Villin associates with specific microfilamentous structures as seen by immunofluorescence microscopy on tissue sections and cells microinjected with villin

Villin is a major protein of the microfilament bundle which makes up the core of each microvillus of the brush border of the intestinal epithelial cell. Using antibodies to villin in indirect immunofluorescence microscopy on isolated cells and on frozen tissue sections, the protein is readily detectable in the microvilli of the brush border of both intestinal and renal epithelial cells. However, villin could not be detected in tissue culture cells either by immunofluorescence microscopy or by immune replica procedures. When native villin was microinjected into such cells and its distribution visualized by immunofluorescence microscopy, the protein was found to be associated with microfilamentous structures. Moreover, preferential association of the villin into the microfilaments at the leading edges of the living cell was observed. Since villin behaves in vitro as a calcium-regulated F-actin bundling protein, we discuss the possibility that villin is immunologically distinct but functionally related to putative calcium-regulatory factors assumed to be present in cultured cells.