A COMMUNITY EFFECT IS REQUIRED FOR AMPHIBIAN NOTOCHORD DIFFERENTIATION

Xenopus mesoderm cells destined to form notochord have been isolated a t various stages of gastrulation and cultured singly or in multicellul ar reaggregates in ectodermal sandwiches. When taken from mid gastrula e, singly implanted notochord progenitor cells can subsequently expres s the notochord marker MZ15. In contrast, the same cells taken from an early gastrula only do so when implanted as groups of such cells. We conclude that the community effect, first described for muscle differe ntiation, also applies to the notochord, and that the time in developm ent when the notochord community effect is required precedes that for muscle.