Marginal zone cells: the primitive streak-inducing component of the primary hypoblast in the chick

Abstract

Removal of both the area opaca and the marginal zone of the area pellucida from a blastoderm stripped of its hypoblast (type-IV operation) prevents the regeneration of a normally functioning primary hypoblast. Stage-XIII E.G & K blastoderms (prior to the appearance of PS) after a type-IV operation do not form a primitive streak. In older type-IV operated blastoderms in which the primitive streak has already begun to appear, the regeneration of a non-functional hypoblast did not support the normal maturation of the primitive streak, and in many cases the already existing rudimentary streak was absorbed. Type-IV operated blastoderms from stage 3+ H & H and on developed normally. It is concluded that the cellular contribution of the marginal zone to the primary hypoblast is instrumental in the latter's capacity to induce a PS.