Amikura R, Kashikawa M, Nakamura A, Kobayashi S
Institute of Biological Sciences, Gene Experiment Center, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
Proc Natl Acad Sci U S A. 2001 Jul 31;98(16):9133-8. doi: 10.1073/pnas.171286998. Epub 2001 Jul 24.
Mitochondrially encoded large and small ribosomal RNAs (mtlrRNA and mtsrRNA) are transported out of mitochondria to polar granules, the distinctive organelles of germ plasm in Drosophila. Reduction of the extramitochondrial mtlrRNA amount leads to the failure of embryos to form the germ-line progenitors, or pole cells, suggesting that mtlrRNA, along with mtsrRNA, functions on the polar granules to specify the germ line. In this study, we provide several lines of evidence showing that there are mitochondria-type ribosomes on the polar granules during a short period before pole cell formation. Our ultrastructural analysis reveals that these ribosomes include both mitochondrial rRNAs and at least two mitochondrial ribosomal proteins (S12 and L7/L12). Furthermore, these ribosomes are integrated into well developed polysomes on the surface of polar granules. We propose that translation dependent on mitochondria-type ribosomes is an important mechanism underlying germ-line formation.
线粒体编码的大、小核糖体RNA（mtlrRNA和mtsrRNA）从线粒体转运至极性颗粒，极性颗粒是果蝇生殖质中的独特细胞器。线粒体外mtlrRNA量的减少导致胚胎无法形成生殖系祖细胞或极细胞，这表明mtlrRNA与mtsrRNA一起在极性颗粒上发挥作用以确定生殖系。在本研究中，我们提供了几条证据表明在极细胞形成前的短时间内极性颗粒上存在线粒体类型的核糖体。我们的超微结构分析显示这些核糖体既包含线粒体rRNA，也至少包含两种线粒体核糖体蛋白（S12和L7/L12）。此外，这些核糖体整合到极性颗粒表面发育良好的多核糖体中。我们提出依赖线粒体类型核糖体的翻译是生殖系形成的重要机制。
