Gene Expression in Scrapie

Abstract

To define genes associated with or responsible for the neurodegenerative changes observed in transmissible spongiform encephalopathies, we analyzed gene expression in scrapie-infected mouse brain using "mRNA differential display." The RNA transcripts of eight genes were increased 3-8-fold in the brains of scrapie-infected animals. Five of these genes have not previously been reported to exhibit increased expression in this disease: cathepsin S, the C1q B-chain of complement, apolipoprotein D, and two previously unidentified genes denominated scrapie-responsive gene (ScRG)-1 and ScRG-2, which are preferentially expressed in brain tissue. Increased expression of the three remaining genes, ␤2 microglobulin, F4/80, and metallothionein II, has previously been reported to occur in experimental scrapie. Kinetic analysis revealed a concomitant increase in the levels of ScRG-1, cathepsin S, the C1q B-chain of complement, and ␤2 microglobulin mRNA as well as glial fibrillary acidic protein and F4/80 transcripts, markers of astrocytosis and microglial activation, respectively. In contrast, the level of ScRG-2, apolipoprotein D, and metallothionein II mRNA was only increased at the terminal stage of the disease. ScRG-1 mRNA was found to be preferentially expressed in glial cells and to code for a short protein of 47 amino acids with a strong hydrophobic N-terminal region.

Characterization of the Human Analogue of a Scrapie-responsive Gene

“…Enhanced expression of ScRG-1 in the brain of scrapie-infected mice occurs concomitantly with increased expression of GFAP mRNA, a marker of astrocytosis (3). Moreover, ScRG-1 mRNA was found to be preferentially expressed in cells of glial origin and to encode a protein with a putative signal peptide (2). These observations suggest that ScRG-1 may play a role in the host response to prion-associated infections.…”

“…Comparison of human and murine cDNA sequences indicated that introduction of a one-nucleotide gap in the murine ORF would generate an open reading frame corresponding to a protein of 98 amino acids the sequence of which would be almost identical to that encoded by the human ScRG-1 cDNA. This prompted us to clone a new mouse brain ScRG-1 cDNA from a lambda library, using as a probe the ScRG-1 cDNA clone 24 previously isolated by RACE (2). The sequence of clone 1 obtained from the library was then determined (Fig.…”

“…Samples of normal human brain and of the brain from a patient diagnosed with CJD were obtained by informed consent, under the auspices of the Program de Recherche sur les Encéphalopathies Spongiformes Sub-aigü es Transmissibles et les Prions (CNRS, France). Human poly(A) ϩ mRNA was obtained as described previously (2). Northern blots were performed using glyoxal denaturation, and the blotted membranes were hybridized using probes radiolabeled to a specific activity of at least 1 ϫ 10 9 cpm/mg, as described previously (2).…”

“…RNA Extraction and Northern Blot Hybridization-RNA was extracted from the brains of either mock infected C57Bl/6 mice or mice infected with the C506M3 strain of scrapie, as described previously (2). Total RNA was extracted by the method of Chirgwin et al (10) from the frontal cortex obtained at autopsy from a patient free from any neurological disease (patient 941005, 46 years old) and from a patient with typical neuropathological findings of sporadic Creutzfeldt-Jakob disease (patient 93005, 59 years old).…”

“…To identify the genes the altered expression of which is associated with or may even be responsible for the neurodegenerative changes observed in TSE, we have systematically analyzed modifications of gene expression in scrapie-infected mouse brain using "mRNA differential display" (2). This approach has led to the detection of an increased level of expression of eight cellular genes.…”