Ultrastructural localization of cellular prion protein (PrPc) at the neuromuscular junction

We examined the localization of the normal cellular isoform of prion protei n (PrPc) in mammalian skeletal muscle. Using two anti-PrP antibodies, the n euromuscular junction (NMJ) was preferentially stained after immunohistoflu orescence. The mouse, hamster, and human NMJ displayed a fluorescent signal specific for PrPc, Postembedding immunoelectron microscopy analysis perfor med in the mouse muscle showed that the PrPc-specific colloidal gold immuno labelling was concentrated over the sarcoplasmic cytoplasm, The membrane of the postsynaptic domain was devoid of gold particles, while a weak signal was occasionally observed close to the presynaptic vesicles of the terminal axons, These results indicate that the PrP gene is expressed in mammalian muscle at the NMJ, The subsynaptic sarcoplasm of the NMJ appears to be the privileged site where PrPc presumably associated with endosome membrane may play a role in either physiological activity or maintenance of the morphol ogical integrity of the synapse. J. Neurosci. Res. 55:261-267, 1999. (C) 19 99 Wiley-Liss, Inc.