RNA helicase Belle (DDX3) non-autonomously suppresses germ cell tumorigenesis in the testes of Drosophila via regulation of multiple mRNAs

DEAD-box RNA helicases DDX3 are important developmental regulators of multiple aspects of RNA metabolism of eukaryotes. belle, a single DDX3 ortholog in Drosophila, is essential for fly viability, fertility, and germline stem cell maintenance. Here we showed that RNAi belle knockdown in testis cyst cells caused a disruption of adhesion between germ cells and cyst cells and a generation of tumor-like clusters of stem-like germ cells. Ectopic expression of β-integrin in cyst cells rescued early stages of spermatogenesis in the belle knockdown testes, indicating that integrin adhesion complexes are required for interaction between somatic and germ cells in cyst. To address in details Belle functions in spermatogenesis we performed CLIP-seq analysis and identified multiple mRNAs which interacted with Belle in the testes. A set of Belle targets includes mRNAs of factors that are essential for preventing tumor-like cluster formation of early germ cells and ensuring of sustained gametogenesis.

DEAD-box RNA解旋酶DDX3是调控真核生物RNA代谢多个方面的重要发育调控因子。果蝇体内唯一的DDX3同源基因belle，对果蝇的存活能力、生育力以及生殖系干细胞的维持均至关重要。本研究证实，在睾丸囊细胞中敲低belle的表达，会破坏生殖细胞与囊细胞间的黏附连接，并催生干细胞样生殖细胞形成肿瘤样簇。在囊细胞中异位表达β整合素（β-integrin），可挽救belle敲低果蝇睾丸中精子发生的早期阶段，这表明整合素黏附复合物对于囊结构中体细胞与生殖细胞的相互作用是必需的。为深入解析Belle在精子发生中的功能，我们开展了紫外交联免疫沉淀结合测序（CLIP-seq）分析，鉴定出了睾丸内与Belle相互作用的多种信使RNA（mRNA）。Belle的靶标集合涵盖了一系列关键因子的mRNA，这些因子对于阻止早期生殖细胞形成肿瘤样簇、保障持续配子发生均不可或缺。