Campbell Anne C, Updike Dustin L
Kathryn W. Davis Center for Regenerative Biology and Medicine, Mount Desert Island Biological Laboratory, Bar Harbor, ME 04672, USA.
Kathryn W. Davis Center for Regenerative Biology and Medicine, Mount Desert Island Biological Laboratory, Bar Harbor, ME 04672, USA
Development. 2015 May 15;142(10):1745-55. doi: 10.1242/dev.121434.
Germ granules (P granules) in C. elegans are required for fertility and function to maintain germ cell identity and pluripotency. Sterility in the absence of P granules is often accompanied by the misexpression of soma-specific proteins and the initiation of somatic differentiation in germ cells. To investigate whether this is caused by the accumulation of somatic transcripts, we performed mRNA-seq on dissected germlines with and without P granules. Strikingly, we found that somatic transcripts do not increase in the young adult germline when P granules are impaired. Instead, we found that impairing P granules causes sperm-specific mRNAs to become highly overexpressed. This includes the accumulation of major sperm protein (MSP) transcripts in germ cells, a phenotype that is suppressed by feminization of the germline. A core component of P granules, the endo-siRNA-binding Argonaute protein CSR-1, has recently been ascribed with the ability to license transcripts for germline expression. However, impairing CSR-1 has very little effect on the accumulation of its mRNA targets. Instead, we found that CSR-1 functions with P granules to prevent MSP and sperm-specific mRNAs from being transcribed in the hermaphrodite germline. These findings suggest that P granules protect germline integrity through two different mechanisms, by (1) preventing the inappropriate expression of somatic proteins at the level of translational regulation, and by (2) functioning with CSR-1 to limit the domain of sperm-specific expression at the level of transcription.
秀丽隐杆线虫中的生殖颗粒（P颗粒）对于生育能力是必需的，其功能是维持生殖细胞的特性和多能性。在没有P颗粒的情况下出现的不育现象，常常伴随着体细胞特异性蛋白的错误表达以及生殖细胞中体细胞分化的启动。为了研究这是否是由体细胞转录本的积累所导致的，我们对有和没有P颗粒的分离生殖系进行了mRNA测序。令人惊讶的是，我们发现在年轻成虫的生殖系中，当P颗粒受损时，体细胞转录本并没有增加。相反，我们发现P颗粒受损会导致精子特异性mRNA高度过表达。这包括生殖细胞中主要精子蛋白（MSP）转录本的积累，这种表型会因生殖系的雌性化而受到抑制。P颗粒的一个核心成分，即结合内源性小干扰RNA的AGO蛋白CSR-1，最近被认为具有许可转录本进行生殖系表达的能力。然而，破坏CSR-1对其mRNA靶标的积累影响很小。相反，我们发现CSR-1与P颗粒共同作用，以防止MSP和精子特异性mRNA在雌雄同体的生殖系中被转录。这些发现表明，P颗粒通过两种不同的机制保护生殖系的完整性，一是（1）在翻译调控水平上防止体细胞蛋白的不适当表达，二是（2）与CSR-1共同作用，在转录水平上限制精子特异性表达的范围。
