Defining more rules of environmental and phenotypic buffering

Abstract

Phenotypes and organisms are robust, or ‘buffered,’ and thus able to withstand environmental and mutagenic disturbances to maintain wild-type functions. However, the specific mechanisms that ensure phenotypic buffering, and the degree to which these mechanisms overlap, remain poorly understood. The first mechanism I focused on was buffering of phenotype from both de novo and pre-existing genetic variation. The best characterized agent of buffering pre-existing ‘cryptic’ genetic variation is the molecular chaperone HEAT SHOCK PROTEIN 90 (HSP90). I found that when HSP90 was inhibited, the penetrance and heritability of de novo genetic variation increased. For pre-existing genetic variation, I characterized a novel phenotypic buffering factor, ARGONAUTE 1 (AGO1), a key player in microRNA-mediated gene regulation. When AGO1 was genetically perturbed, phenotypes not only became unbuffered but also highly correlated traits became uncoupled. AGO1 is also a known client of HSP90. Despite this interaction, data in this dissertation support that AGO1’s phenotypic buffering capabilities are largely independent of HSP90. For the second mechanism, I studied AGO1’s capacity to buffer and integrate environmental stimuli. I identified in ago1 mutants a novel, stress-induced phenotype and traced it to misinterpretation of environmental cues. The third mechanism I examined was whether redundancy within a gene family contributes significantly to buffering a developmental trait. In this particular case, phenotypic buffering comes from a single gene within the family. In sum, the data I generated indicates that organisms use several, somewhat overlapping mechanisms to ensure stability of developmental traits and proper responses to the environment.