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

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.

Targeted inhibition of WRN helicase by external guide sequence and RNase P RNA.

Human WRN, a RecQ helicase encoded by the Werner syndrome gene, is implicated in genome maintenance, including replication, recombination, excision repair and DNA damage response. These genetic processes and expression of WRN are concomitantly upregulated in many types of cancers. Therefore, targeted destruction of this helicase could be useful for elimination of cancer cells. Here, we provide a proof of concept for applying the external guide sequence (EGS) approach in directing an RNase P RNA to efficiently cleave the WRN mRNA in cultured human cell lines, thus abolishing translation and activity of this distinctive 3'-5' DNA helicase-nuclease. Remarkably, EGS-directed knockdown of WRN leads to severe inhibition of cell viability. Hence, further assessment of this targeting system could be beneficial for selective cancer therapies, particularly in the light of the recent improvements introduced into EGSs.