研究線蟲中異質核醣蛋白HRP-2在let-7路徑中扮演的角色

Abstract

異質核糖核酸蛋白是目前已知會參與在RNA生合成的步驟中，包含轉錄、RNA剪接、運輸、轉譯以及降解。在過去幾年中，異質核糖核酸蛋白被發現會調控某些微小核醣核酸(miRNA)的生合成。微小核醣核酸是一群長度約為22個核甘酸長的non-coding RNA，主要是通過後轉錄階段結合在目標基因的3’ UTR上並且抑制轉譯以及促進mRNA的降解。其中，let-7為最早被發現的miRNA的一員，會在線蟲中透過降低lin-41的表現來控制幼蟲進入成蟲的轉換，LIN-41蛋白則是會抑制成蟲轉錄因子lin-29的表現。因此當let-7發生功能喪失突變時會無法抑制lin-41使得lin-29延後表現，進而引發發育遲緩的現象。目前已知在人類細胞中也有發現let-7抑制lin-41的現象，顯示這是一個具有高度保守性的發育基因調節機制，而let-7的缺失目前被發現與多種癌症有關。在本篇論文中，我發現利用RNA干擾降低異質核醣核酸蛋白HRP-2的表現後會抑制let-7部分功能喪失線蟲let-7(n2853)的表現型，包含seam cells終端分裂延後以及膠原蛋白COL-19表現下降; 跟COL-19是 lin-29下游直接控制的基因之一，所以COL-19::GFP常被用來研究let-7 。在lin-41獲得功能突變的線蟲lin-41(bx37) 中我發現降低HRP-2表現量會抑制seam cell細胞膜延後聚合的表現型在lin-29剔除線蟲lin-29(n333)中降低HRP-2的表現不會引響seam cells終端分裂延後。但是我發現在lin-29(n333)中降低HRP-2的表現能夠抑制膠原蛋白COL-19表現下降的表現型，而在實驗中身為negative control的lin-41 RNAi在抑制LIN-41的表現量後也能夠抑制COL-19表現下降的表現型，這有可能是COL-19基因也受到其他路徑的調控，但目前詳細機制並不清楚。在本篇論文中，我們認為HRP-2有可能影響let-7路徑，但是詳細的機制仍然需要更進一步的研究。

Heterogeneous nuclear ribonucleoproteins (hnRNPs) have been demonstrated to participate in most RNA metabolisms, including transcription, splicing, RNA transport, translation and RNA degradation. In the past few years, hnRNPs were also found in regulation of biogenesis and function of microRNAs(miRNAs). MicroRNAs are ~22 nt in length small non-coding RNAs that regulate gene expression by binding to the 3’ UTR of target mRNAs, then triggering translation repression and mRNA degradation. Among them, one of the founding members, let-7 regulates the larva-to-adult transition by inhibiting heterochronic gene lin-41. The LIN-41 protein repress expression of the adult specific transcription factor lin-29. let-7 loss-of-function usually result in retardation due to the inability to inhibit lin-41. The let-7 inhibiting lin-41 regulation has been demonstrated to be highly conserved from C. elegans to human. In human, dysregulations of let-7 frequently are associated with various types of cancers. Here, I found depletion of heterogeneous nuclear ribonucleoprotein HRP-2 by RNA interference suppressed the heterochronic phenotype caused by let-7(n2853), such as delayed terminal differentiation of seam cells, and collage protein COL-19 depressed. While depletion of HRP-2 could also suppressed delayed seam cell membrane fusion in lin41 gain of function strain lin-41(bx37). Depletion of HRP-2 could not suppressed delayed terminal differentiation of seam cells in lin-29 mutant strain lin-29(n333), but it can suppress collage protein COL-19 depressed, and the negative control of this experiment lin-41 RNAi can also suppress collage protein COL-19 depressed. To summarize, we consider HRP-2 may interact with let-7 pathway and further investigation is needed to determine the mechanism.