Nguyen Chi Mai, Chalmel Frédéric, Agius Eric, Vanzo Nathalie, Khabar Khalid S A, Jégou Bernard, Morello Dominique
CBD, CNRS UMR5547, IFR 109, Université Paul Sabatier, Toulouse, France.
PLoS One. 2009;4(3):e4900. doi: 10.1371/journal.pone.0004900. Epub 2009 Mar 31.
In mammals, a temporal disconnection between mRNA transcription and protein synthesis occurs during late steps of germ cell differentiation, in contrast to most somatic tissues where transcription and translation are closely linked. Indeed, during late stages of spermatogenesis, protein synthesis relies on the appropriate storage of translationally inactive mRNAs in transcriptionally silent spermatids. The factors and cellular compartments regulating mRNA storage and the timing of their translation are still poorly understood. The chromatoid body (CB), that shares components with the P. bodies found in somatic cells, has recently been proposed to be a site of mRNA processing. Here, we describe a new component of the CB, the RNA binding protein HuR, known in somatic cells to control the stability/translation of AU-rich containing mRNAs (ARE-mRNAs).
METHODOLOGY/PRINCIPAL FINDINGS: Using a combination of cell imagery and sucrose gradient fractionation, we show that HuR localization is highly dynamic during spermatid differentiation. First, in early round spermatids, HuR colocalizes with the Mouse Vasa Homolog, MVH, a marker of the CB. As spermatids differentiate, HuR exits the CB and concomitantly associates with polysomes. Using computational analyses, we identified two testis ARE-containing mRNAs, Brd2 and GCNF that are bound by HuR and MVH. We show that these target ARE-mRNAs follow HuR trafficking, accumulating successively in the CB, where they are translationally silent, and in polysomes during spermatid differentiation.
CONCLUSIONS/SIGNIFICANCE: Our results reveal a temporal regulation of HuR trafficking together with its target mRNAs from the CB to polysomes as spermatids differentiate. They strongly suggest that through the transport of ARE-mRNAs from the CB to polysomes, HuR controls the appropriate timing of ARE-mRNA translation. HuR might represent a major post-transcriptional regulator, by promoting mRNA storage and then translation, during male germ cell differentiation.
在哺乳动物中，与大多数转录和翻译紧密相连的体细胞组织不同，生殖细胞分化后期会出现mRNA转录与蛋白质合成之间的时间脱节。实际上，在精子发生后期，蛋白质合成依赖于翻译无活性的mRNA在转录沉默的精子细胞中的适当储存。调节mRNA储存及其翻译时间的因素和细胞区室仍知之甚少。类染色质体（CB）与体细胞中的P小体共享成分，最近被认为是mRNA加工的场所。在这里，我们描述了CB的一个新成分，RNA结合蛋白HuR，在体细胞中已知其可控制富含AU的mRNA（ARE-mRNA）的稳定性/翻译。
方法/主要发现：通过细胞成像和蔗糖梯度分级分离相结合的方法，我们表明HuR在精子细胞分化过程中的定位高度动态。首先，在早期圆形精子细胞中，HuR与CB的标志物小鼠Vasa同源物MVH共定位。随着精子细胞的分化，HuR离开CB并同时与多核糖体结合。通过计算分析，我们鉴定出两个睾丸中含ARE的mRNA，即Brd2和GCNF，它们与HuR和MVH结合。我们表明这些靶ARE-mRNA跟随HuR的运输，在精子细胞分化过程中依次在CB中积累，在那里它们是翻译沉默的，然后在多核糖体中积累。
结论/意义：我们的结果揭示了随着精子细胞的分化，HuR及其靶mRNA从CB到多核糖体的时间调节。它们强烈表明，通过将ARE-mRNA从CB运输到多核糖体，HuR控制ARE-mRNA翻译的适当时间。在雄性生殖细胞分化过程中，HuR可能通过促进mRNA储存然后翻译，代表一种主要的转录后调节因子。
