take central position. b. When cartilage cells are mixed with liver or heart cells then cartilage cells take central position.
- 21. Differential adhesion hypothesis Differential adhesion hypothesis (DAH) is a hypothesis that explains cellular movement during morphogenesis with thermodynamic principles (closed system move naturally towards a state of minimum free energy). In DAH tissues are treated as liquids consisting of mobile cells whose varying degrees of surface adhesion cause them to reorganize spontaneously to minimize their interfacial free energy.
- 22. Steinberg in 1964 proposed that cells rearrange themselves into most thermodynamic stable pattern. Sorting of cells need difference in the strength of adhesion among those cell type. Cell types having greater surface tension sort within those cell types having lesser surface tension ( the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area ).
- 24. Cell adhesion molecules ( cam ) Cell adhesion molecules (CAMs) are a subset of cell adhesion proteins located on the cell surface involved in binding with other cells or with the extracellular matrix (ECM) in the process called cell adhesion. In essence, cell adhesion molecules help cells stick to each other and to their surroundings.
- 25. CAM is glycoprotein with three domains: Larger extracellular domain ( CAM-CAM ) Transmembrane domain ( CAM-plasma membrane ) Cytoplasmic domain ( microfilaments via linker protein )
- 26. Homophilic binding : CAM binds with same type of CAM. Heterophilic binding : Binding b/w different CAM. Binding specificity of CAM depend on protein and carbohydrate groups.
- 27. Cell-cell adhesion molecules 1. Cadherins ( Ca++ depending molecules ) 1. Immunoglobulin-like CAMs ( Ca++ independent molecules ) 1. Selection ( sugar adding process )
- 28. 1. cadherins Transmembrane proteins that mediate cell–cell adhesion in animals. ( homophilic ) It is a type of cell adhesion molecule (CAM) that is important in the formation of junctions to bind cells with each other. ( Ca++ depending ) Catenin: The complex protein that anchored the cadherins and form cadherin-catenin complex.
- 29. Cadherin-catenin-action interaction holds the cells together strongly.
- 30. 2. immunoglobulin-like CAM They are cell adhesion molecules that belong to Immunoglobulin superfamily of protein. ( antibodies ) They are either homophilic or heterophilic ( characterized by extracellular domains ). N-CAM (Neural Cell-Adhesion Molecule ) help in development of chicken retina, also stop connection b/w optic nerve and brain.
- 31. 3. selectins The selectins are a family of heterophilic CAMs that are depending on heterophilic mechanism ). Types of selectins: a. L-selectin (express on white blood cells) b. P-selectin (on platelets cells) c. E-selectin (on activated endothelial cells)