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Many X-linked microRNAs escape meiotic sex chromosome inactivation

Rui Song, Seungil Ro, Jason D Michaels, Chanjae Park, John R McCarrey and Wei Yan

Nature Genetics 41 (4): 488-93, April 2009.
doi:10.1038/ng.338

This week’s succinct summary and analysis provided by Anonymous:

Meiotic sex chromosome inactivation (MSCI) is a process that silences unsynapsed chromosomes during meiosis, specifically the X and Y chromosomes in males.  While the reasons for this silencing are not understood, it has been postulated that MSCI prevents genomic instability.  Following up on previously published observations, Song et al. investigated whether X-linked miRNA genes escape silencing.   Carrying out a real-time PCR-based survey of X-linked miRNAs, the authors found that numerous miRNAs were upregulated transcriptionally during stages of spermatogenesis in which MSCI is expected to function, suggesting a major distinction between transcriptional regulation of miRNAs and mRNAs.

This report systematically investigates all X-linked miRNAs in various stages of spermatogenesis, checks their transcriptional regulation to verify that increased levels are not due simply to increased stability of miRNAs transcribed prior to MSCI, and follows up on a few miRNAs in more detail using in situ hybridization.  One weakness of the study, however, is that absolute miRNA expression levels were not determined. Therefore, although a miRNA may be upregulated, it is unclear whether this upregulation results in  (1) full or only a fractional escape from MSCI, and (2) a biologically active concentration of miRNA.   Nevertheless, this study provides an interesting starting point to investigate differential regulation during MSCI.