EARLY EXPRESSION OF A NOVEL RADIAL GLIA ANTIGEN IN THE CHICK-EMBRYO

Monoclonal antibody 3CB2 recognizes an antigen expressed in discrete c ell types derived from ectoderm and mesoderm. Biochemical and immunohi stochemical studies indicate that the antigen recognized by the antibo dy is a 55 kDa cytoplasmic protein that may be an intermediate filamen t associated protein (IFAP). Developmental studies show that 3CB2 anti gen is intensely expressed very early in the chick embryo, in the neur al tube, myotomes, and in mesenchymal cells of visceral arches and the presumptive facial area. As development proceeds, antigen expression becomes restricted to astrocytes and radial glia cells throughout the brain. A detailed immunohistochemical study of the developing chick re tina shows that the expression of 3CB2 antigen at embryonic day 8 (E8) is restricted to Muller cells, with the pattern of expression closely related to their degree of differentiation. We show, by immunocytoche mistry labeling of entire Muller cells dissociated from retinas of E16 -E20, that 3CB2 monoclonal is labeling the whole cell. 3CB2 selectivel y labels Muller cells in the rat and chameleon, but not their retinal horizontal cell axons. 3CB2 monoclonal is a very sensitive marker for early differentiating Muller cells. Our results provide evidence that 3CB2 antigen is a cytoskeletal component which may be involved in the morphogenesis of these cells, and also perhaps in the outgrowth of som e axons. (C) 1995 Wiley-Liss, Inc.