Expression of the zinc finger transcription factor Sp6–9 in the velvet worm Euperipatoides kanangrensis suggests a conserved role in appendage development in Panarthropoda

The Sp-family genes encode important transcription factors in animal development. Here we investigate the embryonic expression patterns of the complete set of Sp-genes in the velvet worm Euperipatoides kanangrensis (Onychophora), with a special focus on the Sp6–9 ortholog. In arthropods, Sp6–9, the ortholog of the Drosophila melanogaster D-Sp1 gene plays a conserved role in appendage development. Our data show that the expression of Sp6–9 during the development of the velvet worm is conserved, suggesting that the key function of the Sp6–9 gene dates back to at least the last common ancestor of arthropods and onychophorans and thus likely the last common ancestor of Panarthropoda.