The DNA/RNA-binding protein MSY2 marks specific transcripts for cytoplasmic storage in mouse male germ cells

During spermatogenesis, male germ cells temporally synthesize many proteins as they differentiate through meiosis and become spermatozoa. The germ cell Y-box protein, MSY2, constituting ≈0.7% of total protein in male germ cells, binds to a consensus promoter element, and shows a general lack of RNA-binding specificity. Combining immunoprecipitation and suppressive subtractive hybridization, we identified populations of germ cell mRNAs that are not bound or bound by MSY2. The former population is enriched in cell growth and ubiquitously expressed mRNAs, whereas the latter population is enriched for stored or translationally delayed, male gamete-specific transcripts. Chromatin precipitation assays reveal that most of the MSY2 target mRNAs are transcribed from genes containing the Y-box DNA-binding motif in their promoters. In transgenic mice, mRNAs encoding exogenous GFP are directed or not directed into the MSY2-bound fraction by promoters containing or lacking the Y-box motif, respectively. We propose that MSY2 marks specific mRNAs in the nucleus for cytoplasmic storage, thereby linking transcription and mRNA storage/ translational delay in meiotic and postmeiotic male germ cells of the mouse.