Meeting Abstract
The Sp family of zinc finger transcription factors is key to leg fate specification and leg outgrowth in both vertebrates and invertebrates. In the fruit fly Drosophila melanogaster, an Sp6-9 homolog activates Distal-less and thus establishes ventral appendage fate, but the incidence and functions of Sp homologs in the subphyla Myriapoda and Chelicerata are unknown. We utilized available genomes and transcriptomes of myriapod and chelicerate exemplars and conducted a bioinformatic survey of Sp gene family members across Arthropoda. We included newly sequenced developmental transcriptomes for Phalangium opilio (harvestman), Archegozetes longisetosus (mite), and Lithobius atkinsoni (centipede) to identify orthologs of Sp genes at the base of the arthropod tree of life using phylogenetic analysis. To test the function of an Sp6-9 ortholog in Chelicerata, we conducted parental RNA interference in the spider Parasteatoda tepidariorum. Here we show that the distribution of three Sp gene family members is typical across arthropods, with some losses of Sp5 in unrelated lineages. We further show that knockdown of the spider Sp6-9 ortholog results in truncation of all prosomal appendages and the loss of one body segment, consistent with a model of positive regulation of Dll by Sp6-9 in this chelicerate species. Intriguingly, spinnerets, whose evolutionary origins are not clear, do not express Sp6-9 during outgrowth, and their morphogenesis was not affected in the knockdown phenotypes. These data provide support of a conserved genetic mechanism for leg development across all arthropods, and separately suggest that specification of spinneret identity involves different mechanisms in comparison to walking legs.
