Recent evidence suggests that structural and functional abnormalities of primary 
cilia in kidney epithelia are associated with mouse and human autosomal dominant 
polycystic kidney disease. To determine whether fibrocystin/polyductin/tigmin 
(FPC), the protein product encoded by the PKHD1 gene that is responsible for 
autosomal recessive polycystic kidney disease among human subjects, is also a 
component of primary cilia in the kidney, antipeptide antibodies to the 
carboxyl-terminal intracellular domain and amino-terminal extracellular domain 
of FPC were generated and were characterized with immunoblotting and 
immuno-light and -electron microscopy. Immunolocalization in normal kidney 
tissue sections and cultured kidney cells demonstrated that FPC was localized to 
the primary cilia and concentrated on the basal bodies in both kidney tissue 
sections and cultured kidney cells. The FPC expression pattern was not altered 
in kidney cells with Pkd1 mutations. These findings suggest that FPC is a 
functional and/or structural component of primary cilia in kidney tubular cells. 
It is proposed that the pathogenesis of autosomal recessive polycystic kidney 
disease is linked to the dysfunction of primary cilia.