Double-stranded RNA interference in the spider Cupiennius salei: the role of Distal-less is evolutionarily conserved in arthropod appendage formation

Chelicerates represent a basal arthropod group, which makes them an excelle nt system for the study of evolutionary processes in arthropods. To enable functional studies in chelicerates, we developed a double-stranded RNA-inte rference (RNAi) protocol for spiders while studying the function of the Dis tal-less gene. We isolated the Distal-less gene from the spider Cupiennius salei. Cs-Dll gene expression is first seen in cells of the prosomal segmen ts before the outgrowth of the appendages. After the appendages have formed , Cs-Dll is expressed in the distal portion of the prosomal appendages, and in addition, in the labrum, in two pairs of opisthosmal (abdominal) limb b uds, in the head region, and at the posterior-most end of the spider embryo . In embryos, in which Dll was silenced by RNAi, the distal part of the pro somal appendages was missing and the labrum was completely absent. Thus, Dl l also plays a crucial role in labrum formation. However, the complete lack of labrum in RNAi embryos may point to a different nature of the labrum fr om the segmental appendages. Our data show that the expression of Dll in th e appendages is conserved among arthropods, and furthermore that the role o f Dll is evolutionarily conserved in the formation of segmental appendages in arthropods.