Expression of the cellular prion protein PrPC is sine qua none for the development of transmissible spongiform encephalopathy and thus for the accumulation of the illness-associated conformer PrP Sc . Therefore, the tissue distribution of PrP C at the protein level in both quantitative and qualitative terms was investigated. PrP C was quantified using a two-site enzyme immunometric assay which was calibrated with purified ovine recombinant prion protein (rPrP). The most PrP C -rich tissue was the brain, followed by the lungs, skeletal muscle, heart, uterus, thymus and tongue, which contained between 20-and 50-fold less PrP C than the brain. The PrP C content of these tissues seems to be comparable between sheep. Other organs, however, showed different, but low, levels of the protein depending on the animal examined. This was also the case for tissues from the gastrointestinal tract. The tissue containing the lowest concentration of PrP C was shown to be the liver, where PrP C was found to be between 564-and 16 000-fold less abundant than in the brain. PrP C was concentrated from crude cellular extracts by immunoprecipitation using several monoclonal and polyclonal anti-ovine PrP antibodies. Interestingly, it was observed that the isoform profile of PrP C was tissue-specific. The most atypical electrophoretic profile of PrP C was found in the skeletal muscle, where two polypeptides of 32 and 35 kDa were detected.
IntroductionPrion diseases belong to a family of neurodegenerative disorders that affect both humans and animals. The mechanisms of prion transmission are not yet unravelled. Nevertheless, it is admitted today that one of the fundamental steps in pathogenesis is the conversion of the host-encoded cellular prion protein PrP C into its disease-associated conformer PrP Sc (Prusiner, 1998 ;Jackson & Clarke, 2000). Transmissible spongiform encephalopathies (TSE) are characterized by an accumulation of PrP Sc in the brain and the expression of PrP C has been shown to be crucial for the transmission of the disease and formation of PrP Sc (Bu$ eler et al., 1993 ;Prusiner et al., 1993 ;Weissmann, 1996). One of the emerging hypotheses is that the conversion phenomenon could take place at the site where the infectious agent meets PrP C . The latter has been shown to be expressed in various domains of the hamster brain (Bendheim et al., 1992 ;DeArmond et al., 1999 ;Somerville, 1999) and in several non-neuronal tissues from rodents (Bendheim et al., 1992), cows and humans, including the spleen Author for correspondence : Mohammed Moudjou.Fax j33 1 34 65 26 21. e-mail moudjou!biotec.jouy.inra.fr and lymph nodes (McBride et al., 1992), squamous epithelia of the skin and upper gastrointestinal tract (Pammer et al., 1998(Pammer et al., , 1999. PrP C has also been detected on the surface of lymphocytes in humans and mice (Cashman et al., 1990 ;Mabbott et al., 1997 ;Antoine et al., 2000). A PrP isoform truncated at the C terminus has been detected in mature human and bovine sperm (Shaked et al., 1999). In addition, PrP C m...
