Meeting Abstract
Troglobites exhibit extreme phenotypic changes such as eye loss, albinism, and expanded non-visual senses. The Mexican tetra, Astyanax mexicanus, includes a cave-dwelling morph which harbors a number of regressive phenotypes that can be compared to closely-related surface-dwelling morphs. Despite clear phenotypic differences between these morphs, less is known of the genetic underpinnings of these traits. To identify putative genetic differences, we screened the Astyanax genome for indel mutations using RNA-sequencing reads derived from three independent populations. We confirmed the presence of seven indel mutations in genes associated with blood physiology, growth factor signaling, and collagen structure. Six mutations differed in the surface-dwelling population, with one varying in the Tinaja cave population. Here, we present in situ hybridization (ISH) analyses at three embryonic stages, designed to visualize expression differences of these genes between populations. Two genes, mki67 and ghrb, were expressed at substantially higher levels in cavefish, while expression of plg appeared to mark the developing liver, which grows at a much faster rate in cavefish compared to surface morphs. Three genes showed rather diffuse staining with similar expression patterns in all three populations. The gene mlf1, associated with blood progenitor specification, was expressed at similar levels in cave and surface fish, however the mutation is predicted to be deleterious in cave morphs. Overall, this work demonstrates the value of deep-sequencing as a means of identifying genomic mutations in an evolutionary system. The integration of whole-mount expression analysis deepens our understanding of how indel mutations may impact, or arise as a consequence of, life in total darkness.
