Animal Development

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Hypoblast

Endometrial epithelium (uterine lining)

Inner cell mass

Blastocoel

Uterus

Epiblast

Amniotic cavity

Expanding region of trophoblast

Yolk sac (from hypoblast)

Chorion (from trophoblast)

Extraembryonic mesoderm cells (from epiblast)

Slide 42

Morphogenesis in animals involves specific changes in cell shape, position, and adhesion

Morphogenesis is a major aspect of development in plants and animals.

Only in animals does it involve the movement of cells.

Slide 43

The Cytoskeleton, Cell Motility, and Convergent Extension

Changes in cell shape usually involve reorganization of the cytoskeleton.

Microtubules and microfilaments affect formation of the neural tube.

Slide 44

Change in cell shape during morphogenesis

Neural tube

Actin filaments

Microtubules

Ectoderm

Neural plate

Slide 45

The cytoskeleton also drives cell migration, or cell crawling, the active movement of cells.

In gastrulation, tissue invagination is caused by changes in cell shape and migration.

Cell crawling is involved in convergent extension, a morphogenetic movement in which cells of a tissue become narrower and longer.

Slide 46

Role of Cell Adhesion Molecules and the Extracellular Matrix

Cell adhesion molecules located on cell surfaces contribute to cell migration and stable tissue structure.

One class of cell-to-cell adhesion molecule is the cadherins, which are important in formation of the frog blastula.

Slide 47

Cadherin is required for development of the blastula

Control embryo

Embryo without EP cadherin

0.25 mm

0.25 mm

RESULTS

Slide 48

The developmental fate of cells depends on their history and on inductive signals

Cells in a multicellular organism share the same genome.

Differences in cell types is the result of differentiation, the expression of different genes = differential gene expression.

Slide 49

Two general principles underlie differentiation

1. During early cleavage divisions, embryonic cells must become different from one another.

If the egg’s cytoplasm is heterogenous, dividing cells vary in the cytoplasmic determinants they contain.

2. After cell asymmetries are set up, interactions among embryonic cells influence their fate, usually causing changes in gene expression