Immunocytochemical localization of α-actinin in intestinal epithelial cells

Abstract

α-Actinin was localized in chicken intestinal epithelial cells by immunofluorescence and immunoferritin labeling of thin frozen sections. Most of the label of the brush border was confined to the terminal web area. The label there was concentrated mainly along the 'roots' of the microvilli core microfilaments and in the vicinity of the zonula adherens. In the latter structure, the narrow electron-dense zones adjacent to the cell membranes, however, were not significantly labeled. This suggests that α-actinin does not mediate directly the association of the transverse terminal web microfilaments to the membrane at the zonula adherens. Sparse ferritin labeling was found near the tight junction, whereas the staining associated with the spot desmosome was negligible. The microvilli were not significantly labeled by either immunofluoresence or immunoferritin staining unless the sections were previously treated with detergent. Moreover, α-actinin (or a structurally related protein) was not detected in preparations of purified microvillar vesicles, suggesting the possibility that the α-actinin staining in the microvilli may be an artifact due to its translocation by the detergent from the terminal web onto the microvilli. The possible roles of α-actinin in the organization and function of the brush border are discussed.