Conducting the embryonic heart: Orchestrating development of specialized cardiac tissues

The heterogeneous tissues of the pacemaking and conduction system comprise the "smart components" of the heart, responsible for setting, maintaining, and coordinating the rhythmic pumping of cardiac muscle. Over the last few years, a wealth of new information has been collected about the unique gene tic and phenotypic characteristics expressed by these tissues during cardia c morphogenesis. More recently, genetically modified viruses, mutational an alysis, and targeted transgenesis have enabled evert move precise resolutio n of the relationships between cell fate, gene expression, and differentiat ion of specialized function within developing myocardium. While some inform ation. provided by these newer approaches has supported conventional wisdom , some fresh and unexpected perspectives have also emerged. In particular t here is mounting evidence that extracardiac populations of cells migrating into the tubular heart have important morphogenetic voles in the inductive patterning and functional integration of the developing conduction system. (C) 1999 Elsevier Science Inc.