A translation control module coordinates germline stem cell differentiation with ribosome biogenesis during Drosophila oogenesis [mRNA_RIP-seq]

Ribosomal defects perturb stem cell differentiation, causing diseases called ribosomopathies. How ribosome levels control stem cell differentiation is not fully known. Here, we discovered three RNA helicases are required for ribosome biogenesis and for Drosophila oogenesis. Loss of these helicases, which we named Aramis, Athos and Porthos, lead to aberrant stabilization of p53, cell cycle arrest and stalled GSC differentiation. Unexpectedly, Aramis is required for efficient translation of a cohort of mRNAs containing a 5'-Terminal-Oligo-Pyrimidine (TOP)-motif, including mRNAs that encode ribosomal proteins and a conserved p53 inhibitor, Novel Nucleolar protein 1 (Non1). The TOP-motif co-regulates the translation of growth-related mRNAs in mammals. As in mammals, the La-related protein co-regulates the translation of TOP-motif containing RNAs during Drosophila oogenesis. Thus, a previously unappreciated TOP-motif in Drosophila responds to reduced ribosome biogenesis to co-regulate the translation of ribosomal proteins and a p53 repressor, thus coupling ribosome biogenesis to GSC differentiation. Overall design: mRNA-seq of triplicate samples of ovaries expressing FLAG-tagged Larp subjected to RNA immunoprecipitation using anti-FLAG antibody or IgG as a negative control, with 10% of lysate reserved for input.

核糖体缺陷会扰乱干细胞分化，引发一类被称为核糖体病（ribosomopathies）的疾病。目前，核糖体水平如何调控干细胞分化尚未完全阐明。本研究发现，三种RNA解旋酶（RNA helicases）是核糖体生物发生与果蝇卵子发生过程所必需的。我们将这些解旋酶命名为阿拉米斯（Aramis）、阿托斯（Athos）与波托斯（Porthos）；敲除这些解旋酶会导致p53异常稳定、细胞周期阻滞以及生殖干细胞（GSC）分化受阻。出乎意料的是，阿拉米斯对于一组携带5'末端寡嘧啶（TOP）基序的mRNA的高效翻译不可或缺，这类mRNA包括编码核糖体蛋白以及保守p53抑制剂——新型核仁蛋白1（Non1）的转录本。TOP基序可协同调控哺乳动物中生长相关mRNA的翻译。与哺乳动物一致，果蝇卵子发生过程中，La相关蛋白（La-related protein）同样可协同调控携带TOP基序的RNA的翻译。由此可见，果蝇中此前未被认知的TOP基序可响应核糖体生物发生水平的降低，协同调控核糖体蛋白与p53阻遏物的翻译，从而将核糖体生物发生与生殖干细胞分化过程相偶联。实验整体设计：对表达FLAG标签化Larp的卵巢组织的三联重复样本进行mRNA测序；实验采用抗FLAG抗体或免疫球蛋白G（IgG）作为阴性对照进行RNA免疫沉淀，同时留存10%的裂解液作为输入对照。