Prion protein (PrPc) immunocytochemistry and expression of the green fluorescent protein reporter gene under control of the bovine PrP gene promoter in the mouse brain

Expression of the cellular prion protein (PrPc) by host cells is required for prion replication and neuroinvasion in transmissible spongiform encephalopathies. As a consequence, identification of the cell types expressing PrPc is necessary to determine the target cells involved in the cerebral propagation of prion diseases. To identify the cells expressing PrPc in the mouse brain, the immunocytochemical localization of PrPc was investigated at the cellular and ultrastructural levels in several brain regions. In addition, we analyzed the expression pattern of a green fluorescent protein reporter gene under the control of regulatory sequences of the bovine prion protein gene in the brain of transgenic mice. By using a preembedding immunogold technique, neuronal PrPc was observed mainly bound to the cell surface and presynaptic sites. Dictyosomes and recycling organelles in most of the major neuron types also exhibited PrPc antigen. In the olfactory bulb, neocortex, putamen, hippocampus, thalamus, and cerebellum, the distribution pattern of both green fluorescent protein and PrPc immunoreactivity suggested that the transgenic regulatory sequences of the bovine PrP gene were sufficient to promote expression of the reporter gene in neurons that express immunodetectable endogenous PrPc. Transgenic mice expressing PrP-GFP may thus provide attractive murine models for analyzing the transcriptional activity of the Prnp gene during prion infections as well as the anatomopathological kinetics of prion diseases. (C) 2004 Wiley-Liss, Inc.