IMMUNOELECTRON MICROSCOPIC ANALYSIS OF A NOVEL CARBOHYDRATE DIFFERENTIATION ANTIGEN (CDA-3C2) IN THE DEVELOPING RAT OLFACTORY AND OTIC SYSTEMS

A carbohydrate differentiation antigen (CDA-3C2) exhibits a highly spe cific and restricted pattern of expression during rat embryogenesis. I n the periphery of the embryo, this antigen is associated transiently with the lateral ectoderm but is retained only in the olfactory and ot ic epithelium throughout morphogenesis. At the light microscopic level , CDA-3C2 immunoreactivity appears mostly along cell periphery and in the extracellular matrix. The aim of the present study was to determin e the specific cellular and subcellular distribution of CDA-3C2 in viv o in order to identify potential sites of cellular and tissue function of the antigen during embryogenesis. There was a strikingly similar s ubcellular distribution of CDA-3C2 in the developing otic and olfactor y systems, found mostly along cell membranes, microvillar projections and acellular secretions of the epithelium. Mature sensory components of the epithelia were not immunoreactive, whereas supportive cells and their secreted structures were densely stained. The highly coincident nature of CDA-3C2 in both sensory epithelia suggests that this carboh ydrate epitope, and possibly its carrier macromolecule, participate in a morphogenetic function common to these two sensory epithelia.