Neurogenesis in the spider: new insights from comparative analysis of morphological processes and gene expression...

While there is a detailed understanding of neurogenesis in insects and partially also in crustaceans, little is known about neurogenesis in chelicerates. In the spider Cupiennius salei Keyserling, 1877 (Chelicerata, Arachnida, Araneae) invaginating cell groups arise sequentially and in a stereotyped pattern comparable to the formation of neuroblasts in Drosophila melanogaster Meigen, 1830 (Insecta, Diptera, Cyclorrhapha, Drosophilidae). In addition, functional analysis revealed that in the spider homologues of the D. melanogaster proneural and neurogenic genes control the recruitment and singling out of neural precursors like in D. melanogaster. Although groups of cells, rather than individual cells, are singled out from the spider neuroectoderm which can thus not be homologized with the insect neuroblasts, similar genes seem to confer neural identity to the neural precursor cells of the spider. We show here that the pan-neural genes snail and the neural identity gene Krüppel are expressed in neural precursors in a heterogenous spatio-temporal pattern that is comparable to the pattern in D. melanogaster. Our data suggest that the early genetic network involved in recruitment and specification of neural precursors is conserved among insects and chelicerates.