Fig. 5. Patterns of cell movement demonstrate differential requirements for two discrete phases of cardiac fusion in zebrafish. (A) Cardiac fusion begins with a phase of medial cardiomyocyte movement (red arrows). Cardiac cone formation is facilitated by a second phase of regionally restricted angular movement (yellow arrows). (B) In the absence of endocardium, as in clo mutants, medial movement proceeds, but angular movement is lost, resulting in a dysmorphic cardiac cone. (C) In cardia bifida mutants such as mil, medial movement is lost, but angular movement proceeds, resulting in the formation of bilateral cardiac cones. (D) In mil;clo double mutants, all cardiomyocyte movement is lost, indicating a requirement for endocardium for induction of the angular movement observed in mil mutants.