DB3 GASTRULATION

Morphogensis

Achieved by gastrulation

Seperated into ectoderm, mesoderm, and endoderm

Ectoderm

Skin and nervous system

Mesoderm

Muscle, skeleton, blood, and kidney

Endoderm

Gut

Bottle cells

Surface cells change shape by restricting apical surface and fanning basal surface to create blastopore and move inside and under ectoderm and mesoderm

Archenteron

Primitive gut displaces blastocoel cavity

Convergent extension of the mesoderm

Presumptive mesoderm initially an equatorial ring but converges and extends along anteroposterior axis during gastrulation

Changes in cell shape and motility

Regulated by the cytoskeleton (actin-myosin)

Contractile ring - cleaving cell/cleavage

Contractile network

Lamellipodium - migrating cells

Contractile network

Organised contraction of cytoskeletal belt leading to apical constriction then to invagination

Cytoskeletal belt

Bundles of actin filaments connecting adjacent cells

Gastrulation in sea urchin

Primary mesenchymal cell formation → Invagination → Convergent extension by filopodium → Towing of archenteron→ Involution

Morphogenic maneuvers

Eating Ice Cream In Igloos May Induce Pneumonia

Epiboly

Intercalation

Convergent extension

Invagination

Involution

Migration

Ingression

Proliferation

Epiboly

Cells flatten and spread

Thinner cell layer with larger surface area

Increased cell-substratum adhesion

Intercalation

Cells intermix and spread out to form a single sheet

Changes in cell-cell adhesions

Convergent extension

Elongation of a tissue mass by extensive and concerted intercalation of cells

Changes in cell-cell and cell-substratum adhesion

Invagination

Localised areas of cell constriction cause buckling and bending of the sheet

Involution

Folding of the cell layer after invagination

Can be extensive

Migration

Cells move away (gain motility) from the edges of a coherent mass

Loss of cell-cell adhesion

Ingression

Cells detach from the epithelial layer and migrate (gain motility) into the basal ECM

Changes in cell-cell and cell-matrix adhesion

Proliferation

Cell multiplication expands the cell layer

Can lead to localised growth at an edge or folding and buckling

Spemann-Mangold Organiser

Only dorsal lip of blastopore is autonomouse (cell fate independent of positioning) and neighbouring cells are conditioned

Bottle cells communicate with cells to determine fate via a number of signalling molecules and their atagnonists initiating gastrulation

Nieuwkoop centre

Determines where gastrulation will start

30^o cortical rotation causes maternal factors in the egg to translocate directly opposite of fertilisation site and activate Wnt signalling (establishes a ß-catenin gradient) on dorsal side