Tudor-domain containing protein 5-like promotes male sexual identity in the Drosophila germline and is repressed in females by Sex lethal. Tudor-domain containing protein 5-like promotes male sexual identity in the Drosophila germline and is repressed in females by Sex lethal

Like humans, all sexually reproducing organisms require gametes to reproduce. Gametes are made by specialized cells called germ cells, which must have the correct sexual identity information to properly make sperm or eggs. In fruit flies, germ cell sexual identity is controlled by the RNA-binding protein Sxl, which is expressed only in females. To better understand how Sxl promotes female identity, we conducted an RNA expression profiling experiment to identify genes whose expression changes in response to the loss of Sxl from germ cells. Here, we identify Tudor domain containing protein 5-like (Tdrd5l), which is expressed 17-fold higher in ovaries lacking Sxl compared to control ovaries. Additionally, Tdrd5l plays an important role in males as male flies that are mutant for this gene cannot make sperm properly and thus are less fertile. Moreover, we find that Tdrd5l promotes male identity in the germline, as several experiments show that it can shift the germ cell developmental program from female to male. This study tells us that Sxl promotes female identity in germ cells by repressing genes, like Tdrd5l, that promote male identity. Future studies into the function of Tdrd5l will provide mechanistic insight into how this gene promotes male identity Overall design: gene expression comparrison between bam male and female flies. Expression analysis was also conducted between Sxl RNAi females and mcherry RNAi females in a bam mutant backgrounds

如同人类，所有进行有性生殖的生物体均需配子（gamete）完成繁殖过程。配子由一类被称为生殖细胞（germ cell）的特化细胞产生，这类细胞必须携带准确的性别身份信息，方可正常生成精子或卵子。在果蝇中，生殖细胞的性别身份由RNA结合蛋白Sxl（RNA-binding protein Sxl）调控，该蛋白仅在雌性个体中表达。
为深入解析Sxl如何促进生殖细胞的雌性身份确立，我们开展了RNA表达谱分析（RNA expression profiling）实验，以筛选出在生殖细胞中缺失Sxl后表达水平发生改变的基因。本研究鉴定出含Tudor结构域蛋白5样蛋白（Tudor domain containing protein 5-like，Tdrd5l）：相较于对照卵巢，该基因在缺失Sxl的卵巢中表达量高17倍。
此外，Tdrd5l在雄性个体中同样发挥关键功能：携带该基因突变的雄性果蝇无法正常生成精子，因此育性显著下降。进一步研究发现，Tdrd5l可促进生殖系的雄性身份，多项实验证实其能够将生殖细胞的发育程序从雌性向雄性转变。
本研究表明，Sxl通过抑制诸如Tdrd5l这类促进雄性身份的基因，从而在生殖细胞中确立雌性身份。后续针对Tdrd5l功能的研究，将为解析该基因促进雄性身份的分子机制提供重要见解。
整体实验设计：对bam突变的雌雄果蝇开展基因表达比较分析。同时，在bam突变背景下，分别对Sxl RNA干扰（RNAi）雌性果蝇与mcherry RNA干扰（RNAi）雌性果蝇进行表达分析。