Distal‐less and dachshund pattern both plesiomorphic and apomorphic structures in chelicerates: RNA interference in the harvestman Phalangium opilio (Opiliones). Issue 4 (14th May 2013)

• Record Type: Journal Article
• Authors: Sharma, Prashant P.; Schwager, Evelyn E.; Giribet, Gonzalo; Jockusch, Elizabeth L.; Extavour, Cassandra G.
• Is Part Of: Evolution & development. Volume 15:Issue 4(2013)
• Page Start: 228
• Page End: 242
• Publication Date: 2013-05-14
• Subjects: Evolution (Biology) -- Periodicals; Developmental biology -- Periodicals; 576.82
• DOI: 10.1111/ede.12029
• Languages: English
• ISSNs: 1520-541X

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>SUMMARY</title> <sec id="ede12029-sec-0001" sec-type="section"> <p>The discovery of genetic mechanisms that can transform a morphological structure from a plesiomorphic (=primitive) state to an apomorphic (=derived) one is a cardinal objective of evolutionary developmental biology. However, this objective is often impeded for many lineages of interest by limitations in taxonomic sampling, genomic resources, or functional genetic methods. In order to investigate the evolution of appendage morphology within Chelicerata, the putative sister group of the remaining arthropods, we developed an RNA interference (RNAi) protocol for the harvestman <italic>Phalangium opilio</italic>. We silenced the leg gap genes <italic>Distal‐less</italic> (<italic>Dll</italic>) and <italic>dachshund</italic> (<italic>dac</italic>) in the harvestman via zygotic injections of double‐stranded RNA (dsRNA), and used in situ hybridization to confirm RNAi efficacy. Consistent with the conserved roles of these genes in patterning the proximo‐distal axis of arthropod appendages, we observed that embryos injected with <italic>Dll</italic> dsRNA lacked distal parts of appendages and appendage‐like structures, such as the labrum, the chelicerae, the pedipalps, and the walking legs, whereas embryos injected with <italic>dac</italic> dsRNA lacked the medial podomeres femur and patella in the pedipalps and walking legs. In addition, we detected a role for these genes in patterning structures that do not occur in well‐established chelicerate models (spiders and mites). <italic>Dll</italic> RNAi additionally results in loss of the preoral chamber, which is formed from pedipalpal and leg coxapophyses, and the ocularium, a dorsal outgrowth bearing the eyes. In one case, we observed that an embryo injected with <italic>dac</italic> dsRNA lacked the proximal segment of the chelicera, a plesiomorphic podomere that expresses <italic>dac</italic> in wild‐type embryos. This may support the hypothesis that loss of the cheliceral <italic>dac</italic> domain underlies the transition to the two‐segmented chelicera of derived arachnids.</p> </sec> </abstract>