Mitochondrial small ribosomal RNA is a component of germinal granules in Xenopus embryos

Mitochondrial large rRNA (mtlrRNA) and small rRNA (mtsrRNA) have been identified as components of germinal granules in Drosophila. We have previously reported that mtlrRNA is present on the germinal granules in Xenopus embryos. Here we report that mtsrRNA is also a common component of the germinal granules. Extra-mitochondrial mtsrRNA is localized on the surface of germinal granules in germ plasm from four-cell to blastula stage, then disappears until the completion of gastrulation. This temporal and spatial distribution pattern is identical to that of mtlrRNA. During the stages when both mitochondrial rRNAs are present around the germinal granules, mitochondrial-type ribosomes, typified by their smaller size, were also present on the surface of the germinal granules.