Numerical data underlying graphs.

The self-renewal and differentiation of germline stem cells (GSCs) are tightly regulated during oogenesis. The Drosophila female germline provides a powerful model to study these regulatory mechanisms. We previously identified Sakura (also known as Bourbon/CG14545) as a crucial factor for maintenance and differentiation of GSCs and oogenesis, and demonstrated that Sakura binds to Ovarian Tumor (Otu), another essential regulator of these processes. Here, we identify MYCBP (c-Myc binding protein) as an additional essential component of this regulatory network. We show that MYCBP physically associates with itself, Sakura, and Otu, forming binary and ternary complexes including a MYCBP•Sakura•Otu complex. MYCBP is highly expressed in the ovary, and mycbp null mutant females exhibit rudimentary ovaries with germline-less and tumorous ovarioles, fail to produce eggs, and are completely sterile. Germline-specific depletion of mycbp disrupts Dpp/BMP signaling, causing aberrant expression of bag-of-marbles (bam) and leading to defective differentiation and GSC loss. In addition, mycbp is required for female-specific splicing of sex-lethal (sxl), a master regulator of sex identity determination. These phenotypes closely resemble those observed in sakura and otu mutants. Together, our findings reveal that MYCBP functions in concert with Sakura and Otu to coordinate self-renewal and differentiation of GSCs and oogenesis in Drosophila.

卵子发生过程中，生殖系干细胞（germline stem cells, GSCs）的自我更新与分化受到严格调控。果蝇（Drosophila）雌性生殖系是研究此类调控机制的理想模型。我们此前已鉴定出Sakura（亦称Bourbon/CG14545）为维持生殖系干细胞自我更新、分化及卵子发生的关键因子，并证实Sakura可与卵巢肿瘤蛋白（Ovarian Tumor, Otu）结合——后者亦是此类过程的核心调控因子。本研究中，我们鉴定出c-Myc结合蛋白（MYCBP, c-Myc binding protein）为该调控网络的另一关键组分。研究发现，MYCBP可发生自身相互作用，并与Sakura和Otu形成二元及三元复合物，其中包含MYCBP•Sakura•Otu三元复合物。MYCBP在卵巢中高表达，mycbp纯合缺失突变的雌性果蝇卵巢发育不全，生殖系缺失且卵巢管呈肿瘤样增生，无法产生卵子，完全不育。生殖系特异性敲低mycbp会破坏Dpp/BMP信号通路，导致大理石盒基因（bag-of-marbles, bam）表达异常，进而引发分化缺陷及生殖系干细胞丢失。此外，mycbp对于性别致死基因（sex-lethal, sxl）的雌性特异性剪接是必需的，而sxl是性别身份决定的核心调控因子。上述表型与sakura及otu突变体中观察到的表型高度相似。综上，本研究结果表明，MYCBP可与Sakura及Otu协同作用，调控果蝇生殖系干细胞的自我更新、分化以及卵子发生过程。