α-Actinin-containing branched microvilli isolated from an ascites adenocarcinoma

Microvilli, slender projections approximately 0.1 µm in diameter which occur on the surfaces of many cell types1, are bounded by plasma membrane except at the site of attachment to the cell body and contain microfilament bundle cores. The presence of both microfilaments and plasma membrane suggests the use of microvilli for investigations of membrane cytoskeleton interactions. Immunofluorescence studies with anti-α-actinin2have suggested that α-actinin is concentrated at the tips of intestinal brush border microvilli and might link actin microfilaments and the plasma membrane3. However, this idea was disputed by later immunofluorescence4–7and electrophoresis7studies. To investigate the components and organization of microvilli from a less highly differentiated cell type, we have used an ascites sub-line (MAT-Cl) of a rat mammary tumour, the 13762 mammary adenocarcinoma, whose microvilli are highly branched8,9. Because such unusual structures may provide an understanding of cell-surface assemblies important in determining cell morphology, we have developed a procedure for isolating the branched microvilli and have shown that they contain significant quantities of α-actinin.