Cover image

Cover In the primitive chordate, Ciona intestinalis, fibroblast growth factor (FGF) signaling causes a subset of potential heart cells to migrate and differentiate. Shown here are confocal images of transgenic Ciona embryos in which descendents of precardiac founder cells express a fluorescent reporter gene (red), the tail muscle cells autonomously fluoresce (green), and the cell membranes have been stained with phalloidin (blue). In the control embryo (top image), the rostral daughters of the founder lineage are undergoing cardiogenesis, including migration away from their caudal sisters. In the lower embryo, targeted disruption of transcriptional activity downstream from FGF has blocked heart cell specification, so that all of the precardiac lineage cells remain in the tail. Such embryos will form heartless juveniles. (For details, see Davidson et al., p. 2728.)