Project description:To characterize the genetic basis of hybrid male sterility in detail, we used a systems genetics approach, integrating mapping of gene expression traits with sterility phenotypes and QTL. We measured genome-wide testis expression in 305 male F2s from a cross between wild-derived inbred strains of M. musculus musculus and M. m. domesticus. We identified several thousand cis- and trans-acting QTL contributing to expression variation (eQTL). Many trans eQTL cluster into eleven ‘hotspots,’ seven of which co-localize with QTL for sterility phenotypes identified in the cross. The number and clustering of trans eQTL - but not cis eQTL - were substantially lower when mapping was restricted to a ‘fertile’ subset of mice, providing evidence that trans eQTL hotspots are related to sterility. Functional annotation of transcripts with eQTL provides insights into the biological processes disrupted by sterility loci and guides prioritization of candidate genes. Using a conditional mapping approach, we identified eQTL dependent on interactions between loci, revealing a complex system of epistasis. Our results illuminate established patterns, including the role of the X chromosome in hybrid sterility.
Project description:Polycomb Repressive Complex 2 (PRC2) trimethylates lysine 27 of histone 3 (H3K27me3). This modification transcriptionally represses chromatin and its dynamics are essential for embryonic development. PRC2 also methylates its cofactor JARID2 and both methylated H3 tail and JARID2 allosterically activate the complex. PRC2 undergoes auto-methylation of its catalytic subunit, which stimulates its activity by an unknown mechanism. We show that automethylated PRC2 forms a dimer on substrate chromatin that results in autoactivation in trans. An inactive PRC2 protomer distal to the substrate nucleosome serves as an allosteric activator of the second PRC2 protomer, which is poised to methylate H3. Functional assays support our model of allosteric activation via dimerization, suggesting a novel mechanism of PRC2 trans-autoactivation that may be important for installation of H3K27me3 into naïve chromatin.
Project description:We identified genes expressed in mouse liver that are regulated by Cux2, a highly female-specific liver transcription factor whose expression is regulated by sex-dependent plasma GH patterns. Using adenovirus to overexpress Cux2 (Adeno-Cux2) in male liver, we show that Cux2 represses ~35% of male-biased genes and induces/de-represses ~35% of female-biased genes. Adeno-CMV was used as a control for adenoviral infection. (Published in: TL Conforto et al 2012, Mol Cell Biol. 2012, 32:4611-4627. PubMed PMID: 22966202; PMCID: PMC3486175)
Project description:The Wnt/b-catenin signaling inhibits adipogenesis. Genome-wide profiling studies have revealed the enrichment of histone H3K27 methyltransferase PRC2 on Wnt genes. However, the functional significance of such a direct link between the two types of developmental regulators in mammalian cells, and the role of PRC2 in adipogenesis, remain unclear. Here we show PRC2 and its H3K27 methyltransferase activity are required for adipogenesis. PRC2 directly represses Wnt1, 6, 10a and 10b genes in preadipocytes and during adipogenesis. Deletion of the enzymatic Ezh2 subunit of PRC2 eliminates H3K27me3 on Wnt promoters and de-represses Wnt expression, which leads to activation of Wnt/b-catenin signaling and inhibition of adipogenesis. Ectopic expression of the wild type Ezh2, but not the enzymatically inactive F667I mutant, prevents the loss of H3K27me3 and the defects in adipogenesis in Ezh2-/- preadipocytes. The adipogenesis defects in Ezh2-/- cells can be rescued by expression of adipogenic transcription factors PPARa, C/EBPb, or inhibitors of Wnt/b-catenin signaling. Interestingly, Ezh2-/- cells show marked increase of H3K27 acetylation globally as well as on Wnt promoters. These results indicate that H3K27 methyltransferase PRC2 directly represses Wnt genes to facilitate adipogenesis, and suggest that acetylation and trimethylation on H3K27 play opposing roles in regulating Wnt expression. To identify additional PRC2-regulated genes in preadipocytes, we performed microarray analysis in Ezh2flox/flox preadipocytes infected with retroviruses expressing Cre or vector alone.