Kashikawa M, Amikura R, Nakamura A, Kobayashi S
Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
Dev Growth Differ. 1999 Aug;41(4):495-502. doi: 10.1046/j.1440-169x.1999.00451.x.
In Drosophila, formation of the germline progenitors, the pole cells, is induced by polar plasm localized in the posterior pole region of early embryos. The polar plasm contains polar granules, which act as a repository for the factors required for pole cell formation. It has been postulated that the factors are stored as mRNA and are later translated on polysomes attached to the surface of polar granules. Here, the identification of mitochondrial small ribosomal RNA (mtsrRNA) as a new component of polar granules is described. The mtsrRNA was enriched in the polar plasm of the embryos immediately after oviposition and remained in the polar plasm throughout the cleavage stage until pole cell formation. In situ hybridization at an ultrastructural level revealed that mtsrRNA was enriched on the surface of polar granules in cleavage embryos. Furthermore, the localization of mtsrRNA in the polar plasm depended on the normal function of oskar, vasa and tudor genes, which are all required for pole cell formation. The temporal and spatial distribution of mtsrRNA is essentially identical to that of mitochondrial large ribosomal RNA (mtlrRNA), which has been shown to be required for pole cell formation. Taken together, it is speculated that mtsrRNA and mtlrRNA are part of the translation machinery localized to polar granules, which is essential for pole cell formation.
在果蝇中，生殖系祖细胞即极细胞的形成是由早期胚胎后极区域定位的极质诱导的。极质包含极颗粒，其作为极细胞形成所需因子的储存库。据推测，这些因子以mRNA形式储存，随后在附着于极颗粒表面的多核糖体上进行翻译。在此，描述了线粒体小核糖体RNA（mtsrRNA）作为极颗粒新成分的鉴定。产卵后，mtsrRNA在胚胎的极质中富集，并在整个卵裂阶段一直保留在极质中，直至极细胞形成。超微结构水平的原位杂交显示，mtsrRNA在卵裂胚胎的极颗粒表面富集。此外，mtsrRNA在极质中的定位取决于osk、vasa和tudor基因的正常功能，这些基因都是极细胞形成所必需的。mtsrRNA的时空分布与线粒体大核糖体RNA（mtlrRNA）基本相同，mtlrRNA已被证明是极细胞形成所必需的。综上所述，推测mtsrRNA和mtlrRNA是定位于极颗粒的翻译机制的一部分，这对极细胞形成至关重要。
