Prospero and Snail expression during spider neurogenesis

Analysis of early neurogenesis in the spider Cupiennius salei (Chelicerata, Aranea, Ctenidae) has shown that the cells of the central nervous system are recruited from clusters of cells that invaginate from the neuroectoderm. This is in contrast to Drosophila, where only single cells delaminate and become neuroblasts, the stem cells of the nervous system. In order to compare the processes further, we have cloned homologues of the pan-neural Drosophila genes prospero and snail from the spider and have analysed their RNA and protein expression pattern. We find that snail expression is transient and only a subset of neural cells expresses Snail protein at any given time, making it difficult to assess whether it is indeed a pan-neural gene in the spider. Prospero protein expression, on the other hand, is seen in all invaginating cells and continues throughout differentiation of the neurons. In contrast to Drosophila, asymmetric localization cannot be detected, even in cells that still divide. Our results provide no evidence for neuroblasts or stem cells in the spider, although there are a limited number of mitoses in the cells that are derived from the invaginating clusters. These aspects of spider neurogenesis are more similar to the neurogenesis process known from vertebrates.