ASW has first been characterized in a genetic screen searching for genes differentially expressed in early neural specification in Xenopus laevis [127] . Although this study could demonstrate that alteration of ASW levels in X. laevis leads to severe developmental defects, it provided limited insights into mechanistic aspects of ASW function. ASW has been speculated to be specific for vertebrates as no homologous genes were detectable in Drosophila melanogaster or Caenorhabditis elegans [127] . Nonetheless, homologues of ASW are detectable in the genomes of at least some arthropods and nematodes (Fig. 5A) . Future studies might answer the question of whether the link between ASW and HSPC117 explains any of the developmental defects observed upon manipulation of ASW levels in X. laevis.