Seeking a regulatory roadmap for heart morphogenesis.

Despite descriptive studies spanning centuries, we are still lacking an integrated concept of how molecular patterning information is developed in the heart, and how this information guides morphogenesis. With an increasing number of regionally-expressed cardiac genes and transgenes being identified, along with new animal models of cardiac dysmorphogenesis and an exciting array of genetic tools for further dissection, the need for an integrated morphogenetic concept is acute. Models invoking a linear array of cardiac segments are difficult to reconcile with the observation that those segments are evident only on the outer curvature of the heart tube. Molecular and anatomical evidence supports the view that chamber specification is achieved by interpretation of dorso-ventral (inner curvature/outer curvature), as well as anterior-posterior patterning information in the primary heart tube. In this essay, I examine some of the issues influencing and perhaps confusing our view of cardiac morphogenesis and briefly discuss regulatory genes in the context of an evolving morphogenetic model.