Differentiation of Cells of the Rana pipiens Gastrula in Unconditioned Medium1

Abstract

Instances of differentiation in absence of an inductor have multiplied to such extent that the classical picture of embryonic induction is in process of serious re-examination (Grobstein & Parker, 1958; Nieukoop, 1955; Trinkaus & Groves, 1955). Questioned on the basis of the occurrence of neural differentiation without organizer in explants of presumptive epidermis (Barth, 1941; Holtfreter, 1947, 1955; Itô, 1952), the necessity for a specific inductor has proved difficult to demonstrate in other inductive systems. Grobstein & Parker (1958) have shown that tubule formation in metanephrogenic mesenchyme may occur in abnormal sites in vivo without contact with its normal ureteric inductor and even in the anterior chamber of the eye without contact with any other tissue. Niu (1958b) has recently reported a certain percentage of neural differentiation in explants of presumptive epidermis cultured as controls in his salt medium without addition of inductor substances.