BIOL Topic 13

Anterior

-near head

posterior

-near abdomen

gene expression over time

fertilization, embryogenesis, adult

toolkit genes

-the set of genes responsible for the regulation of animal development

-there are only ~few dozen to 100s of tool kit genes

-mostly encode cell signalling proteins and transcription factors

-highly conserved across diverse species of animals

classes of toolkit genes involved in regulating the anteroposterior body axis

earlier-maternal effect genes, gap genes, pair-rule genes, segment-polarity genes, hox genes-later

maternal-effect genes establish the A-P axis

-bicoid and nanos mRNA are tetherd to the anterior and posterior ends of the unfertilized egg

-upon fertilization, the proteins are expressed and form a gradient

-bicoid and nanos encode transcription factors that regulate expression of the next set of genes

-maternally expressed

-function: determine the major body axis

maternal-effect genes

mutant phenotypes of maternal-effect genes depend only on the genotype of the egg parent

segmentation genes

-gap genes, pair rule genes, segment polarity genes (in that order)

--zygotically expressed

gap genes

-divide embryo into broad regions and turn on next gene

-Mutations in gap genes lead to large gaps in segmentation

-zygotically expressed

-function: define broad sections

pair-rule genes

-affect the development of pairs of segments and turn on next gene

-act in more narrow regions that do gap genes

-alternating (turn on the next)

-zygotically expressed

-function: define individual segments

segment polarity genes

-affect the organization of segments

-mutations in segment polarity genes lead to defects in segment polarity

-zygotically expressed

-function: organization within a segment

hox genes

-determine the identity of a structure or segment

-encodes transcription factors

-zygotically expressed

hox proteins

-turn on similar genetic programs in different species

-these genes play a fundamental role in the development of most animals

How do Hox genes control the identify of segments and appendages?

-they regulate the expression of networks of other genes

-hox genes encode sequence specific DNA-binding proteins (transcription factors)

-they bind to cis-acting regulatory elements (enhancers and/or promoters) of other genes to activate or repress them