REGULATIVE ABILITY OF THE PROSPECTIVE CARDIOGENIC AND VASCULOGENIC AREAS OF THE PRIMITIVE STREAK DURING AVIAN GASTRULATION

Four types of microsurgical experiments were conducted to analyze hear t and blood vessel development during gastrula stages of avian embryos , stages during which prospective cardiogenic and vasculogenic cells r eside within the primitive streak. Experiments addressed whether cells not normally destined to form heart could form heart when given the o pportunity to do so and vice versa; cells destined to form rostral lev els of the heart (or, alternatively, head blood vessels) could form ca udal levels of the heart (or, alternatively, trunk blood vessels) and vice versa; the early endoderm imparts rostrocaudal organization to th e heart and associated blood vessels; and ingression of cells from the primitive streak and their subsequent migration into the mesodermal m antle is a cell-autonomous event for migrating cells. Our results demo nstrate the lability of prospective cardiogenic and vasculogenic cells of the primitive streak, both in terms of the type of mesodermal stru ctures they are capable of forming (or of being formed from) and in te rms of the rostrocaudal patterning of the cardiovascular system. In ad dition, our results show that cell ingression and migration is directe d by environmental cues and is not a cell-autonomous process for migra ting cells. Finally, our results suggest that patterning of the cardio vascular system occurs after cells enter the mesodermal mantle, presum ably through cell-cell inductive interactions. However, the early endo derm is not the primary source of the patterning influence. What is th e source remains to be established. (C) 1993 Wiley-Liss, Inc.