Evo-Devo: Development in an Evolutionary Context

1. Evo-Devo: Development in an Evolutionary Context Dll expression En/Inv expression Control of eyespot development on a developing butterfly wing

2. Gene regulation and evolution Activation of transcription factors Signal transduction: an extracellular signal is changed to an intracellular functional change

3. Upper beak bud One gene that affects beak size and shape Probe used to identify mRNA from bone morphogenic protein-4 gene Regulated expression

4. Things to consider • Many genes (and proteins) are homologous across evolutionarily diverse groups. • Therefore, many evolutionary changes are based on • controlling the expression of homologous genes • Temporal control • Expression at different times • Expression ffor different lengths of time • Spatial control • Expression in different places (tissues). • Examples: plants in Solanaceae; Darwin finch beak development

5. Homeotic Genes and Animal Body Plans • Bilaterally symmetrical animals develop in four dimensions. • 3 spatial + temporal • Each cell has to have • 1. location information: where it is relative to other cells • 2. time: what is presently taking place in the developmental sequence. • Homeotic genes (Hox genes): (1) transcription factors determine which (2) structural genes are activated to produce (3) particular structures.

6. Location information from what gene products are present Cells or tissues located along the major body axes use positional information during development (After Strickberger.)

7. Hox genes in Drosophila (body segmentation) Occur in clusters (gene duplication) Provides positional information Colinearity: 1. Time of expression 2. A-P axis 3. Quantity of transcription factors Where genes are expressed Morphogens = signal polypeptides Hox Gene Cluster

8. Each Hox gene contains a highly conserved 180 bp sequence – the homeobox. Codes for a DNA binding segment (aa sequence) in the transcription factor. Activation of structural genes produce structures appropriate for that location. Mutations in Hox genes result in inappropriate structures for that location.

9. Mutations in Hox genes bx, pbx, and abx Mutation of Hox gene antp 1 pair of wings normally develop on body segment T2 Hox mutations change identity of T3 cells to T2 cells. Appendages appropriate for a T2 Location are produced. Ancestors of dipteran flies had 4 wings. Location information changes Rather than head segment location Cells respond as if they are in a thoracic segment

10. Diversification of animals (e.g. Cambrian “explosion” and beyond  Hox gene diversification • Hoxhomologues: in everything from sponges to humans to fungi and plants (MADS-box genes). • Therefore, Homeoboxgenes predate the origin of animals. • Example of diversification: Arthropoda • Over 1 million sp. described; millions more waiting for recognition and description • Exoskeleton; segmented body (H–T–A) and segmented legs • Paired appendages on body segments; open circulatory system

11. Crustaceans Myriapods Hexapods Chilicerates An onychophoran (velvet worm) Closest living relative of arthropods 1 pr. unjointed legs on each of the similar body segments