Localization of Inhibitors of Neural Differentiation in Chick Embryos

Abstract

IN testing the hypothesis of specific inhibition in cellular differentiation, I have shown¹ that early chick embryos, when cultured on a nutrient medium which has incorporated in it supernatants of adult and embryonic brain extracts, displayed homologous brain defects in a significant number of cases. Since the preparation of subcellular components has become a standard technique for problems of cellular chemistry (see review by Allfrey²), this investigation was prompted with the hope of localizing the inhibitory material in the crude brain extracts to a particular cell fraction. Accordingly, chick brains were homogenized and subjected to differential centrifugation in order to obtain mitochondrial, microsomal, and soluble protein fractions. Earlier investigations of Braverman³ and Lenicque⁴ showed that the nuclear fraction is not involved. The procedure used for culturing chick embryos was that of Spratt⁵. Since I have found¹ that stages 4 and 5 (ref. 6) are the crucial stages for treatment with brain extracts, the assay for inhibitory activity was restricted to the use of these stages.