miRNA and piRNA localization in the male mammalian meiotic nucleus.

During mammalian meiosis, transcriptional silencing of the XY bivalent is a necessary event where defects may lead to infertility in males. While not well understood, the mechanism of meiotic gene silencing is believed to be RNA-dependent. In this study, we investigated the types and localization of non-coding RNAs in the meiotic nucleus of the male mouse using a microarray screen with different cell isolates as well as FISH. We report that the dense body, a component of the murine spermatocyte sex body similar to that of a dense body in Chinese hamster spermatocytes, is DNA-negative but rich in proteins and RNA including miRNAs (micro RNAs) and piRNAs (PIWI associated small RNAs), or their precursors. Selective miRNAs and piRNAs localize to chromosome cores, telomeres and the sex body of spermatocytes. These RNAs have not previously been detected in meiotic nuclei. These RNAs appear to associate with the nucleolus of the Sertoli cells as well as with the dense body. While in MIWI-null male mice the nucleolar signal from miRNA and piRNA probes in Sertoli cells is largely diminished, a differential regulation must exist in meiotic nuclei since the localization of these two components appears to be unaffected in the null animal.