Meeting Abstract
The deutocerebral (second) segment of the head is putatively homologous across Arthropoda. In Mandibulata, this segment bears a pair of antennae, and in Chelicerata, a pair of chelicerae. Our recent work revealed a common mechanism for differentiation of deutocerebral appendages across arthropods, via experimental data for homothorax, a determinant of deutocerebral appendage fate, in an arachnid exemplar. In spite of this discovery, the architecture of the archetypal insect antenna and arachnid chelicera is markedly different, suggesting the downstream interactions of homothorax may not be similarly conserved. To test this hypothesis, we explored gene expression and/or function of members of the appendage fate specification gene regulatory network (GRN) in multiple chelicerate and mandibulate species. Here we show that strong expression of spineless (a known distal antennal selector in holometabolous insects) in the distal territory of the developing insect antenna is similarly observed in the distal antennae of other mandibulate exemplars. Functional data from the hemimetabolous insect Oncopeltus fasciatus, which bears a simple, plesiomorphic antenna, demonstrate that RNAinterference-mediated knockdown of spineless incurs homeotic distal antenna-to-leg transformations, comparable to data from holometabolous insect counterparts. By contrast, we show that spineless orthologs are not expressed at all in the cheliceral limb buds of spiders or harvestmen during developmental stages where appendage identity is conferred. These data demonstrate a strong correlation between the expression pattern of spineless and the distal architecture of the deutocerebral appendage. Together with ongoing experiments, this work aims to reconstruct the evolution of the appendage fate specification GRN across Arthropoda.
