PT - JOURNAL ARTICLE AU - Ferenc Jankovics AU - Melinda Bence AU - Rita Sinka AU - Anikó Faragó AU - László Bodai AU - Aladár Pettkó-Szandtner AU - Karam Ibrahim AU - Zsanett Takács AU - Alexandra Brigitta Szarka-Kovács AU - Miklós Erdélyi TI - Drosophila <em>small ovary</em> gene ensures germline stem cell maintenance and differentiation by silencing transposons and organising heterochromatin AID - 10.1101/383265 DP - 2018 Jan 01 TA - bioRxiv PG - 383265 4099 - http://biorxiv.org/content/early/2018/08/02/383265.short 4100 - http://biorxiv.org/content/early/2018/08/02/383265.full AB - Self-renewal and differentiation of stem cells is one of the fundamental biological phenomena relying on proper chromatin organisation. 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 a physical interaction between Sov and HP1a. In the germ cell nuclei, Sov co-localises 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 piRNA-mediated transposon silencing as a heterochromatin regulator.Summary statement Small ovary maintains the integrity of the stem cell niche by regulating piRNA-mediated transposon silencing acting as a key component of the heterochromatin.