POLYCYSTIN - IN-VITRO SYNTHESIS, IN-VIVO TISSUE EXPRESSION, AND SUBCELLULAR-LOCALIZATION IDENTIFIES A LARGE MEMBRANE-ASSOCIATED PROTEIN

The primary structure of polycystin predicts a large integral membrane protein with multiple cell recognition motifs, but its function remai ns unknown. Insight into polycystin's normal function and its role in the development of autosomal dominant polycystic kidney disease (PKD1) requires the assembly of an extensive collection of molecular reagent s to examine its expression and create model systems for functional st udies, Development of these crucial reagents has been complicated due to the presence of transcriptionally active homologous loci, We have a ssembled the authentic full-length PKD1 cDNA and demonstrated expressi on of polycystin in vitro. Polyclonal antibodies directed against dist inct extra- and intracellular domains specifically immunoprecipitated irt vitro translated polycystin, The panel of antibodies was used to d etermine localization of polycystin in renal epithelial and endothelia l cell lines and tissues of fetal, adult, and cystic origins, In norma l adult kidney and maturing fetal nephrons, polycystin expression was confined to epithelial cells of the distal nephron and vascular endoth elial cells, Expression in the proximal nephron was only observed afte r injury-induced cell proliferation, Polycystin expression was confine d to ductal epithelium in liver, pancreas, and breast, and restricted to astrocytes in normal brain, We report clear evidence for the membra ne localization of polycystin by both tissue sections and by confocal microscopy in cultured renal and endothelial cells, Interestingly, whe n cultured cells made cell-cell contact, polycystin was localized to t he lateral membranes of cells in contact, These data suggest that poly cystin is likely to have a widespread role in epithelial cell differen tiation and maturation and in cell-cell interactions.