morphogenetic movements-developmental biology

morphogenetic movements in mammals and amphibians and morphogenesis

1. MORPHOGENETIC MOVEMENTS Done By : Steffy Thomas I MSc Biochemistry

2. INTRODUCTION In addition to the mechanism by which the complicated bodies of animals are formed via Cleavage of the fertilized egg and repeated cell specification, another important mechanism in animal development is morphogenetic movement . “ the movement of cells in the early embryo that change the shape or form of differentiating cells and tissues’’ is known as morphogenetic movement.

3. Morphogenetic movement occur in the embryo during : blastulation Gastrulation tubulation and Organogenesis They don't occur only during the embryonic stages , but also in adult animals which are reversible in nature while , the Morphogenetic movements of embryo is irreversible in nature i.e ., each part remains in the position into which it has been brought by the Preceding movements.

4. Morphogenetic movement is caused by large- scale and dynamic movement of embryonic cells. It rearranges the distribution of embryonic cells, thereby allowing the interaction between germ layers that previously existed separately.

5. The first morphogenetic movement triggered is gastrulation . Gastrulation is the one of the most important morphogenetic movements in the formation of the basic tubular structures of animals

6. Rearrangement of blastomeres to establish multilayered body plan by morphogenetic movements. Cells forming endodermal and mesodermal organs are brought inside Cells to form the ectoderm are spread over outside surface Cells are brought close enough together for inductive interactions

7. From a morphological point of view most embryonic cells can be regarded as epithelial or mesenchymal. Epithelia can arise from all three germ layers and mesenchyme from ectoderm and mesoderm. An epithelium is a sheet of cells, arranged on a basement membrane, each cell Joined to its neighbors by specialized junctions, and showing a distinct apical–basal polarity..

8. Mesenchyme is a descriptive term For scattered stellate cells embedded in loose extracellular matrix. It fills up much of the embryo and later forms fibroblasts, adipose tissue, smooth muscle, and skeletal tissues

9. The following are the two basic type of morphogenetic movement pattern are involved in gastrulation epiboly emboly Epiboly The word epiboly is derived from the Greek , meaning a “throwing on ” or extending upon.

10. Convergent extension A combination of processes that occurs during gastrulation resulting in cells converging i.e., sheets expands towards single point on the surface.

11. EPIAUXESIS Modified epibolic movement CONDITION: Absence of hyaline membrane Presence of a surface to which the blastomeres adheres and spreads Certain intracellular adhesion Mitotically active. Eg . Annelida and mollusca

12. Emboly This is just opposite to epiboly. In emboly sheets fold in or invaginate. Embolic movements involves: invagination involution Ingression or polyinvagination. delamination. Concrescence : the movement of masses of cells towards each other and their fusion into one cell mass. It occurs during the development of the feathers of birds.

13. The movement of individual cells (migration) INGRESSION ,EGRESSION the moment of individual cells into the embryo or out towards its surface DELAMINATION the movement of individual cells out of an epithelial sheet particularly when one epithelial sheet splits into two or more layers

14. INTERCALATION  the movement of individual cells into one epithelial sheet, particularly when two or more sheets merge into one   CONDENSATION A mesenchymal to epithelial transition where dispersed cells concrete to form an epithelium . DISPERSAL Epithelial to mesenchyme transition. When epithelial sheet breaks up to form dispersed mesenchyme cells

15. Movement of cells sheet in masses Invagination, evagination   The folding of a sheet of cells to form an indentation or protrusion. Invagination and evagination are essentially the same process, but in one case the sheet folds inwards and in other case The sheet folds out wards. Involution The inward turning of an expanding sheet of cells, so that the cells continue to spread over the internal surface of the sheet and create a second layer

16. Examples of morphogenetic movement in amphibians and mammalian embryos. The cells move in the directions of the red arrows shown in the diagram. a)Gastrulation of the frog embryo: the mesoderm and endoderm move into the interior of the embryo through invagination and extension movements and form an inner lining of the ectoderm

17. b) Gastrulation of the mammalian embryo: cells separate from the central part of the ectoderm and move into the interior of the embryo, and become endoderm and mesodermal cells. In the mammalian embryo, the archenteron is not actually formed at this time, but this morphogenetic movement is called gastrulation.

18. MECHANISM OF MORPHOGENESIS The developing embryo is dynamic and forms all manner of shapes and structures. This is achieved through various different types of cell behaviour. The term morphogenesis (creation of form) is used to describe how embryonic structures arise. Without morphogenesis , the embryo would never progress beyond a simple ball of cells and Dynamic processes such as gastrulation, embryonic folding and organogenesis would not be possible

19. The important morphogenetic processes are : Cell division Cell division influences morphogenesis in two ways: the rate of cell division contributes to differential growth in different parts of the embryo, eg : the selective growth of limb bud Such growth results from the secretion of growth factors firstly by the mesoderm itself and then by the apical ectodermal ridge overlying the limb bud .

20. Mesodermal- Ectodermal Interactions and the Role of Mesoderm in Limb morphogenesis Limb development occurs as the result of continuous interactions between the mesodermal and ectodermal components of the limb bud. The apical ectoderm stimulates outgrowth of the limb bud by promoting mitosis and preventing differentiation of the distal mesodermal cells of the limb bud.

21. Although the AER promotes outgrowth, its own existence is reciprocally controlled by the mesoderm. If an AER from an old limb bud is transplanted onto the mesoderm of a young wing bud, the limb grows normally until morphogenesis is complete. If old limb bud mesoderm is covered by young apical ectoderm, limb development ceases.

22. 2. the position and orientation of the mitotic spindle within the cell at cell division influences direction of cleavage ,the size and orientation of the daughter cells. Eg : In a single layer of epithelial cells division in the plane of the sheet will cause it t expand laterally, while division perpendicular t o the plane of the sheet will increase the number of the layer In plants , division within the plane of an epithelial sheet is known as anticlinal while perpendicular division are periclinal

23. During the cleavage stage of animal development, the orientation of the cleavage plane determines the relative size and organization of the blastomeres .

24. Cell size and shape changes in cell shape and size drive Mini folding and buckling movements such as those occurring during gastrulation and the formation of the neural tube. The shape of a cell can change by reorganization of the cytoskeleton and this can have profound effects on tissue structure.

25. In the developing vertebrate nervous system, the neural tube forms from the flat neural plate in part because the columnar cells of the plate constrict at the apical surface and become wedged shape , therefore helping to pull the two neural folds together. A similar process occurring in any epithelial sheet will make the sheet buckle (invaginate) The invagination of epithelial sheets occurs in many different developmental systems , and is particularly important during gastrulation in sea urchins and amphibians.

26. Cell size and shape can also change by varying volume. In animals for example , adipocytes grow in size as they accumulate storage lipids. In the developing leaf , cells can increase in size upto 50% by importing water into vacuoles . This can be used to dilate cells in a specific direction (directional dilation)

27. cell fusion cell fusion generates a multinucleated syncytium. This is important in the morphogenesis of developing muscle tissue and that of the trophectoderm during implantation in mammals.

28. programmed cell death programmed cell death by apoptosis in development is responsible for creating cavities such as the proamniotic cavity in Mouse development and gaps example between the digits in vertebrate limb development.

29. cell adhesion Tissue organization( transition between epithelial and mesenchyme cells, delamination, intercalation )occurs through changes in the pattern of cell adhesion molecules. The expression of different classes of cell adhesion molecules helps to keep like cells together in tissues and maintain boundaries between different issues.

30. The extracellular Matrix and cell migration The extracellular Matrix is a network of macromolecules secreted by cells into their local environment. Interactions between cells and the matrix can maintain epithelial sheets ,provide a substrate for and induce differentiation . The matrix is also the predominant component of some tissue, such as bone and cartilage

31. Morphogenetic process in development and examples from model developmental systems process examples Differential rates of cell proliferation selective out growth of vertebrate limb buds by proliferation of cells in the progress zone. Alternative positioning and orientation of mitotic spindle different embryonic cleavage patterns in animals Change of cell size cell expansion during leaf development in Arabidopsis. Change of cell shape change from columnar to wedge-shaped cells during neutral tube closure in birds and mammals . Cell fusion formation of trophoblast and myotubes in mammals.

32. Cell death separation of digits in vertebrate limb bud. Gain of cell-cell adhesion condensation of cartilage mesenchyme in vertebrate limb bud. Loss of cell-cell adhesion delamination of cells from epiblast during gastrulation in mammals Cell matrix interaction migration of neural crest cells and germ cells Loss of cell matrix adhesion delamination of cells from basal layer of the epidermis.

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