Intersecting signalling and transcriptional pathways in Drosophila heart specification.

The Drosophila heart, also called the dorsal vessel, is a linear tube consisting of two major cell types, namely cardioblasts which serve as cardiomyocytes and pericardial cells which surround its outer surface. This organ is derived from segmental clusters of cells in the dorsal mesoderm during early embryonic development. During the past few years, genetic and molecular studies have led to significant advances in our understanding of the regulatory mechanisms that pattern the early mesoderm by defining these cell clusters and ultimately specifying individual cells within them as heart progenitors. These studies established that the patterning events involve specific combinations of localized inductive signals that act in concert with mesoderm-autonomous transcription factors to achieve a progressive subdivision of the mesoderm. Some of the synergistic interactions between mesodermal transcription factors and external signalling molecules have been defined at the molecular level. With respect to the pericardial cells, the final specification steps were found to employ cell-intrinsic lineage mechanisms. Because of the many striking similarities between Drosophila and early vertebrate heart development, which appear to extend to the molecular level, these insights will be of significant help in defining related events during vertebrate cardiogenesis.