RESUMEN
Enhancers exist in different epigenetic states: active, primed, or poised. However, it is not yet understood how the different enhancer states influence gene activation. In this issue of Cell Stem Cell, Cruz-Molina et al. (2017) unravel how poised enhancers activate anterior neural genes and the role of Polycomb proteins in enhancer-promoter contacts.
Asunto(s)
Elementos de Facilitación Genéticos/genética , Neuronas/metabolismo , Complejo Represivo Polycomb 2/metabolismo , Regiones Promotoras Genéticas/genética , Animales , Epigénesis Genética/genética , Humanos , Ratones , Modelos Teóricos , Complejo Represivo Polycomb 2/genéticaRESUMEN
Regulation of hematopoietic stem and progenitor cell (HSPC) steady-state egress from the bone marrow (BM) to the circulation is poorly understood. While glycogen synthase kinase-3ß (GSK3ß) is known to participate in HSPC proliferation, we revealed an unexpected role in the preferential regulation of CXCL12-induced migration and steady-state egress of murine HSPCs, including long-term repopulating HSCs, over mature leukocytes. HSPC egress, regulated by circadian rhythms of CXCL12 and CXCR4 levels, correlated with dynamic expression of GSK3ß in the BM. Nevertheless, GSK3ß signaling was CXCL12/CXCR4 independent, suggesting that synchronization of both pathways is required for HSPC motility. Chemotaxis of HSPCs expressing higher levels of GSK3ß compared with mature cells was selectively enhanced by stem cell factor-induced activation of GSK3ß. Moreover, HSPC motility was regulated by norepinephrine and insulin-like growth factor-1 (IGF-1), which increased or reduced, respectively, GSK3ß expression in BM HSPCs and their subsequent egress. Mechanistically, GSK3ß signaling promoted preferential HSPC migration by regulating actin rearrangement and microtubuli turnover, including CXCL12-induced actin polarization and polymerization. Our study identifies a previously unknown role for GSK3ß in physiological HSPC motility, dictating an active, rather than a passive, nature for homeostatic egress from the BM reservoir to the blood circulation.