Msl3 promotes germline stem cell differentiation in female Drosophila

Abstract

Gamete formation from germline stem cells (GSCs) is essential for sexual reproduction. However, the regulation of GSC differentiation are incompletely understood. Set2, which deposits H3K36me3 modifications, is required for GSC differentiation during Drosophila oogenesis. We discovered that the H3K36me3 reader Male-specific lethal 3 (MSL3) and histone acetyltransferase complex Ada2a-containing (ATAC) cooperate with Set2 to regulate GSC differentiation in female Drosophila. MSL3, acting independent from the rest of the male specific lethal complex, promotes transcription of genes including a germline enriched ribosomal protein S19 paralog, RpS19b. RpS19b upregulation is required for translation of RNA-binding Fox protein 1 (Rbfox1), a known meiotic cell cycle entry factor. Thus, MSL3 regulates GSC differentiation by modulating translation of a key factor that promotes transition to an oocyte fate.

Oo-site: A dashboard to visualize gene expression during Drosophila oogenesis suggests meiotic entry is regulated post-transcriptionally

“…Our bulk RNA-seq data, as well as the available scRNA-seq data indicated that RpS19b was highly expressed in GSCs, decreased during differentiation in the cyst stages and was greatly decreased in expression in early egg chambers, consistent with previous reports ( Fig. 2 A,B) ( McCarthy et al, 2021 ; Sarkar et al, 2021 preprint). To further validate this expression pattern, we probed the expression of RpS19b in vivo using in situ hybridization as well as an RpS19b::GFP line that is under endogenous control elements ( McCarthy et al, 2021 ).…”

Oo-site: A dashboard to visualize gene expression during Drosophila oogenesis reveals meiotic entry is regulated post-transcriptionally

“…Our bulk RNA-seq data, as well as the available scRNA-seq data indicated that RpS19b was highly expressed in GSCs, decreased during differentiation in the cyst stages and was greatly decreased in expression in early egg chambers, consistent with previous reports (Fig (McCarthy et al, 2021;Sarkar et al, 2021). To further validate this expression pattern, we probed the expression of RpS19b in vivo using in situ hybridization as well as an RpS19b::GFP line that is under endogenous control elements (McCarthy et al, 2021). We found that RpS19b was present in the GSCs and diminishes in the cyst stages both at the mRNA and protein level (Figure 2C-E').…”

“…To determine if the bulk RNA-seq data recapitulates genuine changes in gene expression, we compared the expression of ribosomal small subunit protein 19b ( RpS19b ) in bulk RNA-seq to scRNA-seq data. Our bulk RNA-seq data, as well as the available scRNA-seq data indicated that RpS19b was highly expressed in GSCs, decreased during differentiation in the cyst stages and was greatly decreased in expression in early egg chambers, consistent with previous reports ( Fig 2A-B ) (McCarthy et al, 2021; Sarkar et al, 2021). To further validate this expression pattern, we probed the expression of RpS19b in vivo using in situ hybridization as well as an RpS19b::GFP line that is under endogenous control elements (McCarthy et al, 2021).…”

“…We were surprised to find no significant change in the mean mRNA expression of genes in this GO-term in any of our enriched stages compared to enriched GSCs, though this does not preclude gene expression changes for individual genes ( Supplemental Figure 3A ). However, this is consistent with the observation that several factors that promote meiosis I are transcribed in the GSCs and the cells that follow (McCarthy et al, 2021). This suggests that, in general, a transition from a mitotic state to a meiotic state is not driven by large changes in mRNA levels of meiotic genes.…”

“…The following RNAi stocks were used in this study; ord-GFP (Bickel Lab), Rps19b::GFP (McCarthy et al, 2021), UAS-Dcr2;nosGAL4 (Bloomington stock #25751), bam RNAi (Bloomington #58178), hs-bam /TM3 (Bloomington #24637),…”