Kobayashi S, Amikura R, Mukai M
Institute of Biological Sciences, Gene Experiment Center, University ofTsukuba, Tsukuba, Ibaraki, 305-8572, Japan.
Curr Biol. 1998 Oct 8;8(20):1117-20. doi: 10.1016/s0960-9822(98)70466-x.
In Xenopus, factors with the ability to establish the germ line are localized in the vegetal pole cytoplasm, or germ plasm, of the early embryo [1-3]. The germ plasm of Xenopus, and of many other animal species including Drosophila, contains electron-dense germinal granules which may be essential for germ-line formation [4-5]. Several components of the germinal granules have so far been identified in Drosophila [6-10]. One of these is mitochondrial large ribosomal RNA (mtlrRNA), which is present in the germinal granules (polar granules) during the cleavage stage until the formation of the germ-line progenitors or pole cells [8-9]. MtlrRNA has been identified as a factor that induces pole cells in embryos that have been sterilized by ultraviolet radiation [11]. The reduction of mtlrRNA in germ plasm by injecting anti-mtlrRNA ribozymes into embryos leads to the inability of these embryos to form pole cells [12]. These observations clearly show that mtlrRNA is essential for pole cell formation in Drosophila. Here, we report that mtlrRNA is enriched in germ plasm of Xenopus embryos from the four-cell stage to the blastula. Furthermore, our electron microscopic studies show that this mtlrRNA is present in the germinal granules during these stages. Thus, mtlrRNA is a common component of germinal granules in Drosophila and Xenopus, suggesting that the mtlrRNA has a role in germ-line development across phylogenetic boundaries.
在非洲爪蟾中，具有建立生殖系能力的因子定位于早期胚胎的植物极细胞质或生殖质中[1-3]。非洲爪蟾以及包括果蝇在内的许多其他动物物种的生殖质含有电子致密的生殖颗粒，这可能对生殖系形成至关重要[4-5]。到目前为止，已在果蝇中鉴定出生殖颗粒的几种成分[6-10]。其中之一是线粒体大核糖体RNA（mtlrRNA），它在卵裂阶段直至生殖系祖细胞或极细胞形成期间存在于生殖颗粒（极颗粒）中[8-9]。MtlrRNA已被确定为一种能在经紫外线辐射绝育的胚胎中诱导极细胞形成的因子[11]。通过向胚胎中注射抗mtlrRNA核酶来降低生殖质中的mtlrRNA会导致这些胚胎无法形成极细胞[12]。这些观察结果清楚地表明，mtlrRNA对果蝇中极细胞的形成至关重要。在此，我们报告mtlrRNA在从四细胞期到囊胚期的非洲爪蟾胚胎的生殖质中富集。此外，我们的电子显微镜研究表明，在这些阶段该mtlrRNA存在于生殖颗粒中。因此，mtlrRNA是果蝇和非洲爪蟾生殖颗粒的共同成分，这表明mtlrRNA在跨系统发育界限的生殖系发育中起作用。
