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Fig. 7 Meioc was required for upregulation of 28S rRNA. (A) Expression pattern of 28S rRNA in isolated sox17::egfp spermatogonia, based on the amount of Meioc granules and the localization. Right panels are intensities of 28S rRNA for each class of the purified sox17::egfp spermatogonia. 51≤C and N: 51≤cytoplasmic and nuclear Meioc granules, respectively. *p<0.05, **p<0.01, n: number of analyzed spermatogonia. Scale bars: 10 µm. (B) Expression patterns of Piwil1 in five classes of Meioc-expressing spermatogonia in testis sections. The graph shows intensities of Piwil1 in wild-type testes sections for each class of the spermatogonia. The characteristic large nucleoli of spermatogonial stem cells (SSCs) were identified based on nucleolar voids observed in DAPI staining. Arrows: Piwil1 detectable nucleoli; arrowheads: Piwil1 undetectable nucleoli. 51≤C and N: 51≤cytoplasmic and nuclear Meioc granules, respectively. **p<0.01. Scale bars: 10 µm. (C) Graphical abstract. Meioc prevents the nucleolar localization of Piwil1 and its associated Setdb1 and HP1α to upregulate rRNA transcripts that are required for zebrafish SSCs to differentiate.