Unraveling the role of molecular capacitors that obscure cryptic genetic variation in Astyanax mexicanus during the evolution of eye loss

PROJECT SUMMARY / ABSTRACT Personalized medicine and genetic counseling frequently run up against the problem of hidden variability. Low- penetrant phenotypes complicate predictions about the severity of genetic diseases, even within a single family. Disconnect between genotype and phenotype has profound consequences for individuals and

populations. ‘Cryptic’ alleles can accumulate in a population, shifting the genetic landscape and, when revealed, altering disease prevalence and evolutionary trajectory. Molecular systems can buffer the effects of such variation, however, when these are de-stabilized, previously cryptic variants are exposed, producing

novel phenotypes. Hsp90, an essential chaperone that stabilizes kinases, chromatin remodelers, and signal transducers, may act as a ‘capacitor,’ buffering genetic variation until it is released upon environmental insult. Inhibition of Hsp90 reveals cryptic variants in yeast, plants, worms, flies, and fish. In Astyanax mexicanus, a

teleost species that evolved eyeless cave populations, Hsp90 inhibition expands variation in eye size, suggesting that Hsp90 perturbation may have played a role in the evolution of eye loss in these fish. While there is substantial support for Hsp90’s role in buffering genetic variation, the mechanism(s) by which buffering

occurs, its role in development, and its impact on morphological change across generations remains to be elucidated. Understanding the limits of Hsp90 buffering has profound implications for research into the genetic determinants of development and disease within individuals and across populations. My work aims to use eye

loss in cavefish as a natural model of Hsp90 capacitance, specifically testing the central hypothesis that the chaperone acts on key factors in eye development pathways to suppress variation. By intersecting Astyanax genomics, Hsp90-client interactions, and genetic tools in zebrafish, this proposal will identify the

genes that contribute to Astyanax eye loss, examine the role of Hsp90 in development, and determine the capacity of Hsp90 to contribute to evolutionary leaps. During the K99 phase, I will use gene knock-outs in zebrafish to identify Hsp90-dependent genes that contribute to eye loss in Astyanax, uncovering novel roles for

Hsp90 clients in eye development. During the R00 phase, I will investigate the role of Hsp90 in development, abrogating its activity in the developing zebrafish to identify tissues and pathways that are sensitive to Hsp90- buffering. I will also assess the contribution of Hsp90 to eye evolution in the lab. Completion of these aims will

expand our understanding of genetic determinants of eye development, identify Hsp90-sensitive tissues and pathways that may be susceptible to low-penetrance disorders or evolutionary leaps, and more broadly determine the contribution of Hsp90 to observed ‘hidden variability.’ During the K99 phase, under Drs. Cliff

Tabin and Matthew Harris, I will obtain essential training in Genetics and Development and receive guidance on best practices for rigorous experimental design. The proposed research and training will provide a foundation for the success of my independent academic laboratory.