Subterranean Fishes of the World

3215

2013

AIM 2013

Across animal evolution the visual system plays an essential role in the ability to find food perceive the surrounding environment and escape predation. However, when an organism colonizes an environment of total darkness, vision is no longer necessary for survival. As a consequence of millions of years of evolution in the subterranean habitat, troglobitic animals such as Astyanax mexicanus have “lost” their eyes and associated visual system structures. The identity of the genes and genetic mechanisms governing eye loss in cave-dwelling morphs remain unclear, though several genes have been hypothesized. To investigate the genetic changes that accompany eye loss in Astyanax, we performed a large-scale analysis of gene expression level changes across critical developmental stages (10 hpf, 24 hpf, 36 hpf, 72 hpf, and juvenile). We subjected an integrated Astyanax transcriptome to gene ontology (GO) term searches to identify 802 genes in Astyanax with previously known eye-related functions. This gene set was then subjected to direct mRNA Illumina sequencing technology (RNA-seq) to characterize expression level alterations with robust fold-change differences between surface and cave-dwelling forms. Preliminary analyses indicated the most dramatic variation began roughly 24 hours post-fertilization, when the eye normally begins to degenerate in Pachón cavefish morphs. Additionally, several genes including crybb2, crygm3, prph2, and arr3a exhibited differences of 4-fold or greater in cave v. surface fish. These genes will be optimal candidates for forthcoming functional analysis and validation. Utilizing this powerful approach will lend additional insight to the complex mechanisms underlying to the regressive evolution of the eye in Astyanax mexicanus.

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