Principles of Animal Development

 ≈ 50% of protein-encoding genes in humans have recognisable homologues in Drosophila, C. elegans, and mice  Protein families involved in cell interactions and cell signalling frequently shared  Gene duplications in higher animals  more family members

Individual cells become more and more restricted in their development potential. This is accompanied by the acquisition of a specific gene expression pattern. Genes are switched on and off.

Cells become different according to their positions in the embryo. This means they must respond to the stimuli produced by other cells. • A group of cells might start with the same potential but then an extracellular signal induces one or more of the cells to change character. This is called Inductive Signalling.

A) Multiple signals concurring on one cell give rise to different cells  B) Cell memory (cells retain a record of what they have been and signals their ancestors have received) and therefore will respond to a stimulus based on this memory.

C) Different concentration of morphogen induce different gene expression patterns

Each cell can produce a substance x that acts on the other cell to inhibit the production of x. This is called lateral inhibition.

• Asymmetric Division : Sister cells born different 2. Symmetric Division : Sister cells become different as a result of difference’s on influences

The appropriate type of change  In the right place  Along body axis  Dorsal/ventral  Left/right  At the right time  Some molecular principles follow  Much more detail in Alberts, Ch 22 (on CD)

 Model organisms provide basic insights that extend to related organisms  C. elegans – worms  D. melanogaster – insects  M. musculus – mammals Both principles and molecular mechanisms are “re-used” across clades and at different stages of development