[Show abstract][Hide abstract] ABSTRACT: We have used circular dichroism to study synthetic peptides from two important regions of the prion protein: the N-terminal octa-repeat domain and a highly conserved hydrophobic section. Our results show that the octa-repeat sequence in free solution can adopt a non-random, extended conformation with properties similar to the poly-L-proline type II left-handed helix. We also show that the conformation can be changed by temperature, organic solvents (e.g. acetonitrile) and on binding to phospholipid vesicles. We compared CD data from two peptides corresponding to the hydrophobic region between residues 106 and 136 which contained either methionine or valine at position 129. This variation represents a common polymorphism in humans which has been shown to influence predisposition towards iatrogenic and sporadic CJD. There was no detectable difference between the CD spectra of these peptides irrespective of the solvent conditions we used.
[Show abstract][Hide abstract] ABSTRACT: Creutzfeldt-Jakob disease (CJD) is a transmissible neurodegenerative disorder characterized by the accumulation of aggregates of a cellular protein, PrP, in the brain. In both human and animals, genetic alterations to the gene encoding PrP (PRNP in human) modulate susceptibility to CJD. The recent epidemic of bovine spongi-form encephalopathy in the UK has raised the possibility of transmission from animal produce to humans. To provide a baseline against which to assess possible risk factors, we have determined the frequencies of predisposing mutations and allelic variants in PRNP and their relative contributions to disease. Systematic PRNP genotype analysis was performed on suspected CJD cases referred to the National Surveillance Unit in the UK over the period 1990-1993. Inspection of 120 candidate cases revealed 67 patients with definite and probable CJD, based on clinical and neuropathological criteria. No PRNP mutations were detected in any of the remaining 53 patients assessed as "non-CJD". A disease-associated mutation in the PRNP gene was identified in nine (13.4%) definite and probable cases of CJD, a reliable estimate of the incidence of PRNP-related inherited CJD based on a prospective epidemiological series. Within the group of sporadic CJD patients (lacking PRNP mutations), we confirmed that the genotype distribution with respect to the common methionine/valine (Met/Val) polymorphism at codon 129 within PRNP was significantly different from the normal Caucasian population. The incidence of Met homozygosity at this site was more than doubled and correlated with increased susceptibility to the development of sporadic CJD. Unlike other recent studies, Val homozygosity was also confirmed to be a significant risk factor in sporadic CJD, with the relative risks for the three genotypes Met/Met: Val/Val:Met/Val being 11:4:1.
[Show abstract][Hide abstract] ABSTRACT: Prion diseases are transmissible neurodegenerative conditions of humans and animals. Prions consist principally of a post-translationally modified form of prion protein (PrP), PrP(Sc), which is partly protease resistant. Transmission of prion diseases between species is limited by a 'species barrier' determined in part by the degree of sequence homology between host PrP and inoculated PrP(Sc) (ref.3) and by prion strain type. The epidemic of bovine spongiform encephalopathy (BSE) in the United Kingdom and other countries has led to concerns that transmission to humans may occur by dietary exposure. BSE appears to be caused by a single strain, distinct from those of natural or experimental scrapie, which is also seen in the new prion diseases of cats and ruminants that have presumably arisen from dietary BSE exposure. Here we show that transgenic mice expressing human PrP in addition to mouse PrP can generate human PrP(Sc) and 'human' prions. These mice therefore provide a model to study experimentally the species barrier limiting BSE transmission to humans. Incubation periods to BSE in transgenic mice are not shortened by expression of human PrP, and only mouse PrP(Sc) is produced in response to such challenge.
[Show abstract][Hide abstract] ABSTRACT: The prion protein (PrP) is central to the aetiology of the prion diseases, transmissible neurodegenerative conditions of humans and animals. PrP null mice show abnormalities of synaptic neurophysiology, in particular weakened GABAA receptor-mediated fast inhibition and impaired long-term potentiation in the hippocampus. Here we demonstrate that this PrP null phenotype is rescued in mice with a high copy number of a transgene encoding human PrP but not in low copy number mice, confirming the specificity of the phenotype for loss of function of PrP. The ability of human PrP to compensate for loss of murine PrP will allow direct study of the functional consequences of the 18 human PrP mutations, which cause the inherited prion diseases; this phenotype can now form the basis of the first functional assay for PrP.
[Show abstract][Hide abstract] ABSTRACT: The prion diseases are neurodegenerative conditions, transmissible by inoculation, and in some cases inherited as an autosomal dominant disorder. They include Creutzfeldt-Jakob disease in humans and scrapie and bovine spongiform encephalopathy in animals. The prion consists principally of a post-translationally modified form of a host-encoded glycoprotein (PrPC), designated PrPSc (ref. 1); the normal cellular function of PrPC is, however, unknown. Although PrP is highly conserved among mammals and widely expressed in early embryogenesis, mice homozygous for disrupted PrP genes appear developmentally and behaviourally normal. PrP is a protein anchored to the neuronal surface by glycosylphosphatidylinositol, suggesting a role in cell signalling or adhesion. Here we report that hippocampal slices from PrP null mice have weakened GABAA (gamma-aminobutyric acid type A) receptor-mediated fast inhibition and impaired long-term potentiation. This impaired synaptic inhibition may be involved in the epileptiform activity seen in Creutzfeldt-Jakob disease and we argue that loss of function of PrPC may contribute to the early synaptic loss and neuronal degeneration seen in these diseases.
[Show abstract][Hide abstract] ABSTRACT: SRY encodes the Y-linked testis-determining factor in humans. A predominant 900 bp transcript originates from a single exon
and encompasses the putative SRY coding sequence. We show that in human adult testis SRY transcription involves multiple start
sites. In addition to a previously defined major initiation site, transcripts originating at least 410 bp upstream of this
site were detected. Using a cDNA specific RT - PCR assay, embryonic and adult human tissues were screened for SRY expression.
In humans, SRY transcription is not restricted to the presumptive and the mature gonadal tissues In the embryo and the adult
respectively but can be detected In a range of other locations. Two human cell lines, NTERA-2 cl.D1 (NT2/D1) and Hep G2, have
been Identified which express SRY at similar levels to adult testis. The NT2/D1 SRY transcripts appear to have the same structure
as those in adult testis. HMBA-Induced differentiation of NT2/D1 cells results in a diminution of SRY mRNA, while transcription
of SRY In retinoic acid differentiated NT2/D1 Is unaffected.
No preview · Article · Jan 1994 · Human Molecular Genetics
[Show abstract][Hide abstract] ABSTRACT: The human prion diseases (spongiform encephalopathies) Creutzfeldt-Jakob disease (CJD) and Gerstznann-Sträussler syndrome
(GSS), are neurodegenerative disorders characterised by the accumulation of an abnonnal isoform of the prion protein. The
normal prion protein is a phosphatidyl inositol anchored, membrane bound slaloglycoprotein of widespread tissue distribution
but expressed predominantly in the brain. 15% of prion diseases are autosomal dominant genetic disorders associated with mutations
in the gene encoding the prion protein. To date six pathogenic ammo acid substitutions have been Identified in affected family
members, in addition to five distinct insertlonal events which occur within a region of the protein comprising four tandem
octapeptide repeats. We have Investigated deletions within this region and have Identified three specific deletions. We report
here that these deletions are not associated with CJD and represent a new class of polymorphism within the prion protein gene.
No preview · Article · Jun 1993 · Human Molecular Genetics
[Show abstract][Hide abstract] ABSTRACT: Molecular genetics has led to considerable advances in our understanding of the transmissible spongiform encephalopathies. The identification of pathogenic mutations in the prion protein gene has enabled a molecular reclassification of the familial forms of these diseases, which may now be referred to as inherited prion diseases. Prion diseases of both humans and animals are associated with deposition of an abnormal isoform of a host-encoded protein, the prion protein (PrP). Human prion diseases have inherited, sporadic and acquired forms. A considerable body of evidence now supports the idea that the transmissible agent in these diseases may be an abnormal isoform of the prion protein. The identification of pathogenic mutations in the PrP gene has enabled the identification of cases of inherited prion disease that would not have been recognised using existing clinical and pathological diagnostic criteria. Since marked clinical and neuropathological overlap between the different neurodegenerative disorders is well recognised, PrP gene analysis is of increasing importance in differential diagnosis. Frontal lobe dementia of non-Alzheimer type and Pick's disease share a number of important clinical and pathological features with prion diseases, and could be considered as candidate prion diseases. However, we have not been able to demonstrate either PrP mutations or the presence of the disease-associated isoform of prion protein in several well-characterised families with these disorders.
No preview · Article · May 1993 · Dementia (Basel, Switzerland)
[Show abstract][Hide abstract] ABSTRACT: Inherited forms of prion diseases are associated with mutations in the prion protein gene. A common polymorphism at codon 129 is also implicated in the predisposition of individuals to sporadic or iatrogenic forms of the disease. This update lists all the currently published mutations and polymorphisms together with their clinical phenotypes, and discusses the significance of the codon 129 genotype in inherited, sporadic, and iatrogenic cases. There are two categories of mutation. Insertions of additional numbers of an octapeptide lying within an octapeptide repeat region now account for six variations and there are also six point mutations. The identification of mutations in this gene has lead to a broadening of the spectrum of clinical phenotypes that can be classified as prion diseases and have provided an important tool in the diagnosis of familial dementias.
[Show abstract][Hide abstract] ABSTRACT: There have been remarkably rapid advances in the understanding of prion diseases over the past year. The controversial notion that the transmissible agent may be an abnormal isoform of a host-encoded protein, the prion protein, is now gaining wide acceptance. The conundrum of how a disease can both be inherited as an autosomal dominant condition and also be experimentally transmissible by inoculation is beginning to make sense.
No preview · Article · Jul 1992 · Current Opinion in Genetics & Development
[Show abstract][Hide abstract] ABSTRACT: The human prion diseases, Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler syndrome (GSS), are neurodegenerative diseases that are unique in being both infectious and genetic. Transmission of both diseases and the animal spongiform encephalopathies (for example, scrapie and bovine spongiform encephalopathy) to experimental animals by intracerebral inoculation with brain homogenates is well documented. Despite their experimental transmissibility, missense and insertional mutations in the prion protein gene are associated with both GSS and familial CJD, demonstrating that the human familial cases are autosomal dominant diseases. More than 80% of CJD cases occur sporadically, however, and are not known to be associated with mutations. Here we report that 21 of 22 sporadic CJD cases and a further 19 of 23 suspected sporadic CJD cases are homozygous at the polymorphic amino-acid residue 129; 51% of the normal population are heterozygous at this site. We argue that homozygosity predisposes towards sporadic CJD and that this directly supports the hypothesis that interaction between prion protein molecules underlies the disease process.
[Show abstract][Hide abstract] ABSTRACT: A search of a 35-kilobase region of the human Y chromosome necessary for male sex determination has resulted in the identification of a new gene. This gene is conserved and Y-specific among a wide range of mammals, and encodes a testis-specific transcript. It shares homology with the mating-type protein, Mc, from the fission yeast Schizosaccharomyces pombe and a conserved DNA-binding motif present in the nuclear high-mobility-group proteins HMG1 and HMG2. This gene has been termed SRY (for sex-determining region Y) and proposed to be a candidate for the elusive testis-determining gene, TDF.