Subterranean Fishes of the World

5691

2015

AIM 2015

Depigmentation is one of the most common phenotypes evolving in Astyanax cavefish. The identification and characterization of genes controlling coloration will enable us to better understand the genetic and evolutionary mechanisms underlying cavefish depigmentation. To understand the genetic differences of pigment cell development between surface fish and cavefish, we identified 165 pigment-related transcripts from prior QTL studies and the literature. We analyzed 158 genes from the current draft of the Astyanax genome, distributed across 133 scaffolds, and found 95 genes harbored SNP changes, and 75 genes harbored other coding sequence changes. We quantified mRNA expression level differences in these 75 genes in surface fish and cavefish across early development and identified 50 genes with expression level fold-change differences between surface and Pachón cavefish >1.5. We further examined whether the expression levels change appeared in two geographically-distinct populations from the Sierra de El Abra – Pachón and Tinaja. Our results identified 17 genes that are down-regulated in both cave populations and 7 genes which are up-regulated in both cave populations. When we performed sequence alignments of the 75 genes, we observed similar coding sequence changes in both Pachón and Tinaja cave populations. In addition to the 75 genes with coding region changes, we discovered several genes with intact coding sequences that have significant mRNA expression level changes. Based on the literature, many of these identified genes play a role in neural crest migration, melanophore lineage determination, and melanoblast survival, migration and proliferation. Thus, the candidate genes identified from this analysis are involved in many diverse aspects of pigmentation development. Further, the presence of both coding and expression-level differences implies that diverse genetic processes collectively underlie the convergent loss of pigmentation in Astyanax cavefish. Future studies will include developmental analyses of gene expression based on in situ hybridization and pigmentation phenotypic assays. By better understanding the temporal and spatial aspects of pigment gene expression across differentiation, migration, and proliferation stages, we hope to better understand the molecular mechanisms underlying the evolution of depigmentation in Astyanax cavefish.

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