Fig. 5

Changes in mRNA stability and compartmentalization in Drosha-null spermatogenic cells. a Density plots showing the distribution of 3′ UTR length of RNP- or polysome-enriched mRNAs in Drosha-null pachytene spermatocytes (“RNP pachytene Drosha” or “Polysome pachytene Drosha” in upper panel)) and round spermatids (“RNP round Drosha” or “Polysome round Drosha” in lower panel). Boxplots in the insets show the average size of 3′ UTRs of RNP- and polysome-enriched mRNAs in Drosha-null pachytene spermatocytes (upper panel) and round spermatids (lower panel). Student’s t-test was performed. b Density plots showing the distribution of 3′ UTR length of polysome-enriched mRNAs in wild-type (WT) or Drosha-null pachytene spermatocytes (upper panel) and round spermatids (lower panel). Boxplots in the insets demonstrate the average 3′ UTR size in polysome-enriched mRNAs in wild-type and Drosha-null pachytene spermatocytes (upper panel) and round spermatids (lower panel). Student’s t-test was performed. c Heatmap showing levels of RNP- and polysome-enriched mRNAs in wild-type or Drosha-null pachytene spermatocytes and round spermatids. d Changes in expression patterns and cytoplasmic compartmentalization of multiple isoforms of three genes (Tdrd5, Apc, and Fkbp6) in the RNP and polysome fractions in pachytene spermatocytes and round spermatids. e The proposed mechanism through which miRNAs control mRNA compartmentalization by recruiting shorter 3′ UTR transcripts into the RNPs and removing longer 3′ UTR transcripts from the RNPs. In pachytene spermatocytes, RNP-enriched mRNAs generally have shorter 3′ UTRs than polysome-enriched mRNAs, and the RNP-enriched mRNAs are associated with RNP-enriched miRNAs at sites proximal to the stop codon in 3′ UTRs, whereas polysome-enriched mRNAs tend to be bound by miRNAs at sites distal from the stop codon in the 3′ UTRs. When pachytene spermatocytes develop into round spermatids, new miRNAs are produced which recruit shorter 3′ UTR mRNAs into RNPs by binding the proximal sites; meanwhile, mRNAs containing distal binding sites, which are usually those with longer 3′ UTRs, are removed from RNPs. In this manner, the RNP fraction becomes gradually enriched with shorter 3′ UTR transcripts. When round spermatids develop into elongating spermatids, a significant proportion of RNP-enriched miRNAs shift out of RNPs and their target mRNAs also shift to polysomes for translation. Asterisks indicate statistically significant p values