1 1.1.07
Seminar Abstract:
Segmentation genes There are three hypotheses for the evolution of segmentation during bilaterian evolution. The first claims there was one segmented bilaterian common ancestor, the others claim segmentation could have arisen twice or three times independently.
The Drosophila anterior-posterior pattern is established by maternal effect genes that form gradients of proteins (like Bicoid), that activate the gap genes, then the pair rule genes (like runt, Ftz and hairy). Then the segment polarity genes (like slp1), and then the homeotic genes, to create an embryo with 14 segments.
The function of some of the Drosophila segmentation genes (like Ftz and hairy) seems to be conserved among arthropods, including spiders.
The Notch pathway has a key role in vertebrate segmentation (somitogenesis) but is not involved in Drosophila body segmentation. The vertebrate segmentation clock controls the periodic expression of ‘cyclic genes’ (like Notch, delta and Lfn), which are all related to this pathway.
The Notch and Delta proteins are involved in segmentation of an arthropod, the spider Cupiennius salei, a fact that contributes to the hypotheses that sees segmentation having arisen independently three times in the lineages leading to vertebrates, annelids and arthropods.
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