Subterranean Fishes of the World

5628

2022

AIM 2022

34

The absence of eyes and skin pigmentation are perhaps the most recognizable traits in cave-dwelling compared to river-dwelling Astyanax mexicanus. However, cave forms have also evolved novel traits that allowed them to survive in the harsh conditions experienced in cave environments. One of the most unforgiving of these environmental pressures is the scarcity of food which probably created a selective pressure to evolve specialized metabolic adaptations to endure such conditions. Some of the traits seen in cave forms are related to glucose and fat metabolism, such as extreme adipose tissue accumulation, systemic glucose dysregulation, hyperphagia and reduced inflammation response. To uncover the genetic basis behind these divergent physiologies between surface and cavefish, we took advantage of the interfertility of the cave and surface fish and conducted a quantitative trait locus (QTL) analysis for metabolic traits of Pachón- Surface F2 offspring, with the aim of discovering the loci responsible for the metabolic specializations in cavefish. We used genotype by sequencing to retrieve 6,622 postfiltered markers in 426 F2 offspring and constructed a genetic map to map a variety of metabolic traits including fasting blood glucose concentrations. We also mapped the levels of gene expression in F2 fish as additional traits, by choosing the most differentially expressed genes of visceral adipose tissue and skeletal muscle in the cave and surface forms. Fasting blood glucose show a QTL that locates in chromosome 6, in a narrow interval centered at the type 2 diabetes and obesity related gene, nuclear receptor coreceptor 2 (ncor2) . NCOR2 proteins show at least 14 amino acid substitutions between the two forms, some of them polymorphic in either or both populations, as well as other non-polymorphic and non-functionally equivalent amino acid substitutions. Our F2 gene expression analysis also revealed strong expression QTL, which locate in cis relative to the gene its expression was being quantified (cisQTL). We are currently analyzing the impact of the ncor2 gene and the possible role of cis-regulatory elements that could be associated with the cisQTL, in their role of glucose dysregulation and adipose tissue accumulation as an strategy to specialized physiological adaptations of the cavefish.

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