Developmental Relationships of Chick Primitive-Streak and Head-Process Stages Explanted to Glucose Media

Abstract

With distinction made between stage 4 of the chick embryo and a somewhat earlier stage which differs only in the lack of cellular condensation in front of Hensen''s node, it was possible to study the development in vitro of stages 3+ (Intermediate streak), 3++ (the new stage), 4 (Definitive streak), and 5 (Head process). Using the Petri-dish method of culture, explants of these stages were cultured for 17-29 hours on media with varying concentrations of glucose and with additions of uniformly labeled glucose-C14 and uranyl nitrate. Explant radioactivity was counted with a Packard tri-carb liquid scintillator or with a Nuclear-Chicago low-background gas flow counter. All explants took in glucose whether or not they developed in vitro. The development of explants varied on "low" and "high" concentrations of glucose. Explants of stages 4 and 5 were unaffected by the high concentration, whereas stage 3++ explants were. In addition to a lower developmental potency, Stage 3++ explants were shown also to differ in sensitivity to the presence of uranyl in the medium. This is interpreted as indicating a change in physiological mechanism for the transport of glucose, from one of passive transport to one of active or enzymatic transport.