Maturation of the developing heart requires the structural elaboration of the embryonic ventricle through the process of trabeculation. Trabeculae form as the ventricular myocardium protrudes into the lumen of the chamber, thereby increasing muscle mass and altering functional output. Little is understood about the cellular basis for trabeculation and its genetic regulation. Here, we establish the utility of the zebrafish embryo for the analysis of the mechanisms driving trabeculation. In zebrafish, we can follow trabeculation in four dimensions and define morphologically discrete stages for the initiation, propagation, and network elaboration that form the ventricular trabeculae. We find that Neuregulin/ErbB signaling is required for the initial protrusion of the myocardium into the ventricular lumen. Additionally, we demonstrate that optimal blood flow through the ventricle is important for the advancement of trabeculation. Thus, our results indicate that the zebrafish provides a valuable model for investigating possible causes of congenital defects in trabeculation. Developmental Dynamics 240:446-456,

Branching morphogenesis is a central event during the development of kidneys, lungs, and other organs. We previously generated a monoclonal antibody, 3D2-E9, that inhibited branching morphogenesis and caused widespread apoptosis. We now report the purification of its antigen and cloning of its full-length cDNA. Its cDNA encodes an integral membrane protein that contains four cadherin-like ectodomains and a thrice tandemly repeated region enriched in threonine, serine, and proline, similar to those of mucins. We thus term this protein -protocadherin, reflecting the hybrid nature of its extracellular region. -Protocadherin is expressed in two forms that are developmentally regulated, with the shorter isoform lacking the mucin-like repeats. Expression of the long isoform in heterologous cells results in adhesion of the expressing cells, suggesting that it is a new cell adhesion molecule. -Protocadherin contains both N and O glycosylations. It is expressed at lateral and basal surfaces of epithelia during kidney and lung development and is located in coated pits. Colocalization of -protocadherin with ␤-catenin was noted primarily at the junction of the lateral and basal membrane. The cytoplasmic domain contains four prolinerich regions, similar to SH3 binding regions. Thus, it is likely that adhesive interactions mediated by -protocadherin induce signaling events that regulate branching morphogenesis.

COVER PHOTOGRAPH: Three‐dimensional reconstruction of the inner surface of the ventricular chamber of the zebrafish heart. The apparent ridges represent the initial stages of cardiac trabeculation, during which myocardial protrusions transform the previously smooth lumenal surface. From Peshkovsky et al., Developmental Dynamics 240:446‐456, 2011. © 2011 Wiley‐Liss, Inc.

Purulent pericarditis occurs rarely in the current antibiotic era. We describe clinical and echocardiographic features of purulent pericarditis in a previously healthy child with influenza and community-acquired methicillin-resistant Staphylococcus aureus co-infection. The child was already on appropriate antibiotics and had a very subtle clinical presentation, with prominent abdominal symptoms. Timely surgical drainage led to complete recovery.

The surgical correction of congenital cardiac lesions that are complicated by intercurrent respiratory syncytial virus (RSV) pneumonitis has traditionally been deferred for at least 6 to 8 weeks. The presumption is that using cardiopulmonary bypass will increase the risk of postoperative pulmonary complications. We present an infant who developed acute respiratory failure related to RSV pneumonitis and required urgent mechanical ventilation. Cardiac evaluation revealed a large nonrestrictive ventricular septal defect (VSD), aortic arch hypoplasia, normally functioning bicuspid aortic valve, and hemodynamic instability associated with markedly increased pulmonary blood flow. Separation from mechanical ventilation was unsuccessful preoperatively. He underwent VSD repair with cardiopulmonary bypass less than 4 weeks after initial RSV infection. He was extubated successfully within 72 hours of VSD repair. Approximately 6 weeks postoperatively, he developed a circumferential chylous pericardial effusion of unclear etiology--an exceedingly rare complication of VSD repair in early infancy in a non-Down syndrome patient. The chylous effusion was initially managed unsuccessfully with Portogen/Monogen and a percutaneously placed pericardial drain. Two weeks later, he underwent creation of a pleuropericardial window with successful resolution of the chylous effusion. It is of interest to pediatricians to be able to correctly time the repair of congenital heart disease lesions after RSV infection to minimize post-bypass pulmonary complications and yet avoid morbidity from undue delays in repair. In addition, chylopericardium can occur in infants after VSD repair, and dietary modification and catheter drainage may not be adequate.