Galactosyltransferase activity of intact neural retinal cells from the embryonic chicken

Abstract

Galactosyltransferase activity was measured on intact embryonic chicken neural retinal cells in a new assay which includes the following: use of [ 3H]UDP-galactose concentrations above the K m; optimization of Mn 2+ and N-acetyl- d-glucosamine concentrations; analysis of the stability of UDP-galactose and N-acetyl- d-glucosamine; control of nucleotide sugar hydrolysis; examination of the effects of serum and trypsin on enzyme activity; product identification; and optimization of cellular health as evidenced by dye-exclusion tests and transmission and scanning electron micrographs. This assay system permits the quantitative comparison of galactosyltransferase activity on different populations of intact embryonic cells. It has been proposed that this enzyme is involved in cellular adhesion, cellular recognition, and differentiation of the cell surface during development. Therefore, enzyme activity was examined as a function of embryonic age, of mitosis versus postmitotic differentiation, and of position along the dorsoventral or nasotemporal axis of the retina. Major findings include: The enzyme activity per cell is twofold higher in the mitotically active margin than in the more differentiated (postmitotic) fundus of the retina; the enzyme activity per cell decreases during the development of the retina; there are no quantitative differences in enzyme activity on cells from nasal, temporal, dorsal, or ventral quadrants or halves of the retina. Possible relationships of these enzyme measurements to cell adhesion, differentiation, and neuronal specification are discussed.