熱休克蛋白90調控酵母菌基因型與外表型的轉換

Hsp90 regulates genotype-to-phenotype transition among wild isolates of Saccharomyces cerevisiae

洪柏湘(Po-Hsiang Hung)

指導教授 ： 呂俊毅

共同指導教授 ： 蔡懷寬

國立臺灣大學/生命科學院/基因體與系統生物學學位學程/博士(2019年)

https://doi.org/10.6342/NTU201901350

摘要

在族群中生物個體間表現型的變異越大越有助於物種存活在劇變的環境當中，而表現型的變異大多是受到遺傳變異的影響。熱休克蛋白90 (Hsp90) 是一種真核生物的必需蛋白質，它可以抑制和促進不同遺傳變異的效應，當細胞面臨環境壓力時，生物體內的熱休克蛋白90不足以維持其原本的功能，導致它調控的遺傳變異的效應顯現或是消失，藉由這樣的調控，熱休克蛋白90可以迅速的因應環境的變異，造成表現型的變化。這樣的調控機制從酵母菌到人類都有被發現，在這篇研究中，我想探討熱休克蛋白90調控外表型的機制在野生酵母菌中是否是常見的呢？這篇研究藉由五株不同的酵母菌株探討這個問題，我透過次世代定序的技術，首先分析酵母菌株在正常環境和熱休克蛋白90受抑制時的基因表現量的差異。不同的酵母菌株對於熱休克蛋白90受抑制時的反應是不同的，其中一個可能是菌株間的遺傳變異因為熱休克蛋白90的調控而造成這樣的現象。為了更進一步的探討這個問題，我建構了一套資訊分析的流程去探討(1)遺傳變異影響轉錄因子結合序列時，是否會造成這個現象;(2) 除了影響轉錄因子結合序列，遺傳變異的效應是否會透過特定的轉錄因子造成表現量變化。我用實驗實際驗證分析的候選轉錄因子，這些轉錄因子在熱休克蛋白90受抑制時，其表現量或活性會有菌株間的差異，而這些差異也影響了外表型的變化。因為高溫環境會導致熱休克蛋白90不足以維持其原本的功能，我也測試高溫環境能不能再現由熱休克蛋白90抑制劑引起的菌株差異，結果發現不論是轉錄因子的活性或是外表型的差異都能在高溫環境中顯現。因此這篇研究發現在壓力環境下酵母菌細胞的熱休克蛋白90可以透過轉錄調控，造成菌株間的表現型變異，而這樣的調控有助於細胞展現不同外表型，進而有機會存活在壓力環境中。

關鍵字

熱休克蛋白90 ； 基因遺傳緩衝效應 ； 轉錄調控

並列摘要

Enhanced phenotypic diversity increases the chance of a population to survive in catastrophic conditions. Hsp90, an essential molecular chaperone in eukaryotes, has been suggested to suppress (a.k.a. buffer) or enhance (a.k.a. potentiate) the effects of genetic variation, enabling organisms to adjust the level of phenotypic diversity in response to environmental cues. Does the Hsp90-mediated phenotypic diversification commonly occur in the natural population and provide the chance for cells to survive in changing environments? By examining gene expression profiles of five phylogenetically distant yeast strains, we found hundreds of Hsp90-dependent strain-specific differential gene expression. Thus, the Hsp90-mediated strain-specific expression differences commonly occurred in the wild isolates. I hypothesized the differences result from the effects of Hsp90-regulated genetic variations. The genetic variations transmitted their effects to the downstream transcription factors and then led to the strain-specific Hsp90-dependent regulation of transcription factors. An analysis pipeline was developed to identify the potential transcription factors leading to the expression variation. More than 85% of the genes showing Hsp90-dependent expression variations are regulated by trans factors. I experimentally verified the trans effects by showing the transcriptional activity of trans factors have different Hsp90-dependency among strains and cause the strain-specific expression differences on their targets upon Hsp90 is inhibited. The widespread expression changes on the trans targets perfectly predicted the phenotypic variations among strains under the stress conditions combined with the Hsp90 inhibition. More importantly, not only the Hsp90 inhibition revealed the phenotypic variations under stress conditions, but the heat stress induced similar cell behavior. In parallel with developing the bioinformatics analysis pipeline, I also mapped a Hsp90-buffered phenotype via the bulk sergeant analysis. Five loci were contributed to the Hsp90-buffered phenotype. In this study, I demonstrated a common strategy for cells to quickly adapt to the changing environments via the Hsp90-regulated phenotypic diversification.

並列關鍵字

Hsp90 ； genetic buffering ； potentiator ； transcription regulation ； phenotypic plasticity

參考文獻

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