Summary The vascular system is essential for embryonic development and adult life. Aberrant vascularization is associated with numerous diseases, including cancer, atherosclerosis, retinopathy, and stroke. Vascular development begins when mesodermal cells differentiate into endothelial cells, which then form primitive vessels. It has been hypothesized that endothelial-specific gene expression may be regulated combinatorially, but the transcriptional mechanisms governing vascular gene expression remain incompletely understood. Here, we identify a transcriptional code, consisting of Forkhead and Ets factors, which is required and sufficient for vascular development and endothelial gene expression through combinatorial activation of a composite cis-acting element. We show that the presence of this FOX:ETS motif is an effective predictor of endothelial-specific enhancers. These studies establish a paradigm in which two broadly expressed classes of transcription factors regulate tissue specific expression combinatorially through a single composite cis-acting element. This mechanism has broad implications for understanding differentiation and gene expression in many tissues.

Background-Cardiac hypertrophy is a common response to pressure overload and is associated with increased mortality.Mechanical stress in the heart results in the activation of the small GTPase ras and the Raf-1/MEK/ERK signaling cascade in addition to other signaling pathways. Methods and Results-In an attempt to determine the requirement for the serine/threonine kinase Raf-1 in the pathogenesis of cardiac hypertrophy, we generated transgenic mice with cardiac-specific expression of a dominant negative form of Raf-1 (DN-Raf). DN-Raf mice appeared normal at birth, were fertile, and had normal cardiac structure and function in the absence of provocative stimulation. In response to pressure overload, cardiac extracellular signal-regulated kinase (ERK) activation was inhibited, but c-Jun N-terminal kinase (JNK) activation and p38 mitogen-activated protein kinase (MAPK) activation were normal. DN-Raf mice were sensitized to pressure overload and the development of cardiomyocyte apoptosis, and Ͼ35% of animals died within 7 days of aortic banding. Surviving DN-Raf animals were markedly resistant to the development of cardiac hypertrophy and hypertrophic gene induction in response to transverse aortic constriction. Conclusions-These results establish that Raf-1 kinase activity is essential for cardiac hypertrophy and cardiomyocyte survival in response to pressure overload.

The endocardium, the endothelial lining of the heart, plays complex and critical roles in heart development, particularly in the formation of the cardiac valves and septa, the division of the truncus arteriosus into the aortic and pulmonary trunks, the development of Purkinje fibers that form the cardiac conduction system, and the formation of trabecular myocardium. Current data suggest that the endocardium is a regionally specialized endothelium that arises through a process of de novo vasculogenesis from a distinct population of mesodermal cardiogenic precursors in the cardiac crescent. In this article, we review recent developments in the understanding of the embryonic origins of the endocardium. Specifically, we summarize vasculogenesis and specification of endothelial cells from mesodermal precursors, and we review the transcriptional pathways involved in these processes. We discuss the lineage relationships between the endocardium and other endothelial populations and between the endocardium and the myocardium. Finally, we explore unresolved questions about the lineage relationships between the endocardium and the myocardium. One of the central questions involves the timing with which mesodermal cells, which arise in the primitive streak and migrate to the cardiac crescent, become committed to an endocardial fate. Two competing conceptual models of endocardial specification have been proposed. In the first, mesodermal precursor cells in the cardiac crescent are prespecified to become either endocardial or myocardial cells, while in the second, fate plasticity is retained by bipotential cardiogenic cells in the cardiac crescent. We propose a third model that reconciles these two views and suggest future experiments that might resolve this question.

Congenital heart diseases are the most common birth defects in humans, affecting approximately 0.8% of all live births. In the past, many of the more severe defects resulted in profound disability and death during childhood, and adult survival was exceptional. The past 4 decades have seen dramatic improvements in the survival and quality of life of patients with the more severe defects. As a result of these improvements, the challenges of caring for adults with congenital heart disease are only now being realized. The majority of women with congenital heart disease are now expected to reach childbearing age and maternal cardiac disease is the major cause of maternal morbidity and mortality. As such, appropriate pre-pregnancy counseling and management during pregnancy are fundamental components of the care of these patients. This article describes the circulatory changes that occur during normal pregnancy and delivery, addresses the risks posed during pregnancy by specific congenital lesions, and reviews the current data on pregnancy outcomes in patients with individual congenital defects.

The MyoD family of basic helix-loop-helix (bHLH) transcription factors has the remarkable ability to induce myogenesis in vitro and in vivo. This myogenic specificity has been mapped to two amino acids in the basic domain, an alanine and threonine, referred to as the myogenic code. These essential determinants of myogenic specificity are conserved in all MyoD family members from worms to humans, yet their function in myogenesis is unclear. Induction of the muscle transcriptional program requires that MyoD be able to locate and stably bind to sequences present in the promoter regions of critical muscle genes. Recent studies have shown that MyoD binds to noncanonical E boxes in the myogenin gene, a critical locus required for myogenesis, through interactions with resident heterodimers of the HOX-TALE transcription factors Pbx1A and Meis1. In the present study, we show that the myogenic code is required for MyoD to bind to noncanonical E boxes in the myogenin promoter and for the formation of a tetrameric complex with Pbx/Meis. We also show that these essential determinants of myogenesis are sufficient to confer noncanonical E box binding to the E12 basic domain. Thus, these data show that noncanonical E box binding correlates with myogenic potential, and we speculate that the myogenic code residues in MyoD function as myogenic determinants via their role in noncanonical E box binding and recognition.