Functions of a newly identified meiotic protein, SCML1, and a meiosis-specific nuclear structure, the dense-body, in mice

减数分裂从二倍体生殖细胞产生单倍体配子，从而为哺乳动物的有性生殖提供基础。单倍体配子的产生依赖于减数分裂特异性的染色体行为和蛋白质表达的调控。为了获得新的见解单倍体配子产生的分子基础，我们筛选减数分裂蛋白质的潜在作用，在必要的减数分裂特异性过程。其中，我们的筛选发现了一种新的减数分裂蛋白，我们将其鉴定为以前未被识别的人SCML 1的小鼠直系同源物，这是一种功能未知的蛋白质。小鼠SCML 1是减数分裂特异性RNA丰富的核结构致密体（DB）的组成部分。DBs在哺乳动物（包括人类）的第一次减数分裂前期形成。虽然DB的组成和功能仍然是个谜，但最近的发现表明DB可能在减数分裂的关键方面发挥作用，例如小的非编码RNA（small noncoding RNA，smRNA）生物学和精母细胞减数分裂性染色体沉默。因此，我们建议通过SCML 1的分析来解决减数分裂DB的功能。我们将通过分析Scml 1基因敲除小鼠的减数分裂和配子发生来研究SCML 1的功能，Scml 1基因敲除小鼠将从我们最近生产的携带条件性敲除Scml 1等位基因的小鼠品系中产生。特别是，我们将解决假定的作用SCML 1在减数分裂的小RNA代谢和/或转座子沉默和性染色体沉默。后两者是与减数分裂smRNA生物学相关的基本减数分裂过程。此外，我们计划纯化DBs/SCML 1含有RNA-蛋白质复合物，以鉴定和表征在DBs中积累的蛋白质和RNA种类。这将是相关的了解的作用，DB在减数分裂RNA生物学。作为这些实验的一部分，我们将比较野生型和显示smRNA代谢异常的减数分裂突变体中含有SCML 1的RNA-蛋白质复合物的RNA组成（例如：Mili和Miwi突变体）。此外，我们将使用酵母双杂交和生物化学方法来鉴定和表征SCML 1蛋白质相互作用，并研究SCML 1介导的DB样结构形成的分子基础，我希望这些实验将揭示SCML 1和DB在减数分裂中的功能，并将使我们能够更好地了解DBs在减数分裂smRNA生物学和相关过程中的机制作用。这些实验也可能会影响我们对人类生殖健康的理解，因为smRNAs被认为可以保护生殖系免受转座子的侵害，并在配子发生过程中发挥重要作用。

Meiosis produces haploid gametes from diploid germ cells, thereby providing the basis for sexual reproduction in mammals. Generation of haploid gametes depends on meiosis-specific features of chromosome behaviour and regulation of protein expression. To gain novel insights into the molecular basis of haploid gamete generation, we screened for meiotic proteins with a potential role in essential meiosis-specific processes. Among others, our screen discovered a novel meiotic protein, which we identified as the previously unrecognized mouse orthologue of human SCML1, a protein of unknown function. Mouse SCML1 is a component of a meiosis-specific RNA-rich nuclear structure, the dense-body (DB). DBs form during the first meiotic prophase in mammals, including humans. Although the composition and the functions of the DB remain enigmatic, recent discoveries indicate possible functions for DBs in crucial aspects of meiosis, such as small non-coding RNA (smRNA) biology and meiotic sex chromosome silencing in spermatocytes.Our results show that ectopically expressed SCML1 builds DB-like structures in somatic cells, indicating that SCML1 might be a structural component of DBs. Therefore, we propose to address the functions of the meiotic DB through the analysis of SCML1. We will investigate the functions of SCML1 by analysing meiosis and gametogenesis in Scml1 knockout mice, which will be generated from our recently produced mouse-strain that carries a conditional knockout Scml1 allele. In particular, we will address putative roles of SCML1 in meiotic smRNA metabolism and/or in transposon silencing and sex chromosome silencing. The latter two are essential meiotic processes that have been linked to meiotic smRNA biology. Furthermore, we plan to purify DBs/SCML1 containing RNA-protein complexes, to identify and characterize proteins and RNA species that accumulate in DBs. This will be relevant for understanding the role of DBs in meiotic RNA biology. As part of these experiments, we will compare the RNA composition of SCML1 containing RNA-protein complexes in wildtype and in meiotic mutants that display abnormalities in smRNA metabolism (e.g.: Mili and Miwi mutants). In addition, we will use yeast-two hybrid and biochemical approaches to identify and characterize SCML1 protein interactions and to examine the molecular basis of SCML1-mediated formation of DB-like structures.I expect that these experiments will reveal SCML1 and DB functions in meiosis, and will allow us to better understand the mechanistic role of DBs in meiotic smRNA biology and related processes. These experiments will also likely impact on our understanding of human reproductive health, since smRNAs are believed to safeguard the germline from transposons and play essential roles during gametogenesis.