Polycomb-mediated gene repression is essential for embryonic development, yet its precise role in lineage-specific programming is poorly understood. Here we inactivated Ring1b, encoding a polycomb-repressive complex 1 subunit, in pancreatic multipotent progenitors (Ring1b progKO ). This caused transcriptional derepression of a subset of direct Ring1b target genes in differentiated pancreatic islet cells. Unexpectedly, Ring1b inactivation in differentiated islet b cells (Ring1b bKO ) did not cause derepression, even after multiple rounds of cell division, suggesting a role for Ring1b in the establishment but not the maintenance of repression. Consistent with this notion, derepression in Ring1b progKO islets occurred preferentially in genes that were targeted de novo by Ring1b during pancreas development. The results support a model in which Ring1b bookmarks its target genes during embryonic development, and these genes are maintained in a repressed state through Ring1b-independent mechanisms in terminally differentiated cells. This work provides novel insights into how epigenetic mechanisms contribute to shaping the transcriptional identity of differentiated lineages. Throughout embryonic development, an interplay between positive and negative regulatory mechanisms promotes dynamic changes in chromatin structure that set up lineage-specific transcriptional programs. Although current knowledge supports this general model, the exact manner in which chromatin regulatory complexes contribute to differentiation programs remains to be defined.One of the key mechanisms to create repressive chromatin states is mediated by Polycomb group (PcG) proteins (Sparmann and van Lohuizen 2006;Schwartz and Pirrotta 2007;Schuettengruber and Cavalli 2009;Vidal 2009;Margueron and Reinberg 2011). PcG proteins form two major families of complexes, named Polycomb-repressive complex 1 (PRC1) and PRC2. PRC2 comprises Eed, Suz12, and two related subunits, Ezh1 and Ezh2, that catalyze the trimethylation of histone H3K27 (H3K27me3). PRC1 complexes include Bmi1, Cbx proteins, Mel18, and the ring finger proteins Ring1a and Ring1b (Vidal 2009). Among these, Ring1b has a primary role in catalyzing another post-translational histone modification, H2A K119 ubiquitination (de Napoles et al. 2004;Wang et al. 2004). Ring1b-mediated repression is linked to H2A ubiquitination, although Ring1b also promotes chromatin compaction independently of this histone-modifying activity (Eskeland et al. 2010). Thus, many of the molecular components and mechanisms underlying PcG-mediated repression have begun to be unraveled.Multiple lines of evidence indicate that PcG proteins are pivotal for embryonic developmental programs. Notably, several Drosophila and mouse PcG mutants have shown embryonic lethality or homeotic transformations due to derepression of Hox genes (e.g., Lewis 1978;O'Carroll et al. 2001;Voncken et al. 2003
BackgroundStudies on osteoclasts, the bone resorbing cells, have remained limited due to the lack of transgenic mice allowing the conditional knockout of genes in osteoclasts at any time during development or adulthood.Methodology/Principal FindingWe report here on the generation of transgenic mice which specifically express a tamoxifen-inducible Cre recombinase in osteoclasts. These mice, generated on C57BL/6 and FVB background, express a fusion Cre recombinase-ERT2 protein whose expression is driven by the promoter of cathepsin K (CtsK), a gene highly expressed in osteoclasts. We tested the cellular specificity of Cre activity in CtsKCreERT2 strains by breeding with Rosa26LacZ reporter mice. PCR and histological analyses of the CtsKCreERT2LacZ positive adult mice and E17.5 embryos show that Cre activity is restricted largely to bone tissue. In vitro, primary osteoclasts derived from the bone marrow of CtsKCreERT2+/−LacZ+/− adult mice show a Cre-dependent β-galactosidase activity after tamoxifen stimulation.Conclusions/SignificanceWe have generated transgenic lines that enable the tamoxifen-induced, conditional deletion of loxP-flanked genes in osteoclasts, thus circumventing embryonic and postnatal gene lethality and avoiding gene deletion in other cell types. Such CtsKCreERT2 mice provide a convenient tool to study in vivo the different facets of osteoclast function in bone physiology during different developmental stages and adulthood of mice.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.