L35 Evolution and Development

Question 1

Linking genes to body plan

Answer 1

See onenote

What sort of genes might evolution act upon?

• effector genes
• regulatory genes

Question 2

Diversification of body plan - 3 possibilities

Answer 2

1. different gene sets in various species
2. same gene sets - difference sin regulation in various species
3. same gene sets - differences in coding region in various species

Genes = gene involved in specifying body plan

Question 3

Key question

Answer 3

Do species that differ in body plan differ in their complements of genes that specify body plan?

Conservation of genes sets, diversity of body plans

Question 4

Mutant screen for body plan genes

Answer 4

see onenote

Question 5

Over 100 genes discovered

Answer 5

• controlled embryonic development in Drosophila
• most shown to have similar roles in humans
• evidence for both similar gene sets and functions

Question 6

Mutations fell into categories

Answer 6

see onenote

Question 7

Homeotic transformations

Answer 7

Antennapedia mutant = legs form instead of antenna

Antennapedia is a HOM-C gene first discovered in Drosophila which controls the formation of legs during development. Loss-of-function mutations in the regulatory region of this gene result in the development of the second leg pair into ectopic antennae.

Question 8

Ubx

Answer 8

• ultrabithorax

Ubx mutant = Ubx no longer expressed, gets wing instead of haltere

Ubx stops formation of wings

If you gain more Ubx expression = loss of wings

In Drosophila melanogaster it is expressed in the third thoracic (T3) and first abdominal (A1) segments and represses wing formation.

Question 9

Hox genes

Answer 9

regulate the identity of serially repeated structures in vertebrates

regulate the identity of body parts

Order of the genes on the chromsoome is the same as the order it is expressed on the body axis - colinearity

internal organs also controlled by hox genes

ancient

Question 10

Homeotic genes

Answer 10

• encode TF (regulatory genes)
• control expression of very large numbers of downstream genes that establish what a given body segment/tissue will become

Homeotic genes contain a sequence of DNA known as a homeobox, which encodes a segment of 60 amino acids within the homeotic transcription factor protein.

Question 11

Abd-B

Answer 11

see onenote

• required for formation of posterior spiracle

Question 12

Abd-B downstream regulatory pathway

Answer 12

see onenote

Abd-B have four direct targets which are also regulatory genes

• The genes that the regulatory genes control, controls body plan
• Through downstream regulation

Expression of Abd-B activates gene regulatory program

Question 13

Homeobox genes

Answer 13

The DNA-binding piece of a Hox protein is called the homeodomain, and it’s encoded by the homeobox.

All TF
All have DNA binding domain
Homeo domain is incredibly conserved

Question 14

Same gene sets - differences in regulation in various species

Answer 14

see onenote slides

• in situ hybridisation
• shifting patterns of hox gene expression across arthropods

changes in body plan consistent with changes in pattern of gene expression and known function of genes BUT it is only a correlation

Question 15

Disrupting gene expression

Answer 15

see onenote

Can manipulate non-model organisms with RNAi
- Knocking down the gene product (not the gene), not super effective

Antp RNAi
Ubx RNAi

disruption of hox gene expression changes body plan BUT no proof that this is the explanation for diversity of body plans

Question 16

Ubx RNAi

Answer 16

Ubx strongly expressed in segment A1 => partial transformation of segment A1 to thoracic segment (with leg)