CARDIAC LOOPING - AN UNEASY DEAL WITH LATERALITY

Cardiac looping is a key morphogenetic went in vertebrate heart develo pment. In a complex progression, the linear heart tube adopts a sweepi ng rightward curvature, establishing an architecture for the multicham bered organ it soon becomes. Looping is an asymmetric event, its right ward direction being determined by an embryonic left-right axial pathw ay. The dextral loop has been a vehicle for development of heart compl exity during evolution, to the extent that in higher vertebrates and h umans, heart structure and function is extremely susceptible to pertur bations of laterality, which may be common. The first clues to genetic control of laterality and looping are now emerging. Key issues to res olve include the origin of laterality information in the embryo, the e xact nature of the effector molecules that link laterality to looping and the intrinsic mechanisms that drive the looping process itself.