NEUROTHELIN - AMINO-ACID-SEQUENCE, CELL-SURFACE DYNAMICS AND ACTIN COLOCALIZATION

Neurothelin is a cell surface protein of chicken endothelial cells at the blood-brain barrier and also of pigment epithelial cells forming t he blood-eye barrier. Peptide sequencing of affinity-purified neurothe lin revealed that it is likely to be identical with the protein called HT7. It belongs to the immunoglobulin superfamily having two extracel lular CZ-type domains, a membrane spanning region and a cytoplasmic ta il. During development neurothelin cell surface localization changed o n pigment epithelial cells. In early embryogenesis neurothelin was fou nd preferentially at lateral sites of neighboring epithelial cells, bu t after hatching, predominantly on basal cell surfaces and on apical m icrovilli of epithelial cells that contact retinal photoreceptors. Dis ruption of cell-cell contacts induced a rapid change of neurothelin di stribution on the cell surface in vitro as could be shown by confocal laser microscopy Disintegration of microfilaments by cytochalasin D ha mpered this specific cell surface rearrangement of neurothelin, wherea s depolymerization of microtubules by demecolcine had no effect, In do uble-labeling experiments neurothelin and F-actin were colocalized. Th e data suggest that the polarized cell surface distribution of neuroth elin is influenced intracellularly by F-actin and extracellularly by c ell-cell interactions.