Meeting Abstract
33.1 Friday, Jan. 4 Distal-less and dachshund pattern both plesiomorphic and apomorphic structures in chelicerates: RNAinterference in the harvestman Phalangium opilio (Opiliones) SHARMA, P/P*; SCHWAGER, E/E; GIRIBET, G; JOCKUSCH, E/L; EXTAVOUR, C/G; Harvard University; Harvard University; Harvard University; University of Connecticut; Harvard University psharma@post.harvard.edu
The discovery of genetic mechanisms whereby a morphological structure is transformed from a plesiomorphic (=primitive) state to an apomorphic (=derived) one is a cardinal objective of evolutionary developmental biology. However, this objective is often encumbered for many lineages of interest by limitations in taxonomic sampling or in genomic resources for the few available laboratory model organisms. In order to investigate the evolution of appendages within Chelicerata, the putative sister group of the remaining arthropods, we sequenced a developmental transcriptome of the harvestman Phalangium opilio. Concomitantly, we developed an RNAinterference protocol for this species. We silenced the leg gap genes Distal-less (Dll) and dachshund (dac) in the harvestman via zygotic injections of double-stranded RNA. Consistent with the conserved roles of these genes in patterning the proximo-distal axis, we observe that embryos injected with Dll dsRNA lack distal parts of appendages or appendage-like structures, such as the labrum, the chelicerae, the pedipalps, and the walking legs; whereas embryos injected with dac dsRNA lack the medial podomeres femur and patella in the pedipalps and walking legs. In addition, we observe the involvement of these genes in patterning structures that do not occur in well-established chelicerate models (spiders and mites). Embryos injected with Dll dsRNA additionally do not develop the preoral chamber formed from pedipalpal and leg coxapophyses, or the ocularium, a dorsal outgrowth that bears the eyes. A single embryo injected with dac dsRNA was observed to lack the proximal segment of the chelicera, a plesiomorphic podomere wherein dac is expressed in wildtype embryos.
