The Drosophila RNase Z(L) (dRNaseZ) gene encodes a member of the ELAC1/ELAC2 protein family with homologs in every living organism. All RNase Z proteins tested so far were found to possess endoribonuclease activity, which is responsible for the removal of a 3' trailer from a primary tRNA transcript. Given that tRNA 3'-end processing has been delineated using in vitro, bacterial and cell culture models, its relevance to RNase Z functions in vivo has yet to be established. In this study, we employed heritable RNA interference (RNAi) in combination with the GAL4/UAS system to spatiotemporally knockdown the dRNaseZ gene and study its biological role in cells of a developing fruit fly. We found that dRNaseZ is an essential gene, as ubiquitous knockdown caused growth arrest and early larval lethality. Molecular analysis confirmed that dRNaseZ is necessary for 3'-end processing of nuclear and mitochondrial tRNAs: knockdown larvae displayed significant accumulation of both types of processing intermediates with extensions at the 3' end. This is the first in vivo demonstration of RNase Z(L) dependent tRNA processing in the context of a metazoan model organism. Using tissue-specific GAL4 drivers, we also showed that in mitotically growing imaginal discs dRNaseZ is required for cell proliferation and/or viability, but not for the maintenance of their differentiated progeny. In endoreplicating salivary glands, dRNaseZ controls organ size by supporting cell growth but not DNA replication. Although the mechanisms remain unclear, our results support the notion that RNase Z(L) is involved in biological pathways regulating cell growth and proliferation.

中文翻译：

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dRNaseZ的RNAi敲除是果蝇ELAC2的同源物，损害有丝分裂和内复制组织的生长。

果蝇RNase Z（L）（dRNaseZ）基因编码ELAC1 / ELAC2蛋白家族的一个成员，在每个活生物体中都有同源性。到目前为止，所有测试的RNase Z蛋白都具有内切核糖核酸酶活性，这是从初级tRNA转录物中去除3'尾区的原因。鉴于已经使用体外，细菌和细胞培养模型描述了tRNA 3'末端加工，因此尚未确定其与体内RNase Z功能的相关性。在这项研究中，我们将可遗传的RNA干扰（RNAi）与GAL4 / UAS系统结合使用，以时空敲除dRNaseZ基因并研究其在发育中的果蝇细胞中的生物学作用。我们发现dRNaseZ是必不可少的基因，因为普遍存在的敲低会导致生长停滞和早期幼虫致死率。分子分析证实，dRNaseZ对于核和线粒体tRNA的3'末端加工是必需的：敲除幼虫显示出两种加工中间体的大量积累，并在3'末端延伸。这是在后生动物模型体内，首次证实了依赖RNase Z（L）的tRNA加工。使用组织特异性GAL4驱动程序，我们还表明，在有丝分裂中生长的假想盘中，dRNaseZ是细胞增殖和/或生存力所必需的，而不是维持其分化后代所必需的。在唾液腺的内复制中，dRNaseZ通过支持细胞生长而不是DNA复制来控制器官大小。尽管机制尚不清楚，