On the gene network of blind Arachnids

Come check some blind arachnids! A Retinal Determination Gene Network homolog is necessary for patterning the eyes of whip spiders:


A Eye arrangement in Amblypygi

B Charinus ioanniticus (Kritscher, 1959)

C Charinus israelensis Miranda, Aharon, Gavish-Regev, Giupponi & Wizen, 2016

Only little is known on how eyes of arachnids are formed genetically, and nothing is known on the mechanisms of eye reduction and loss in troglomorphic arachnids. In this manuscript, we investigated two sister species of whip spiders found in caves in Israel (Arachnopulmonata, Amblypygi, Charinus) of which one species has reduced eyes. We generated the first embryonic transcriptomes for Amblypygi at Sharma Lab, and found that there are some RDGN homolog duplications, and that the paralogy of RDGN homologs is systemic across
arachnopulmonates (arachnid orders that have booklungs) and not specific to spiders.

We collected, in jointed field excursions in Israeli caves gravid females of Charinus israelensis and Charinus ioanniticus , and used their embryos in a differential gene expression (DGE) analysis (Israel Team: Efrat Gavish-Regev, Shlomi Aharon and Igor Armiach Steinpress; US team: Prashant Sharma, Guilherme Gainett, and Jesus Ballesteros; Israel National Parks Authority permit 2018/42037; National Geographic Society Expeditions Council grant no. NGS-271R-18). We compared the expression of RDGN genes from both species, and identified candidate RDGN genes involved in the formation and reduction of eyes in whip spiders. We found expression patterns of three candidate RDGN genes in DGE experiments, using RNAi in the spider Parasteatoda tepidariorum. In this manuscript we provide functional evidence that one of these paralogs is necessary for the development of all arachnid eye types. Our results support the conservation of at least one RDGN component across Arthropoda and establish a framework for investigating the role of gene duplications in arachnid eye diversity.

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