Understanding the origins and roles of cardiac progenitor cells is important for elucidating the pathogenesis of congenital and acquired heart diseases. Moreover, manipulation of cardiac myocyte progenitors has potential for cell-based repair strategies for various myocardial disorders. Here we report the identification in mouse of a previously unknown cardiac myocyte lineage that derives from the proepicardial organ. These progenitor cells, which express the T-box transcription factor Tbx18, migrate onto the outer cardiac surface to form the epicardium, and then make a substantial contribution to myocytes in the ventricular septum and the atrial and ventricular walls. Tbx18-expressing cardiac progenitors also give rise to cardiac fibroblasts and coronary smooth muscle cells. The pluripotency of Tbx18 proepicardial cells provides a theoretical framework for applying these progenitors to effect cardiac repair and regeneration.

Recent studies have demonstrated that the LIM homeodomain transcription factor Islet1 (Isl1) marks pluripotent cardiovascular progenitor cells and is required for proliferation, survival, and migration of recently defined second heart field progenitors. Factors that are upstream of Isl1 in cardiovascular progenitors have not yet been defined. Here we demonstrate that ␤-catenin is required for Isl1 expression in cardiac progenitors, directly regulating the Isl1 promoter. Ablation of ␤-catenin in Isl1-expressing progenitors disrupts multiple aspects of cardiogenesis, resulting in embryonic lethality at E13. ␤-Catenin is also required upstream of a number of genes required for pharyngeal arch, outflow tract, and/or atrial septal morphogenesis, including Tbx2, Tbx3, Wnt11, Shh, and Pitx2. Our findings demonstrate that ␤-catenin signaling regulates proliferation and survival of cardiac progenitors.cardiac morphogenesis ͉ cardiac progenitors ͉ direct target ͉ Isl1

The giant protein obscurin is thought to link the sarcomere with the sarcoplasmic reticulum (SR). The N-terminus of obscurin interacts with the M-band proteins titin and myomesin, whereas the C-terminus mediates interactions with ankyrin proteins. Here, we investigate the importance of obscurin for SR architecture and organization. Lack of obscurin in crossstriated muscles leads to changes in longitudinal SR architecture and disruption of small ankyrin-1.5 (sAnk1.5) expression and localization. Changes in SR architecture in obscurin knockout mice are also associated with alterations in several SR or SRassociated proteins, such as ankyrin-2 and β-spectrin. Finally, obscurin knockout mice display centralized nuclei in skeletal muscles as a sign of mild myopathy, but have normal sarcomeric structure and preserved muscle function. Supplementary material available online at

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Traumatic brain injury (TBI) is a leading cause of sustained impairment in military and civilian populations. However, mild (and some moderate) TBI can be difficult to diagnose due to lack of obvious external injuries and because the injuries are often not visible on conventional acute MRI or CT. Injured brain tissues in TBI patients generate pathological low-frequency neuronal magnetic signal (delta waves 1-4 Hz) that can be measured and localized by magnetoencephalography (MEG). We hypothesize that abnormal MEG delta waves originate from gray matter neurons that experience de-afferentation due to axonal injury to the underlying white matter fiber tracts, which is manifested on diffusion tensor imaging (DTI) as reduced fractional anisotropy. The present study used a neuroimaging approach integrating findings of magnetoencephalography (MEG) and diffusion tensor imaging (DTI), evaluating their utility in diagnosing mild TBI in 10 subjects in whom conventional CT and MRI showed no visible lesions in 9. The results show: (1) the integrated approach with MEG and DTI is more sensitive than conventional CT and MRI in detecting subtle neuronal injury in mild TBI; (2) MEG slow waves in mild TBI patients originate from cortical gray matter areas that experience de-afferentation due to axonal injuries in the white matter fibers with reduced fractional anisotropy; (3) findings from the integrated imaging approach are consistent with post-concussive symptoms; (4) in some cases, abnormal MEG delta waves were observed in subjects without obvious DTI abnormality, indicating that MEG may be more sensitive than DTI in diagnosing mild TBI.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) termed a 'disease of the desmosome' is an inherited cardiomyopathy that recently underwent reclassification owing to the identification of left-dominant and biventricular disease forms. Homozygous loss-of-function mutations in the desmosomal component, desmoplakin, are found in patients exhibiting a biventricular form of ARVC; however, no models recapitulate the postnatal hallmarks of the disease as seen in these patients. To gain insights into the homozygous loss-of-function effects of desmoplakin in the heart, we generated cardiomyocyte-specific desmoplakin-deficient mice (DSP-cKO) using ventricular myosin light chain-2-Cre mice. Homozygous DSP-cKO mice are viable but display early ultrastructural defects in desmosomal integrity leading to a cardiomyopathy reminiscent of a biventricular form of ARVC, which includes cell death and fibro-fatty replacement within the ventricle leading to biventricular dysfunction, failure and premature death. DSP-cKO mice also exhibited ventricular arrhythmias that are exacerbated with exercise and catecholamine stimulation. Furthermore, DSP-cKO hearts exhibited right ventricular conduction defects associated with loss of connexin 40 expression and electrical wavefront propagation defects associated with loss of connexin 43 expression. Dose-dependent assessment of the effects of loss of desmoplakin in neonatal ventricular cardiomyocytes revealed primary loss of connexin 43 levels, phosphorylation and function independent of the molecular dissociation of the mechanical junction complex and fibro-fatty manifestation associated with ARVC, suggesting a role for desmoplakin as a primary stabilizer of connexin integrity. In summary, we provide evidence for a novel mouse model, which is reminiscent of the postnatal onset of ARVC while highlighting mechanisms underlying a biventricular form of human ARVC.

Rationale The Z-line, alternatively termed the Z-band or Z-disc, is a highly ordered structure at the border between two sarcomeres. Enigma subfamily proteins (Enigma, Enigma homolog protein and Cypher) of the PDZ-LIM domain protein family are Z-line proteins. Among the Enigma subfamily, Cypher has been demonstrated to play a pivotal role in the structure and function of striated muscle, whereas the role of Enigma homolog protein (ENH) in muscle remains largely unknown. Objective We studied the role of Enigma homolog protein in the heart using global and cardiac-specific ENH knockout mouse models. Methods and Results We identified new exons and splice isoforms for ENH in the mouse heart. Impaired cardiac contraction and dilated cardiomyopathy were observed in ENH null mice. Mice with cardiac specific ENH deletion developed a similar dilated cardiomyopathy. Like Cypher, ENH interacted with Calsarcin-1, another Z-line protein. Moreover, biochemical studies showed that ENH, Cypher short isoform and Calsarcin-1 are within the same protein complex at the Z-line. Cypher short isoform and Calsarcin-1 proteins are specifically downregulated in ENH null hearts. Conclusions We have identified an ENH-CypherS-Calsarcin protein complex at the Z-line. Ablation of ENH leads to destabilization of this protein complex and dilated cardiomyopathy.

SUMMARYThe placenta is a transient organ that is necessary for proper fetal development. Its main functional component is the trophoblast, which is derived from extra-embryonic ectoderm. Little is known about early trophoblast differentiation in the human embryo, owing to lack of a proper in vitro model system. Human embryonic stem cells (hESCs) differentiate into functional trophoblast following BMP4 treatment in the presence of feeder-conditioned media; however, this model has not been widely accepted, in part owing to a lack of proof for a trophoblast progenitor population. We have previously shown that p63, a member of the p53 family of nuclear proteins, is expressed in proliferative cytotrophoblast (CTB), precursors to terminally differentiated syncytiotrophoblast (STB) in chorionic villi and extravillous trophoblast (EVT) at the implantation site. Here, we show that BMP4-treated hESCs differentiate into bona fide CTB by direct comparison with primary human placental tissues and isolated CTB through gene expression profiling. We show that, in primary CTB, p63 levels are reduced as cells differentiate into STB, and that forced expression of p63 maintains cyclin B1 and inhibits STB differentiation. We also establish that, similar to in vivo events, hESC differentiation into trophoblast is characterized by a p63 + /KRT7 + CTB stem cell state, followed by formation of functional KLF4 + STB and HLA-G + EVT. Finally, we illustrate that downregulation of p63 by shRNA inhibits differentiation of hESCs into functional trophoblast. Taken together, our results establish that BMP4-treated hESCs are an excellent model of human trophoblast differentiation, closely mimicking the in vivo progression from p63 + CTB stem cells to terminally differentiated trophoblast subtypes.