Combgap Promotes Ovarian Niche Development and Chromatin Association of EcR-Binding Regions in BR-C

Abstract

The development of niches for tissue-specific stem cells is an important aspect of stem cell biology. Determination of niche size and niche numbers during organogenesis involves precise control of gene expression. How this is achieved in the context of a complex chromatin landscape is largely unknown. Here we show that the nuclear protein Combgap (Cg) supports correct ovarian niche formation in Drosophila by controlling ecdysone-Receptor (EcR)- mediated transcription and long-range chromatin contacts in the broad locus (BR-C). Both cg and BR-C promote ovarian growth and the development of niches for germ line stem cells. BR-C levels were lower when Combgap was either reduced or over-expressed, indicating an intricate regulation of the BR-C locus by Combgap. Polytene chromosome stains showed that Cg co-localizes with EcR, the major regulator of BR-C, at the BR-C locus and that EcR binding to chromatin was sensitive to changes in Cg levels. Proximity ligation assay indicated that the two proteins could reside in the same complex. Finally, chromatin conformation analysis revealed that EcR-bound regions within BR-C, which span ~30 KBs, contacted each other. Significantly, these contacts were stabilized in an ecdysone- and Combgap-dependent manner. Together, these results highlight Combgap as a novel regulator of chromatin structure that promotes transcription of ecdysone target genes and ovarian niche formation.

Identification of regulators of germ stem cell enwrapment by its niche in C. elegans

“…One gene that is necessary for DTC elaboration is lin-40 /MTA1, a chromatin regulator, which is part of the nucleosome remodeling and histone deacetylation (NuRD) complex (Solari et al, 1999). Formation of other stem cell niches, including in the murine testis (Wu et al, 2017) and in the Drosophila ovary (Hitrik et al, 2016; Upadhyay et al, 2016), also requires specific chromatin regulators. As the DTC actively remodels from a simple cap to a highly branched and elaborate structure, energetically intensive and dynamic membrane addition and remodeling may also be key components underlying plexus formation.…”

Antagonistic regulation of the second mitotic wave by Eyes absent-Sine oculis and Combgap coordinates proliferation and specification in the Drosophila retina

“…S3), its contributions to retinal development have not been described. Mechanistically, Cg works as a sequence-specific DNA-binding protein that contributes to recruitment of Polycomb repressive complexes (Ray et al, 2016), can organize the three-dimensional conformation of target loci (Hitrik et al, 2016), and is thought to activate and repress targets in the leg, wing and brain (Campbell and Tomlinson, 2000;Song et al, 2000;Svendsen et al, 2000). Based on this prior knowledge, Cg presented an intriguing candidate for a transcription factor that might influence the output of Eya-So.…”

A direct and widespread role for the nuclear receptor EcR in mediating the response to ecdysone inDrosophila

“…Given the hierarchical structure of the ecdysone pathway, it is unclear if EcR acts primarily at the top of the transcriptional cascade, or if it also acts directly on downstream effector genes. Several early response genes such as br, Eip74EF, and the glue genes have been shown to be directly bound by EcR in vivo (5, 21, 22). At the genome-wide level, polytene chromosome staining revealed approximately 100 sites bound by EcR in larval salivary glands (23).…”