Astrocytes and neurons express the tight junction-specific protein occludin in vitro

The expression of occludin, an integral plasma membrane protein specificall y located at tight junctions, was studied in various epithelial and nonepit helial tissues by means of RT-PCR, Western blotting, and immunofluorescent staining. Besides detection in epithelial and endothelial tissue, expressio n of occludin was found in primary and secondary cultures of neurons and as trocytes. Differentiation of astrocytes in vitro led to a marked decrease i n occludin expression. Extractability of occludin from plasma membranes dif fered considerably between epithelial and nonepithelial cells. Following tr eatment with Triton X-100, occludin was completely extracted from astrocyti c membranes but not from membranes derived from MDCK cells, suggesting a di fference in the cytoplasmic and/or plasma membrane anchoring of occludin be tween these cell types. (C) 1999 Academic Press.