15-P021 Drosophila anterior determination is independent of Bicoid morphogenic functions but depends on activating versus repressing inputs on the level of target gene enhancers

Our analyses of early neurogenesis in several representatives of chelicerates (e.g. spiders) and myriapods (e.g. millipedes) have revealed that the genetic network involved in recruitment and specification of neural precursors is conserved in all euarthropod groups. However, the expression pattern and function of these genes is adapted to the distinct morphology of neural precursor formation in each group. We observed several molecular and morphological characters in the developing central and peripheral nervous system of chelicerates and myriapods that cannot be found in equivalent form in insects and crustaceans. It is possible that these characters are shared derived characters (synapomorphies) of myriapods and chelicerates, providing the first morphological support for a clade uniting these two groups. However, they could also represent ancestral characters (symplesiomorphies) retained in myriapods and chelicerates and lost in the more derived insects and crustaceans. We have therefore analysed neurogenesis in a representative of an outgroup to the euarthropods, the onychophoran Euperipatoides kanangrensis. We have identified Notch and Delta homologues in Euperipatoides kanangrensis. These genes are involved in specification of neural stem cells in insects. We show that they are expressed in a distinct pattern which is neither comparable to insects/crustaceans nor to chelicerates/myriapods. Furthermore, we have analysed the morphology of neural precursor formation by F-actin staining and light microscopic sections. The data suggest that at least some of the characters shared by chelicerates and myriapods are synapomorphies