1 - Cardiac Fate Maps: Lineage Allocation, Morphogenetic Movement, and Cell Commitment

Abstract

Results of fate-mapping experiments and transplantation studies that test the developmental potency of early mesodermal cells have provided new insight into the process of lineage specification in gastrulating chick and mouse embryos. Specifically, cellular ingression and cell movement in the mesoderm through the primitive streak are associated with a restriction in mesodermal potency. During normal development, such a morphogenetic repertoire may be essential for establishing an early association of the heart mesoderm and the gut endoderm. This would ensure that tissues involved in inductive interactions are properly placed during cardiac differentiation. It has been shown in the mouse and chick that different epiblast cell populations have equivalent developmental potencies, which enable them to respond to the cardiogenic signals in the gastrulating embryo following heterotopic transplantation. It is plausible that the initial morphogenetic cell movement associated with germ layer formation is not critical for the specification of heart mesoderm. The necessary signal( s) for myocardial specification may be found only after the cells have reached the cardiogenic field.