Enhanced fetal γ-globin synthesis alleviates symptoms of β-globinopathies such as sickle cell disease and β-thalassemia, but current γ-globin–inducing drugs offer limited beneficial effects. We show here that lysine-specific demethylase 1 (LSD1) inhibition by RNAi in human erythroid cells or by the monoamine oxidase inhibitor tranylcypromine in human erythroid cells or β-type globin–transgenic mice enhances γ-globin expression. LSD1 is thus a promising therapeutic target for γ-globin induction, and tranylcypromine may serve as a lead compound for the development of a new γ-globin inducer.

SummaryThe gap in knowledge of the molecular mechanisms underlying differentiation of human pluripotent stem cells (hPSCs) into the mesenchymal cell lineages hinders the application of hPSCs for cell-based therapy. In this study, we identified a critical role of muscle segment homeobox 2 (MSX2) in initiating and accelerating the molecular program that leads to mesenchymal stem/stromal cell (MSC) differentiation from hPSCs. Genetic deletion of MSX2 impairs hPSC differentiation into MSCs. When aided with a cocktail of soluble molecules, MSX2 ectopic expression induces hPSCs to form nearly homogeneous and fully functional MSCs. Mechanistically, MSX2 induces hPSCs to form neural crest cells, an intermediate cell stage preceding MSCs, and further differentiation by regulating TWIST1 and PRAME. Furthermore, we found that MSX2 is also required for hPSC differentiation into MSCs through mesendoderm and trophoblast. Our findings provide novel mechanistic insights into lineage specification of hPSCs to MSCs and effective strategies for applications of stem cells for regenerative medicine.

Nuclear receptors TR2 and TR4 (TR2/TR4) were previously shown to bind in vitro to direct repeat elements in the mouse and human embryonic and fetal ␤-type globin gene promoters and to play critical roles in the silencing of these genes. By chromatin immunoprecipitation (ChIP) we show that, in adult erythroid cells, TR2/TR4 bind to the embryonic ␤-type globin promoters but not to the adult ␤-globin promoter. We purified protein complexes containing biotin-tagged TR2/TR4 from adult erythroid cells and identified DNMT1, NuRD, and LSD1/CoREST repressor complexes, as well as HDAC3 and TIF1␤, all known to confer epigenetic gene silencing, as potential corepressors of TR2/TR4. Coimmunoprecipitation assays of endogenous abundance proteins indicated that TR2/TR4 complexes consist of at least four distinct molecular species. In ChIP assays we found that, in undifferentiated murine adult erythroid cells, many of these corepressors associate with both the embryonic and the adult ␤-type globin promoters but, upon terminal differentiation, they specifically dissociate only from the adult ␤-globin promoter concomitant with its activation but remain bound to the silenced embryonic globin gene promoters. These data suggest that TR2/TR4 recruit an array of transcriptional corepressors to elicit adult stage-specific silencing of the embryonic ␤-type globin genes through coordinated epigenetic chromatin modifications.Regulatory pathways that control development through temporally specified gene activation and repression mechanisms have been recognized as "epigenetic" (i.e., heritable changes not involving alterations in the primary DNA code) for decades, although the molecules that elicit those developmental programs through epigenetic means have only been elucidated during the past several years. It is currently widely accepted that metazoan transcription factors (both activators and repressors) elicit their specific transcriptional responses through an enormous variety of cofactor molecules whose major purpose is to modulate chromatin structure (8, 31). Many such cofactors have been shown to chemically modify histones, transcription factors, and cofactors, as well as DNA, in order to elicit the required transcriptional responses.The ␤-globin locus has been extensively studied as a paradigm for epigenetic regulation of lineage-specific and developmentally specific gene expression (29), as well as for its clinical relevance to ␤-globin disorders such as sickle cell disease and ␤-thalassemia. The human ␤-globin locus is composed of ε-(embryonic), G␥-and A␥-(fetal), and ␦-and ␤-globin (adult) genes, which are spatially arranged from 5Ј to 3Ј and developmentally expressed in the same order (72). The elucidation of the molecular basis for ␥-globin silencing in the adult stage in particular has been the focus of intense investigation, since it has been observed that coinheritance of genetic conditions that confer elevated ␥-globin synthesis can significantly alleviate the symptoms of ␤-globin disorders (44, 56). Previously, several adul...

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