Hox, ParaHox and NK: the germ layers, the tail and early animal evolution

Question 1

ways of determining origins of bilaterian body plans

Answer 1

looking at genes- 1699 ‘new’ genes in bilateria, but none of them retained by all species- the evolutionary distance is too big

looking at hypithesis- e.g. that a particular gene class is important

Question 2

what do hox genes seem to pattern?

Answer 2

different tissue layers in different species- e.g. ectoderm in most species- also some mesoderm in drosophila, some endoderm in c elegans

hox genes patterning the nerve cord in early bilateria?

Question 3

NK class gene

Answer 3

Hox-like gene cluster- in drosophila, also seems to be present but split up in drosophila

Question 4

where are NK class genes expressed?

Answer 4

mesoderm, mostly

Question 5

example of NK class genes

Answer 5

tinman- involved in heart dev
slouch- involved in muscle development

Question 6

NK class gene general function

Answer 6

patterning bits of the body, rather than along an axis

Question 7

ParaHox gene cluster- where was it discovered, how is it distributed etc

Answer 7

3 gene cluster

discovered in amphioxus, lost one of the genes in species like drosophila

Question 8

what do ParaHox genes do?

Answer 8

seem to pattern the endoderm- e.g. Pdx expression in the endoderm in mice, relation to diabetes in humans

Cdx expression in the gut/anus in drosophila, frogs, etc (knockouts literally have no bum and explode)

Question 9

weird things about ParaHox cluster

Answer 9

Gsx is not expressed where we would expect it- expressed in the brain rather than the mouth like we would think

-but it is expressed in the mouth of molluscs- also the brain still though

Question 10

age of these gene clusters

Answer 10

slightly older than bilateria which is awks- all 3 in cnidaria, NK cluster also in sponges

-possible recruitment at the bilateria?

Question 11

a potential other set of genes which may have been important in the transition to bilateria

Answer 11

Fox class TFs- also involved in mesoderm patterning and seem to have been recruited early in animal evolution

Question 12

example of genes from diff locations being brought together

Answer 12

NK genes (not the other NKs) came together in deuterostomes, and stayed together- expression in the pharynx