NUTRITIONAL REQUIREMENTS OF THE EARLY CHICK EMBRYO. III. THE METABOLIC BASIS OF MORPHOGENESIS AND DIFFERENTIATION AS REVEALED BY THE USE OF INHIBITORS

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Abstract
1. The effects of metabolic inhibitors on the development in vitro of approximately 600 chick blastoderms (definitive primitive streak through 8-somite stages) have been studied. 2. Embryos explanted to glucose media containing either 10-4 to 5 x 10-5M monoiodoacetate or 10-2M fluoride rapidly undergo complete degeneration and disintegration. These effects are reversible by substitution of 2 x 10-2M pyruvate (or lactate) for the glucose. At lower inhibitor concentrations of iodoacetate (2 x 10-3M) the central nervous system degenerates or fails to form, but the heart develops and pulsates. Fluoride has almost the opposite effect: concentrations which cause degeneration of the heart (5 x l0-3M) have no appreciable effect upon the developing central nervous system. 3. Other inhibitors: citrate, malonate, cyanide and azide, produce a differential pattern of inhibition similar to that produced by iodoacetate. Azide, however, does not lead to as clear cut a pattern of differential degeneration. as do the others. 4. Comparison of the effects of inhibitors with those produced by substrate deprivation, low oxygen tension, etc. reveals that all of these environmental modifications give rise to a characteristic pattern of differential degeneration in the blastoderm, the time course and spatial pattern of which is essentially identical with that occurring in the non-nutrient control series; the node and the head-fold, in this order, being the two most sensitive regions. 5. The pattern of differential inhibition of development produced by the presence of inhibitors or other environmental modifications coincides with the pattern of differentiation activity and, presumably, with the pattern of underlying metabolic (enzymatic) activity. 6. Analysis of the experimental results has led to the formulation of a general hypothesis relating developmental activity, energy requirements and enzyme activity to the gradual transformation from one level of structural complexity to the next.