Primitive-streak origin and state of commitment of cells of the cardiovascular system in avian and mammalian embryos.

Early events of cardiovascular development have received renewed interest in recent years. The cardiovascular system is the first major organ system to become functional during early embryogenesis. Cells fated to form the cardiovascular system can be identified as early as during stages of gastrulation of avian and mammalian embryos. In the present brief summary, we describe the primitive-streak origin of the avian cardiovascular system and examine the state of commitment of prospective cardiogenic and vasculogenic areas of the primitive streak. In addition, we describe initial experiments aimed at elucidating the primitive-streak origin of the heart in mouse embryos. Finally, we consider the possible roles of Hensen's node and the "cardiac" endoderm in determination of cell fate and patterning of the avian developing heart tube. Although recent studies have shed considerable light on the origin, migration, and determination of the cardiovascular system, much still remains to be learned about mechanisms underlying cardiovascular patterning in the early embryo.