Subterranean Fishes of the World

3899

2016

Depigmentation is one of the most common features evolving in cave animals. The melanin synthesis pathway has been well studied in vertebrates, providing a rich source of candidate molecules for analysis. For instance, melanin synthesis involves the transport of L-tyrosine substrate into the melanosome, the conversion of L-tyrosine to L-DOPA and L-DOPA to L-DOPAquinone by the rate-limiting enzyme tyrosinase (Tyr). This process leads to the production of black eumelanin pigment from L-DOPAquinone via a sequence of downstream reactions promoted by the melanogenic enzymes tyrosinase, tyrosinase-related protein 1 (Tyrp1), dopachrome tautomerase (Dct or Tyrp2), and others. To understand the molecular mechanisms underlying the evolution of depigmentation in Astyanax cavefish, we specifically evaluated expression of the tyrosinase gene family including Tyr, Tyrp1a, Tyrp1b, as well as the genes Dct and Pmela gene. We first evaluated expression level differences in mRNA level using RNA-seq analysis, and then performed whole-mount in situ hybridization on early stage embryos of surface fish and Pachón cavefish. Our results indicate that all genes are down-regulated in Pachón cavefish embryos which have fewer cells expressing these genes compared to surface fish. In situ analyses revealed distribution of pigmentation cells principally on the head and flank areas. Knockdown of these genes using morpholinos in zebrafish embryos resulted in variable melanosome defects. The differential expression levels we observed for Dct, Tyr, Tyrp1a, Tyrp1b and Pmela reveal that melanosomes are generated and activated during melanin synthesis, but do so at very different rates and levels between surface and cave forms. Altogether, our results suggest that multiple steps and genes in the melanin synthesis pathway have been targeted during the evolution of depigmentation in cavefish.

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23rd International Conference on Subterranean Biology

2016

2016

2016