MSL3 coordinates a transcriptional and translational meiotic program in female Drosophila

Gamete formation from germline stem cells (GSCs) is essential for sexual reproduction. However, the regulation of GSC differentiation and meiotic entry are incompletely understood. Set2, which deposits H3K36me3 modifications, is required for differentiation of GSCs during Drosophila oogenesis. We discovered that the H3K36me3 reader Male-specific lethal 3 (MSL3) and the histone acetyltransferase complex Ada2a-containing (ATAC) cooperate with Set2 to regulate entry into meiosis in female Drosophila. MSL3 expression is restricted to the mitotic and early meiotic stages of the female germline, where it promotes transcription of genes encoding synaptonemal complex components and a germline enriched ribosomal protein S19 paralog, RpS19b. RpS19b upregulation is required for translation of Rbfox1, a known meiotic cell cycle entry factor. Thus, MSL3 is a master regulator of meiosis, coordinating the expression of factors required for recombination and GSC differentiation. We find that MSL3 is expressed during mouse spermatogenesis, suggesting a conserved function during meiosis. Overall design: Ovary mRNA profiles of 1-5-day old control flies (hsbam, samples 1-2) were compared to experimental flies (MSL3 RNAi and NC2b RNAi, samples 7-10). Ovary mRNA profiles of 1-5-day old control flies (hsbam, samples 3-4) were compared to experimental flies (Set2 RNAi, samples 5-6).Ovary mRNA profiles of 1-5-day old control flies (bam RNAi, samples 11-12) were compared to experimental flies (bam RNAi;S19b mutant, samples 13-14). Ovary profiles of total mRNA and polysome-enriched mRNA from 1-5-day old control flies (hsbam_T and hsbam_P, samples 15-18) were compared to experimental flies (S19b RNAi_T and S19b_P; samples 19-22). Ovary profiles of 1-5 day old wild type flies (Whole_Ovaries, sample 23) were used for reference of developmental staging of samples. Ovary profiles were generated by deep sequencing, in singlet (sample 23) or duplicate (samples 1-2, 3-4, 5-6, 7-8, 9-10, 11-12, 13-14, 15 and 17, 16 and 18, 19 and 21, 20 and 22) using Illumina NextSeq500.