paused RNA polymerase II; gene promoter; Heat-shock protein 90; phenotypic variation; genotype-phenotype relation; Drosophila
Friedensohn Simon, Sawarkar Ritwick (2014), Cis-regulatory variation: significance in biomedicine and evolution., in Cell and tissue research
, 356(3), 495-505.
Heat-shock protein 90 (Hsp90) is a chaperone required to keep key signaling molecules and transcription factors in a poised state before activation by stimuli. Our recent findings have shown that the chaperone also targets to several promoters in the genome keeping RNA polymerase II in a paused state before gene induction. Besides these broad molecular roles, Hsp90 is thought to minimize genetic variation in animals and plants to reduce phenotypic variation of the population. This ability of the chaperone has led to the belief that Hsp90 occupies a central position in genotype-phenotype relation and in potentiating evolution. However, there is little evidence how molecular actions of Hsp90 in a cell relate to its organismal and evolutionary functions. This important gap in understanding has motivated the current proposal. The study will make use of Drosophila genetics reference panel (DGRP) composed of 192 individual genetically homogenous strains arising from one outbred natural population. The genomes of all the lines have been fully sequenced. In a preliminary analysis of the publicly available genome sequences, we discovered a significantly large natural variation at promoters that are targeted by Hsp90 compared to other promoters, making this an ideal system in which to study genotype-phenotype relation in the context of promoter-bound Hsp90. The proposed study will first identify the type of naturally occurring genetic variation that can be acted upon by Hsp90 - i.e. if coding region or regulatory variation is minimized by the chaperone. Next, the proposal will directly test the hypothesis that phenotypic variation released by Hsp90 can potentiate artificial selection regime. The selection will be closely monitored by sequencing Drosophila genomes to identify genetic variation. An advantage of the study is that the controlled genetic conditions allow for a molecular investigation, which will be performed by quantifying gene-expression variation in developing embryos of known genotypes when Hsp90 activity is compromised. Furthermore, the direct effect of polymorphism in regulatory regions will be tested by transgenic reporter lines in cells and flies. Finally, a computational framework will link the phenotypic variation of known genotypes with binding sites of Hsp90 and transcription factors to integrate molecular genetic signatures in phenotypic variation. This I would like to argue will be a synthesis of modern molecular biology with traditional tenets of evolution. The molecular understanding of genotype-phenotype link obtained in the proposed study will certainly benefit the ongoing genome-wide association studies in humans. This has a strong bearing in personalized medicine and fundamental assumptions thereof. Moreover, Hsp90 inhibitors are in clinical trials for cancer therapy, and any knowledge about unintended effects these may have on phenotype will be extremely relevant in designing future therapeutic strategies. In summary, a detailed understanding of Hsp90’s role in connecting genotype with phenotype using controlled Drosophila experiments will contribute to several areas of biological research.