Drosophila small ovary gene is required for transposon silencing and heterochromatin organization, and ensures germline stem cell maintenance and differentiation

Abstract

Self-renewal and differentiation of stem cells is one of the fundamental biological phenomena relying on proper chromatin organization. In our study, we describe a novel chromatin regulator encoded by the Drosophila small ovary (sov) gene. We demonstrate that sov is required in both the germline stem cells (GSCs) and the surrounding somatic niche cells to ensure GSC survival and differentiation. sov maintains niche integrity and function by repressing transposon mobility, not only in the germline, but also in the soma. Protein interactome analysis of Sov revealed an interaction between Sov and HP1a. In the germ cell nuclei, Sov colocalizes with HP1a, suggesting that Sov affects transposon repression as a component of the heterochromatin. In a position-effect variegation assay, we found a dominant genetic interaction between sov and HP1a, indicating their functional cooperation in promoting the spread of heterochromatin. An in vivo tethering assay and FRAP analysis revealed that Sov enhances heterochromatin formation by supporting the recruitment of HP1a to the chromatin. We propose a model in which sov maintains GSC niche integrity by regulating transposon silencing and heterochromatin formation.

DrosophilaHeterochromatin Stabilization Requires the Zinc-Finger Protein Small Ovary

“…The sov germline phenotype in the clonal analysis was also more extreme than the germline RNAi phenotype, suggesting that our RNAi experiments only partially reduced sov expression. Taken together, our data support a role for Sov in both the germline and the soma, consistent with recent reports (Jankovics et al 2018).…”

Quantitative analysis of subcellular distributions with an open-source, object-based tool

“…Sov facilitates heterochromatin stabilization and is required for embryonic viability ( Benner et al, 2019 ; Jankovics et al, 2018 ). Although Sov protein resides within the nucleus ( Benner et al, 2019 ), sov mRNA localizes near centrosomes ( Lécuyer et al, 2007 ; Ryder et al, 2020 preprint).…”

The SUMO Ligase Su(var)2-10 Controls Hetero- and Euchromatic Gene Expression via Establishing H3K9 Trimethylation and Negative Feedback Regulation

“…Su(var)2-10 also represses expression of two recently identified proteins that interact with the protein HP1, which is critical for heterochromatin packaging: Sov and CG30403. Sov is a suppressor of positional effect variegation and plays a role in recruitment of HP1 to chromatin (Alekseyenko et al, 2014;Jankovics et al, 2018). To further investigate the role of Sov in heterochromatin formation, we tested the effect of sov GLKD on the genome-wide distribution of the H3K9me3 mark in the ovary using ChIP-seq.…”

“…Furthermore, HP1 is a hub that interacts with many other heterochromatin proteins (Eissenberg and Elgin, 2014). Both Sov and CG30403 interact with HP1, and Sov is critical for heterochromatin maintenance (Jankovics et al, 2018 , Fig. S1).…”

“…For UASp-shSmt3, the anti-Smt3 shRNA sequence based on the TRiP line HMS01540 ( Supplementary Table S1) was ligated into the pValium20 vector (Ni et al 2011) using T4 DNA ligase from NEB, according to the manufacturer's instructions and was integrated at the attP2 landing site by BestGene. UASp-shSetDB1 stocks were a gift from Julius Brennecke, and UASp-shSov stocks were obtained from Miklos Erdelyi (Jankovics et al, 2018). The expression of all constructs was driven by maternal alpha-tubulin67C-Gal4 (MT-Gal4, BDSC #7063), except for the shSUMO H3K9me3 ChIP-seq samples, where the BDSC #7062 stock encoding alpha-tubulin67C-Gal4 driver was used.…”