Duchenne muscular dystrophy is a progressive and incurable neuromuscular disease caused by genetic and biochemical defects of the dystrophin-glycoprotein complex. Here we show the regenerative potential of myogenic progenitors derived from corrected dystrophic induced pluripotent stem (iPS) cells generated from fibroblasts of mice lacking both dystrophin and utrophin. We correct the phenotype of dystrophic iPS cells using a Sleeping Beauty transposon carrying the micro-utrophin (μUTRN) gene, differentiate these cells into skeletal muscle progenitors, and transplant them back into dystrophic mice. Engrafted muscles displayed large numbers of micro-utrophin-positive myofibers, with biochemically restored dystrophin-glycoprotein complex and improved contractile strength. The transplanted cells seed the satellite cell compartment, responded properly to injury and exhibit neuromuscular synapses. We also detect muscle engraftment after systemic delivery of these corrected progenitors. These results represent an important advance toward the future treatment of muscular dystrophies using genetically corrected autologous iPS cells.

Much remains unknown about the signals that induce early mesoderm to initiate hematopoietic differentiation. Here, we show that endoglin (Eng), a receptor for the TGF␤ superfamily, identifies all cells with hematopoietic fate in the early embryo. These arise in an Eng ؉ Flk1 ؉ mesodermal precursor population at embryonic day 7.5 (E7.5), a cell fraction also endowed with endothelial potential. In Eng-knockout embryos, hematopoietic colony activity and numbers of CD71 ؉ Ter119 ؉ erythroid progenitors were severely reduced. This coincided with severely reduced expression of embryonic globin and key bone morphogenic protein (BMP) target genes, including the hematopoietic regulators Scl, Gata1, Gata2, and Msx-1. To interrogate molecular pathways active in the earliest hematopoietic progenitors, we applied transcriptional profiling to sorted cells from E7. IntroductionDuring mouse development, hematopoiesis occurs at temporally and spatially distinct anatomic sites with the first appearance of hematopoietic cells observed in the blood island (BI) of the extraembryonic yolk sac (YS) at embryonic day 7 (E7.0). 1 This first wave of primitive hematopoiesis produces primitive erythrocytes, megakaryocytes, 2 and macrophages, and is followed by the generation of definitive hematopoietic precursors in the YS at approximately E8.25 days post coitum (dpc). 1 The emergence of hematopoietic stem cells (HSCs) capable of repopulating adult mice is first observed at E10.5 in the aorta-gonad-mesonephros (AGM) region, and later on in other hematopoietic sites, such as YS, placenta, and fetal liver. [3][4][5] HSCs have been proposed to originate from a common precursor for the hematopoietic and endothelial lineages, the hemangioblast, which was initially described using the in vitro embryonic stem cell (ESC) differentiation system, 6 and was later confirmed in the mouse 7 and zebrafish 8 systems. In the murine embryo, this precursor has been identified to be enriched in the primitive streak (PS), and expresses fetal liver kinase 1 (Flk-1 or VEGFR2) in addition to brachyury. Subsequently, these cells migrate to the extraembryonic region, where they give rise to hematopoietic and endothelial cells of the BIs. 7 Endothelial versus hematopoietic fate is thought to be specified en route to the extraembryonic destination because individual BIs are often polyclonal. 9 To date, little is known regarding the molecular and cellular mechanisms involved in the origin and early development of the hematopoietic lineage. It has been reported that signals from extraembryonic ectoderm and visceral endoderm, including fibroblast growth factor 8 (FGF8), WNT3, and hedgehog, are crucial for proper mesoderm patterning, and the latter two are also involved in the specification of the hematopoietic program. 10,11 Members of the TGF␤ superfamily have been shown to play an essential role during vascular development and hematopoiesis. Ligands for the TGF␤ family act through a receptor complex present in the cell surface, which upon phosphorylation causes the ac...