A translation control module coordinates germline stem cell differentiation with ribosome biogenesis during Drosophila oogenesis [rRNA_RIP-seq]. A translation control module coordinates germline stem cell differentiation with ribosome biogenesis during Drosophila oogenesis [rRNA_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: Total RNA-seq of triplicate samples of ovaries expressing FLAG-tagged versions of Aramis, Athos, or Porthos 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（ribosomopathy）的疾病。目前学界尚未完全阐明核糖体水平如何调控干细胞分化。本研究中，我们发现三种RNA解旋酶对于核糖体生物发生以及果蝇卵子发生均不可或缺。我们将这三种解旋酶命名为阿拉米斯（Aramis）、阿托斯（Athos）与波托斯（Porthos），它们的缺失会导致p53异常稳定、细胞周期阻滞以及生殖干细胞（GSC）分化停滞。出乎意料的是，阿拉米斯对于一类带有5'末端寡聚嘧啶（5'-Terminal-Oligo-Pyrimidine, TOP）基序的mRNA群体的高效翻译必不可少，这类mRNA包括编码核糖体蛋白以及保守型p53抑制剂——新型核仁蛋白1（Novel Nucleolar protein 1, Non1）的转录本。TOP基序在哺乳动物中可协同调控生长相关mRNA的翻译。与哺乳动物系统类似，在果蝇卵子发生过程中，La相关蛋白同样可协同调控携带TOP基序的RNA的翻译。综上，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耦联起来。

整体实验设计：对分别表达FLAG标签融合的阿拉米斯、阿托斯或波托斯的卵巢样本进行三次生物学重复的总RNA测序；实验采用抗FLAG抗体进行RNA免疫沉淀，以IgG作为阴性对照，同时留存10%的裂解液作为输入样本。