Characterization of the bovine prion protein gene: the expression requires interaction between the promoter and intron

Inflammatory mediators reduce surface PrPc on human BMVEC resulting in decreased barrier integrity

The cellular prion protein (PrP^c) is a surface adhesion molecule expressed at junctions of various cell types including brain microvascular endothelial cells (BMVEC) that are important components of the blood-brain barrier (BBB). PrP^c is involved in several physiological processes including regulation of epithelial cell barrier function and monocyte migration across BMVEC. BBB dysfunction and disruption are significant events in central nervous system (CNS) inflammatory processes including HIV neuropathogenesis. Tumor necrosis factor (TNF)-α and vascular endothelial growth factor (VEGF) are two inflammatory factors that have been implicated in the processes that affect BBB integrity. To examine the effect of inflammation on PrP^c expression in BMVEC, we used these mediators and found that TNF-α and VEGF decrease surface PrP^c on primary human BMVEC. We also showed that these factors decrease total PrP^c protein as well as mRNA, indicating that they regulate expression of this protein by de novo synthesis. To determine the effect of PrP^c loss from the surface of BMVEC on barrier integrity, we used small hairpin RNAs to knockdown PrP^c. We found that the absence of PrP^c from BMVEC causes increased permeability as determined by a fluorescein isothiocyanate (FITC)-dextran permeability assay. This suggests that cell surface PrP^c is essential for endothelial monolayer integrity. To determine the mechanism by which PrP^c downregulation leads to increased permeability of an endothelial monolayer, we examined changes in expression and localization of tight junction proteins, occludin and claudin-5, and found that decreased PrP^c leads to decreased total and membrane-associated occludin and claudin-5. We propose that an additional mechanism by which inflammatory factors affect endothelial monolayer permeability is by decreasing cell-associated PrP^c. This increase in permeability may have subsequent consequences that lead to CNS damage.

Modelling neurodegeneration in prion disease - applications for drug development

Prion diseases are a group of neurodegenerative diseases that affect mammals, including humans and ruminants such as sheep. They are believed to be caused by the conversion of the prion protein (PrP), a host expressed protein, into a toxic form (PrP(sc)). PrP(sc) accumulates in the brain, resulting in neuronal loss and the typical spongiform appearance of the brain. So far, there are no effective therapies available for prion diseases. This review discusses possible therapies for prion diseases and the models available for advancing research into the disease.

Sequence variations of the bovine prion protein gene (PRNP) in native Korean Hanwoo cattle

Bovine spongiform encephalopathy (BSE) is one of the fatal neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs) caused by infectious prion proteins. Genetic variations correlated with susceptibility or resistance to TSE in humans and sheep have not been reported for bovine strains including those from Holstein, Jersey, and Japanese Black cattle. Here, we investigated bovine prion protein gene (PRNP) variations in Hanwoo cattle [Bos (B.) taurus coreanae], a native breed in Korea. We identified mutations and polymorphisms in the coding region of PRNP, determined their frequency, and evaluated their significance. We identified four synonymous polymorphisms and two non-synonymous mutations in PRNP, but found no novel polymorphisms. The sequence and number of octapeptide repeats were completely conserved, and the haplotype frequency of the coding region was similar to that of other B. taurus strains. When we examined the 23-bp and 12-bp insertion/deletion (indel) polymorphisms in the non-coding region of PRNP, Hanwoo cattle had a lower deletion allele and 23-bp del/12-bp del haplotype frequency than healthy and BSE-affected animals of other strains. Thus, Hanwoo are seemingly less susceptible to BSE than other strains due to the 23-bp and 12-bp indel polymorphisms.

The 5' flanking region and intron1 of the bovine prion protein gene (PRNP) are responsible for negative feedback regulation of the prion protein

Transcription factors regulate gene expression by controlling the transcription rate. Some genes can repress their own expression to prevent over production of the corresponding protein, although the mechanism and significance of this negative feedback regulation remains unclear. In the present study, we describe negative feedback regulation of the bovine prion protein (PrP) gene PRNP in Japanese Black cattle. The PrP-expressing plasmid pEF-boPrP and luciferase-expressing plasmids containing the partial promoter fragment of PRNP incorporating naturally occurring single-nucleotide or insertion/deletion polymorphisms were transfected into N2a cells. Transfection of pEF-boPrP induced PrP overexpression and decreased the promoter activity of PRNP in the wild-type haplotype (23-bp Del, 12-bp Del, and −47C). Reporter gene assays further demonstrated that the 12- and 23-bp Ins/Del polymorphisms, which are thought to be associated with Sp1 (Specific protein 1) and RP58 (Repressor Protein with a predicted molecular mass of 58 kDa), in intron1 and the upstream region, respectively, and an additional polymorphism (−47C→A) in the Sp1-binding site responded differently to PrP overexpression. With the −47C SNP, the presence of the Del in either the 23-bp Ins/Del or the 12-bp Ins/Del allele was essential for the negative feedback caused by PrP overexpression. Furthermore, deletion mutants derived from the wild-type haplotype showed that nucleotides −315 to +2526, which include the 5′-flanking region and exon1, were essential for the response. These results indicate that certain negative feedback response elements are located in these sequences, suggesting that regulation by transcription factors such as Sp1 and RP58 may contribute to the negative feedback mechanism of PRNP.

Detection and control of prion diseases in food animals

Transmissible spongiform encephalopathies (TSEs), or prion diseases, represent a unique form of infectious disease based on misfolding of a self-protein (PrP^C) into a pathological, infectious conformation (PrP^Sc). Prion diseases of food animals gained notoriety during the bovine spongiform encephalopathy (BSE) outbreak of the 1980s. In particular, disease transmission to humans, to the generation of a fatal, untreatable disease, elevated the perspective on livestock prion diseases from food production to food safety. While the immediate threat posed by BSE has been successfully addressed through surveillance and improved management practices, another prion disease is rapidly spreading. Chronic wasting disease (CWD), a prion disease of cervids, has been confirmed in wild and captive populations with devastating impact on the farmed cervid industries. Furthermore, the unabated spread of this disease through wild populations threatens a natural resource that is a source of considerable economic benefit and national pride. In a worst-case scenario, CWD may represent a zoonotic threat either through direct transmission via consumption of infected cervids or through a secondary food animal, such as cattle. This has energized efforts to understand prion diseases as well as to develop tools for disease detection, prevention, and management. Progress in each of these areas is discussed.

Bovine spongiform encephalopathy associated insertion/deletion polymorphisms of the prion protein gene in the four beef cattle breeds from North China

Two insertion/deletion (indel) polymorphisms of the prion protein gene (PRNP), a 23-bp indel in the putative promoter region and a 12-bp indel within intron I, are associated with the susceptibility to bovine spongiform encephalopathy (BSE) in cattle. In the present study, the polymorphism frequencies of the two indels in four main beef cattle breeds (Hereford, Simmental, Black Angus, and Mongolian) from North China were studied. The results showed that the frequencies of deletion genotypes and alleles of 23- and 12-bp indels were lower, whereas the frequencies of insertion genotypes and alleles of the two indels were higher in Mongolian cattle than in the other three cattle breeds. In Mongolian cattle, the 23-bp insertion / 12-bp insertion was the major haplotype, whereas in Hereford, Simmental, and Black Angus cattle, the 23-bp deletion / 12-bp deletion was the major haplotype. These results demonstrated that Mongolian cattle could be more resistant to BSE, compared with the other three cattle breeds, because of its relatively low frequencies of deletion genotypes and alleles of 23- and 12-bp indel polymorphisms. Thus, this race could be important for selective breeding to improve resistance against BSE in this area.

Evaluation of PRNP expression based on genotypes and alleles of two indel loci in the medulla oblongata of Japanese Black and Japanese Brown cattle

Background

Prion protein (PrP) level plays the central role in bovine spongiform encephalopathy (BSE) susceptibility. Increasing the level of PrP decreases incubation period for this disease. Therefore, studying the expression of the cellular PrP or at least the messenger RNA might be used in selection for preventing the propagation of BSE and other prion diseases. Two insertion/deletion (indel) variations have been tentatively associated with susceptibility/resistance of cattle to classical BSE.

Methodology/Principal Findings

We studied the expression of each genotype at the two indel sites in Japanese Black (JB) and Japanese Brown (JBr) cattle breeds by a standard curve method of real-time PCR. Five diplotypes subdivided into two categories were selected from each breed. The two cattle breeds were considered differently. Expression of PRNP was significantly (p<0.0001) greater in the homozygous deletion genotype at the 23-bp locus in JB breed. Compared to the homozygous genotypes, the expression of PRNP was significantly greater in the heterozygous genotype at the 12-bp locus in JB (p<0.0001) and in JBr (p = 0.0394) breeds. In addition, there was a statistical significance in the PRNP levels between the insertion and the deletion alleles of the 23-bp locus in JB (p = 0.0003) as well as in JBr (p = 0.0032). There was no significance in relation to sex, age, geographical location or due to their interactions (p>0.05).

Conclusion

Our results suggest that the del/del genotype or at least its del allele may modulate the expression of PRNP at the 23-bp locus in the medulla oblongata of these cattle breeds.

The extracellular regulated kinase-1 (ERK1) controls regulated alpha-secretase-mediated processing, promoter transactivation, and mRNA levels of the cellular prion protein

The α-secretases A disintegrin and metalloprotease 10 (ADAM10) and ADAM17 trigger constitutive and regulated processing of the cellular prion protein (PrP(c)) yielding N1 fragment. The latter depends on protein kinase C (PKC)-coupled M1/M3 muscarinic receptor activation and subsequent phosphorylation of ADAM17 on its intracytoplasmic threonine 735. Here we show that regulated PrP(c) processing and ADAM17 phosphorylation and activation are controlled by the extracellular-regulated kinase-1/MAP-ERK kinase (ERK1/MEK) cascade. Thus, reductions of ERK1 or MEK activities by dominant-negative analogs, pharmacological inhibition, or genetic ablation all impair N1 secretion, whereas constitutively active proteins increase N1 recovery in the conditioned medium. Interestingly, we also observed an ERK1-mediated enhanced expression of PrP(c). We demonstrate that the ERK1-associated increase in PrP(c) promoter transactivation and mRNA levels involve transcription factor AP-1 as a downstream effector. Altogether, our data identify ERK1 as an important regulator of PrP(c) cellular homeostasis and indicate that this kinase exerts a dual control of PrP(c) levels through transcriptional and post-transcriptional mechanisms.

PRNP haplotype associated with classical BSE incidence in European Holstein cattle

Background

Classical bovine spongiform encephalopathy (BSE) is an acquired prion disease of cattle. The bovine prion gene (PRNP) contains regions of both high and low linkage disequilibrium (LD) that appear to be conserved across Bos taurus populations. The region of high LD, which spans the promoter and part of intron 2, contains polymorphic loci that have been associated with classical BSE status. However, the complex genetic architecture of PRNP has not been systematically tested for an association with classical BSE.

Methodology/Principal Findings

In this study, haplotype tagging single nucleotide polymorphisms (htSNPs) within PRNP were used to test for association between PRNP haplotypes and BSE disease. A combination of Illumina goldengate assay, sequencing and PCR amplification was used to genotype 18 htSNPs and 2 indels in 95 BSE case and 134 control animals. A haplotype within the region of high LD was found to be associated with BSE unaffected animals (p-value = 0.000114).

Conclusion/Significance

A PRNP haplotype association with classical BSE incidence has been identified. This result suggests that a genetic determinant in or near PRNP may influence classical BSE incidence in cattle.

Intron 1 mediated regulation of bovine prion protein gene expression: Role of donor splicing sites, sequences with potential enhancer and suppressor activities

Prion protein plays a key role in the pathogenesis of transmissible spongiform encephalopathies. Because changes in expression of the prion protein gene (PRNP) alter the incubation time and severity of prion diseases. Our previous work revealed a strong association between the promoter (spanning base pairs (bp) -88 to -30) and intron 1 (spanning bp +114 to +892) that leads to optimum expression of the bovine PRNP. Here, we employed two mutation analysis strategies (deletion and insertion) and two reporter assay systems (luciferase and GFP expression) to define the regulatory domains within intron 1 and further elucidate its role in regulating the promoter activity of the bovine prion protein gene. We identified DNA sequences with potential suppressor and enhancer activities within the 5' end of intron 1. Moreover stability analyses for PRNP mRNAs demonstrated that splicing sites and mechanism are critical for bovine PRNP expression.

Activation and repression of prion protein expression by key regions of intron 1

Expression of the prion protein is necessary for infection with prion diseases. Altered expression levels may play an important role in susceptibility to infection. Therefore, understanding the mechanisms that regulate prion protein expression is of great importance. It was previously shown that expression of the prion protein is to some degree regulated by an alternative promoter within intron 1. Studies using GFP and luciferase reporter systems were undertaken to determine key sites for the repression and activation of expression of the prion protein driven by intron 1. We identified a region within intron 1 sufficient to drive prion protein expression. Our findings highlight two potential repressor regions. Both regions have binding sites for the known repressor Hes-1. Hes-1 overexpression caused a dramatic decrease in PrP protein expression. Additionally, we have identified Atox-1 as a transcription factor that upregulates prion protein expression. These findings clearly indicate that intron 1 plays a key role in regulation of prion protein expression levels.

Two adjacent nuclear factor-binding domains activate expression from the human PRNP promoter

Background

The transmissible spongiform encephalopathies (TSEs) comprise a group of fatal degenerative neurological diseases in humans and other mammals. After infection, the cellular prion protein isoform PrP^C is converted to the pathological PrP^SC scrapie isoform. The continued conversion of PrP^C to PrP^SC requires de novo endogenous PrP synthesis for disease progression. The human prion protein gene (PRNP) promoter was therefore investigated to identify regulatory elements that could serve as targets for therapeutic intervention.

Findings

The human prion protein gene (PRNP) promoter from position -1593 to +134 relative to the putative transcriptional start site (+1) was analyzed by transient transfection in HeLa cells. Deletions from the 5' end between positions -1593 and -232 yielded little change in activity. A further 5' deletion at position -90 resulted in a decline in activity to a level of about 30% of the full-length value. DNase I footprinting of the region between positions -259 and +2 identified two adjacent protected domains designated as prpA (-116 to -143) and prpB (-147 to -186). Internal deletions combined with mobility shift electrophoresis and methylation interference assays indicated the presence of sequence specific nuclear factor complexes that bind to the prpA and prpB domains and activate expression from the human PRNP promoter in an additive fashion.

Conclusion

Results from transient transfection, DNase I footprinting, mobility shift electrophoresis, and methylation interference experiments suggest that two DNase I protected domains designated as prpA and prpB are binding sites for as yet unidentified regulatory factors that independently activate expression from the PRNP promoter.

Ovine PRNP untranslated region and promoter haplotype diversity

The diversity and possible contribution of non-coding regions of the prion protein (PrP) gene (PRNP) to transmissible spongiform encephalopathy susceptibility and PrP regulation are not fully known. This study defined ten ovine PRNP promoters and five untranslated region (UTR) haplotypes found in atypical and classical scrapie cases and healthy control sheep. A greater diversity of promoter and UTR haplotypes was observed in conjunction with the ARQ PrP allele (seven promoter and four UTR haplotypes), while it was observed that the other alleles were linked with a limited number of haplotypes, such as ARR, found to be linked to only two promoter and one UTR haplotypes. In silico analysis identified potential transcription factor binding sites that differed in the promoter haplotype variants. Furthermore, a 5′ UTR internal ribosome entry site motif was identified in exon 2 and highlights a possible role for this exon in regulating PrP expression at the translational level.

Identification of adjacent binding sites for the YY1 and E4BP4 transcription factors in the ovine PrP (Prion) gene promoter

The PrP gene encodes the cellular isoform of the prion protein (PrP(c)) which has been shown to be crucial to the development of transmissible spongiform encephalopathies (TSEs). PrP knock-out mice, which do not express endogenous PrP(c), exhibit resistance to TSE disease. The regulation of PrP gene expression represents, therefore, a crucial factor in the development of TSEs. Two sequence motifs in the PrP promoter (positions -287 to -263 from transcriptional start) were previously reported as being highly conserved, and it was suggested that they represent binding sites for as yet unidentified transcription factors. To test this hypothesis, binding of nuclear proteins was analyzed by electrophoretic mobility shift assays using ovine or murine cells and tissues with radiolabeled DNA probes containing the conserved motif sequences. Specific binding was observed to both motifs, and polymorphic variants of these motifs exhibited differential binding. Two proteins bound to these motifs were identified as the Yin Yang 1 (YY1) (motif 1) and E4BP4 (motif 2) transcription factors. Functional promoter analysis of four different promoter variants revealed that motif 1 (YY1) was associated with inhibitory activity in the context of the PrP promoter, whereas motif 2 (E4BP4) was linked to a slight enhancing activity. This represents the first demonstration of binding of nuclear factors to two highly conserved DNA sequence motifs within mammalian PrP promoters. The action of these factors on the PrP promoter is haplotype-specific, leading us to propose that the prion protein expression pattern and, with it, the distribution of TSE infectivity may be associated with PrP promoter genotype.

In silico comparative analysis of DNA and amino acid sequences for prion protein gene

Genetic variability might contribute to species specificity of prion diseases in various organisms. In this study, structures of the prion protein gene (PRNP) and its amino acids were compared among species of which sequence data were available. Comparisons of PRNP DNA sequences among 12 species including human, chimpanzee, monkey, bovine, ovine, dog, mouse, rat, wallaby, opossum, chicken and zebrafish allowed us to identify candidate regulatory regions in intron 1 and 3'-untranslated region (UTR) in addition to the coding region. Highly conserved putative binding sites for transcription factors, such as heat shock factor 2 (HSF2) and myocite enhancer factor 2 (MEF2), were discovered in the intron 1. In 3'-UTR, the functional sequence (ATTAAA) for nucleus-specific polyadenylation was found in all the analysed species. The functional sequence (TTTTTAT) for maturation-specific polyadenylation was identically observed only in ovine, and one or two nucleotide mismatches in the other species. A comparison of the amino acid sequences in 53 species revealed a large sequence identity. Especially the octapeptide repeat region was observed in all the species but frog and zebrafish. Functional changes and susceptibility to prion diseases with various isoforms of prion protein could be caused by numeric variability and conformational changes discovered in the repeat sequences.

Physiology of the prion protein

Prion diseases are transmissible spongiform encephalopathies (TSEs), attributed to conformational conversion of the cellular prion protein (PrP(C)) into an abnormal conformer that accumulates in the brain. Understanding the pathogenesis of TSEs requires the identification of functional properties of PrP(C). Here we examine the physiological functions of PrP(C) at the systemic, cellular, and molecular level. Current data show that both the expression and the engagement of PrP(C) with a variety of ligands modulate the following: 1) functions of the nervous and immune systems, including memory and inflammatory reactions; 2) cell proliferation, differentiation, and sensitivity to programmed cell death both in the nervous and immune systems, as well as in various cell lines; 3) the activity of numerous signal transduction pathways, including cAMP/protein kinase A, mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt pathways, as well as soluble non-receptor tyrosine kinases; and 4) trafficking of PrP(C) both laterally among distinct plasma membrane domains, and along endocytic pathways, on top of continuous, rapid recycling. A unified view of these functional properties indicates that the prion protein is a dynamic cell surface platform for the assembly of signaling modules, based on which selective interactions with many ligands and transmembrane signaling pathways translate into wide-range consequences upon both physiology and behavior.

Coordinate regulation of bovine prion protein gene promoter activity by two Sp1 binding site polymorphisms

Relationships between insertion/deletion (Ins/Del) polymorphisms of the bovine prion protein gene (PRNP) promoter and bovine spongiform encephalopathy (BSE) susceptibility have been reported. Our previous study has shown that polymorphisms of -6C-->T included in the specific protein 1 (Sp1) site in the 5'-flanking region of bovine PRNP influence the promoter activity of bovine PRNP. The present study shows that 12 and 23bp Ins/Del polymorphisms in the upstream region and an additional polymorphism (-47C-->A) in the Sp1 binding site coordinately affect the promoter activity. Reporter gene assays demonstrated that the bovine PRNP promoter containing -47A and 23bp Del/12bp Ins or 23bp Ins/12bp Ins showed lower promoter activity compared with other haplotypes (23bp Del/12bp Ins or 23bp Ins/12bp Del with -47C) or the wild-type haplotype (23bp Del/12bp Del with -47C). Furthermore, gel shift assays showed that the binding activity of Sp1 to the PRNP promoter was influenced by both polymorphisms with corresponding effects on the promoter activity. The coordinate regulation of the bovine PRNP promoter suggests the two Sp1 binding site polymorphisms control Sp1 binding to the PRNP promoter and its activity.

Characterization of prion susceptibility in Neuro2a mouse neuroblastoma cell subclones

In this study, we established Neuro2a (N2a) neuroblastoma subclones and characterized their susceptibility to prion infection. The N2a cells were treated with brain homogenates from mice infected with mouse prion strain Chandler. Of 31 N2a subclones, 19 were susceptible to prion as those cells became positive for abnormal isoform of prion protein (PrP(Sc)) for up to 9 serial passages, and the remaining 12 subclones were classified as unsusceptible. The susceptible N2a subclones expressed cellular prion protein (PrP(C)) at levels similar to the parental N2a cells. In contrast, there was a variation in PrP(C) expression in unsusceptible N2a subclones. For example, subclone N2a-1 expressed PrP(C) at the same level as the parental N2a cells and prion-susceptible subclones, whereas subclone N2a-24 expressed much lower levels of PrP mRNA and PrP(C) than the parental N2a cells. There was no difference in the binding of PrP(Sc) to prion-susceptible and unsusceptible N2a subclones regardless of their PrP(C) expression level, suggesting that the binding of PrP(Sc) to cells is not a major determinant for prion susceptibility. Stable expression of PrP(C) did not confer susceptibility to prion in unsusceptible subclones. Furthermore, the existence of prion-unsusceptible N2a subclones that expressed PrP(C) at levels similar to prion-susceptible subclones, indicated that a host factor(s) other than PrP(C) and/or specific cellular microenvironments are required for the propagation of prion in N2a cells. The prion-susceptible and -unsusceptible N2a subclones established in this study should be useful for identifying the host factor(s) involved in the prion propagation.

Biological characteristics of Chinese hamster ovary cells transfected with bovine Prnp

A normal prion protein (PrP^c) is converted to a protease-resistant isoform by an apparent self-propagating activity in transmissible spongiform encephalopathy, a neurodegenerative disease. The cDNA encoding open reading frame (ORF) of the bovine prion protein gene (Prnp) was cloned from Korean cattle by PCR, and was transfected into Chinese hamster ovary (CHO-K1) cells using lipofectamine. The gene expression of the cloned cDNA was confirmed by RT-PCR and Western blotting with the monoclonal antibody, 6H4. Cellular changes in the transfected CHO-K1 cells were investigated using parameters such as MTT, lactate dehydrogenase (LDH), and superoxide dismutase (SOD) activities, as well as nitric oxide (NO) production, and an apoptosis assay. In the MTT and LDH assays, the bovine PrnP-transfectant showed a lower proliferation rate than the wild-type (p < 0.05). Production of NO, after LPS or ConA stimulation, was not detected in either transfectants or CHO-K1 cells. In SOD assay under ConA stimulation, the SOD activity of transfectants was 10 times higher than that of CHO-K1 cells at 6 h after treatment (p < 0.05). The genomic DNA of both the transfectants and control cells began to be fragmented at 6 h after treatment with cyclohexamide. Caspase-3 activity was reduced by transfection with the bovine Prnp (p < 0.05). Conclusively, the viability of transfectants expressing exogenous bovine Prnp was decreased while the capacities for cellular protection against antioxidative stress and apoptosis were increased.

Genotype distribution of the prion protein gene (PRNP) promoter polymorphisms in Korean cattle

Recently, an association between bovine spongiform encephalopathy (BSE) and insertion/deletion (indel) polymorphisms in the bovine prion protein gene (PRNP) promoter region has been reported in German cattle. These PRNP polymorphisms cause changes in PRNP expression and are thought to play an important role in BSE susceptibility. BSE has been reported in British and Japanese Holstein cattle but has not been diagnosed in Hanwoo cattle (Bos taurus coreanae) up to now. These results prompted us to investigate the genotype distributions of these PRNP promoter polymorphisms in 107 Hanwoo cattle and 52 Holstein cattle and compare the results with those of previous studies. A significant difference (P=0.0249) in allele frequency of the 23 bp indel polymorphism was observed between Hanwoo and the BSE-affected German cattle previously investigated. There were no significant differences in the genotype (P=0.2095) or allele (P=0.8875) frequencies of the 12 bp indel polymorphism between Hanwoo and BSE-affected German cattle. Interestingly, the genotype and allele frequencies of the 23 bp indel polymorphism in Korean Holsteins were very similar to those previously reported for BSE-affected German cattle and healthy US cattle sires.

Regulation of prion protein expression by noncoding regions of the Prnp gene

Expression of the cellular prion protein is necessary for the transmission and propagation of prion diseases. Increasing the level of prion protein expression decreases the incubation period for these diseases. Therefore, understanding the regulation of prion protein expression could be critical for treating or preventing these diseases. We investigated the regulation of prion protein expression by the promoter and noncoding regions of the bovine and murine Prnp genes. We determined that expression is modulated by intron 1 and exon 1. In the absence of intron1, exon 1 inhibited activity of the promoter. However, intron 1 demonstrated promoter-like activity and possessed a TATA box. In addition, we identified an alternative transcript present in the brains of cattle and mice that lacks exon 1. Taken together, these results show that intron 1 and exon 1 play a critical role in the regulation of prion protein expression. Because switching off prion protein expression has been shown to arrest prion disease, these regions present novel targets for intervention in the disease process.

Novel single nucleotide polymorphisms in the specific protein 1 binding site of the bovine PRNP promoter in Japanese Black cattle: impairment of its promoter activity

Susceptibility to transmissible spongiform encephalopathy and different alleles of the prion protein gene (PRNP) of humans and sheep are associated. A tentative association between PRNP promoter polymorphisms and bovine spongiform encephalopathy (BSE) susceptibility has been reported in German cattle, whereas none of the known polymorphisms within the bovine PRNP-coding sequence affect BSE susceptibility. In the present study, novel single nucleotide polymorphisms located in the 5'-flanking region of bovine PRNP affecting its expression were demonstrated in Japanese Black cattle. We sequenced exon 1, and the approximately 200-bp 5'-flanking region of the PRNP translation initiation site containing the proximal promoter of PRNP was harvested. We identified 7 single nucleotide polymorphisms: -184A-->G, -141T-->C, -85T-->G, -47C-->A, -6C-->T, +17C-->T and +43C-->T. Six segregated haplotypes in the population were cloned into luciferase-expressing plasmids, transfected into N2a cells, and their reporter activities were measured 48 h after transfection. Six haplotypes showed a decreased expression level including -6C-->T in specific protein 1 binding site (p < 0.05) or -141T-->C (p < 0.01) at 48 h compared with the wild-type haplotype. These results advocate that certain polymorphisms such as specific protein 1 binding site polymorphisms in the bovine PRNP promoter region in Japanese Black cattle could influence promoter activity, suggesting that breeding cattle with such substitutions may be a useful approach in reducing BSE risk.

Functional relevance of DNA polymorphisms within the promoter region of the prion protein gene and their association to BSE infection

Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative diseases that can occur spontaneously or can be caused by infection or mutations within the prion protein gene PRNP. Nonsynonymous DNA polymorphisms within the PRNP gene have been shown to influence susceptibility/resistance to infection in sheep and humans. Analysis of DNA polymorphisms within the core promoter region of the PRNP gene in four major German bovine breeds resulted in the identification of both SNPs and insertion/deletion (indel) polymorphisms. Comparative genotyping of both controls and animals that tested positive for bovine spongiform encephalopathy (BSE) revealed a significantly different distribution of two indel polymorphisms and two SNPs within Braunvieh animals, suggesting an association of these polymorphisms with BSE susceptibility. The functional relevance of these polymorphisms was analyzed using reporter gene constructs in neuronal cells. A specific haplotype near exon 1 was identified that exhibited a significantly lower expression level. Genotyping of nine polymorphisms within the promoter region and haplotype calculation revealed that the haplotype associated with the lowest expression level was underrepresented in the BSE group of all breeds compared to control animals, indicating a correlation of reduced PRNP expression and increased resistance to BSE.

Comparison of DNA variants in the PRNP and NF1 regions between bovine spongiform encephalopathy and control cattle

DNA from 252 bovine spongiform encephalopathy (BSE) cattle and 376 non-diseased control cattle were genotyped for nine loci in the prion protein (PRNP) gene region, three loci in the neurofibromin 1 (NF1) region and four control loci on different chromosomes. The allele and genotype frequencies of the control loci were similar in BSE and control cattle. In the analysed 7.4 Mb PRNP region, the largest differences between BSE and control cattle were found for the loci REG2, R16 and R18, which are located between +300 and +5600 bp, spanning PRNP introns 1 to 2. Carriers of the REG2 genotype 128/128 were younger at BSE diagnosis than those with the other genotypes (128/140 or 140/140). The predominant haplotype REG2 128 bp-R18 173 bp occurred more frequently (P < 0.001), and the second-most frequent haplotype (REG2 140 bp-R18 175 bp) occurred less frequently (P < 0.05) in BSE than in control cattle. The largest frequency differences between BSE and control groups were observed in the Brown Swiss breed. Across all breeds, most of the same alleles and haplotypes of the PRNP region were associated with BSE. In the 23-cM NF1 region, associations with BSE incidence were found for the RM222 allele and for the DIK4009 genotype frequencies. Cattle carrying RM222 genotypes with the 127- or 129-bp alleles were about half a year older at BSE incidence than those with other genotypes. Across the breeds, different alleles and genotypes of the NF1 region were associated with BSE. The informative DNA markers were used to localize the genetic disposition to BSE and may be useful for the identification of the causative DNA variants.

Regulatory sequences of the PRNP gene influence susceptibility to sporadic Creutzfeldt-Jakob disease

The prion diseases are fatal neurodegenerative disorders that afflict both humans and animals. They comprise kuru, Creutzfeldt-Jakob disease (CJD), Gerstmman-Straussler-Scheinker syndrome (GSS), and fatal familial insomnia (FFI). Both GSS, FFI and approximately 10% of CJD cases are genetically linked disorders, whereas 90% of CJD cases are not associated with mutations in the PRNP coding region, therefore other factors must be involved in pathogenesis of these forms of CJD. There is strong evidence that in transgenic mice the level of PrP gene expression influences the initiation and progression of the prion diseases. Moreover, in in vitro experiments demonstrated that mutations in the regulatory region of PRNP gene altered gene expression, therefore it may be expected that PrP expression level influences the susceptibility to CJD. In order to investigate whether single nucleotide polymorphisms within regulatory region of PRNP may modulate genetic susceptibility to sporadic CJD we examined an association of the C/G polymorphism at position -101 with the sCJD. In our study -101G polymorphism is over-represented among sCJD PRNP codon 129M/V cases compared with the control group. Our data suggest that polymorphism at position -101 in the regulatory region of PRNP may be a risk factor for sCJD among codon 129 heterozygotes.

Sequence variation of bovine prion protein gene in Japanese cattle (Holstein and Japanese Black)

To assess relationships between nucleotide polymorphisms of the prion protein (PRNP) gene and susceptibility to bovine spongiform encephalopathy (BSE), we investigated polymorphisms in the open reading frame (ORF) and 2 upper regions of the PRNP gene from 2 Japanese cattle breeds: 863 healthy Holstein cattle, 6 BSE-affected Holstein cattle, and 186 healthy Japanese Black (JB) cattle. In the ORF, we found single-nucleotide polymorphisms (SNPs) at nucleotide positions 234 and 576 and found 5 or 6 copies of the octapeptide repeat, but we did not find any amino acid substitutions. In the upper region, we examined 2 sites of insertion/deletion (indel) polymorphisms: a 23-bp indel in the upper region of exon 1, and a 12-bp indel in the putative promoter region of intron 1. A previous report suggests that the 23-bp indel polymorphism is associated with susceptibility to BSE, but we did not find a difference in allele frequency between healthy and BSE-affected Holstein cattle. There were differences in allele frequency between healthy Holstein and JB cattle at the 23- and 12-bp indels and at the SNPs at nucleotide positions 234 and 576, but there was no difference in allele frequency of the octapeptide repeat. We identified a unique PRNP gene lacking a 288-bp segment (96 amino acids) in DNA samples stocked in our laboratory, but this deletion was not found in any of the 1049 cattle examined in the present study. The present results provide data about variations and distribution of the bovine PRNP gene.

New ovine PrP gene haplotypes as a result of single nucleotide polymorphisms in the PrP gene promoter

Incidence of scrapie in sheep is strongly associated with PrP gene amino acid codon variants at positions 136, 154 and 171. However, there are breed differences in disease linkage and anomalous disease patterns which cannot obviously be explained by the '3 codon' genotype. Mouse studies indicate that PrP protein levels can influence scrapie disease progression and this prompted us to study the sheep PrP gene promoter region in a search for novel polymorphisms which may influence gene expression and hence disease susceptibility. The incidence of three single nucleotide polymorphisms (SNP) at positions C/A-5354, T/C-5382 and C/G-5622 within the PrP gene promoter region was determined from Neuropathogenesis Unit (NPU) and New Zealand (NZ) Cheviot and UK and NZ Suffolk sheep. The SNP variants A-5354 and G-5622 created consensus sequences for STAT and SP1 transcription factors, respectively, and C-5382 was within Motif 1, one of four conserved motifs found within the promoter region of mammalian PrP genes. The occurrence of C/A-5354 and T/C-5384 SNP exhibited differential associations with the PrP open reading frame (ORF) variants linked to scrapie susceptibility. A significant imbalance in the incidence of the C-5354/AXQ haplotype was found in the NPU Cheviot flock. C-5382 was not found in Suffolk sheep of either UK or NZ origin. The G-5622 SNP was found at a lower incidence in Suffolk sheep compared with Cheviots. The range of transcription factor binding motif profiles in the PrP gene promoter may act to modulate PrP gene activity and warrants further large-scale study.

Comparative PRNP genotyping of U.S. cattle sires for potential association with BSE

The recent discovery of significant associations between bovine spongiform encephalopathy (BSE) susceptibility in German cattle and the frequency distributions of insertion/deletion (indel) polymorphisms within the bovine PRNP gene prompted an evaluation of 132 commercial U.S. artificial insemination (AI) sires from 39 breeds. Forward primer sequences from published primer sets targeting indels within the putative bovine PRNP promoter, intron 1, and the 3' UTR (untranslated region) were synthesized with unique 5' fluorescent labels and utilized to develop a rapid multiplexed PCR assay for identifying BSE-associated indels as well as facilitating polymorphism analyses and/or marker-assisted selection. Significant differences ( p < 0.05 all tests) were detected between the frequencies of bovine PRNP promoter alleles for 48 healthy German cattle previously described and 132 commercial U.S. cattle sires. The frequency of the 23-bp promoter allele observed for commercial U.S. cattle sires strongly resembled that recently described for 43 BSE-affected German cattle. No significant difference ( p = 0.051) was detected between the distributions of promoter genotypes for healthy German cattle and our panel of commercial U.S. cattle sires. Interestingly, significant differences ( p < 0.01; p < 0.02) were also noted between the frequencies and distributions of intron 1 alleles and genotypes, respectively, for BSE-affected German cattle and our panel of U.S. cattle sires. No significant allelic or genotypic differences were detected for the 14-bp 3' UTR indel for any given comparison between German cattle and commercial U.S. cattle sires.

Bovine prion protein gene (PRNP) promoter polymorphisms modulate PRNP expression and may be responsible for differences in bovine spongiform encephalopathy susceptibility

The susceptibility of humans to the variant Creutzfeldt-Jakob disease is greatly influenced by polymorphisms within the human prion protein gene (PRNP). Similar genetic differences exist in sheep, in which PRNP polymorphisms modify the susceptibility to scrapie. However, the known coding polymorphisms within the bovine PRNP gene have little or no effect on bovine spongiform encephalopathy (BSE) susceptibility in cattle. We have recently found a tentative association between PRNP promoter polymorphisms and BSE susceptibility in German cattle (Sander, P., Hamann, H., Pfeiffer, I., Wemheuer, W., Brenig, B., Groschup, M., Ziegler, U., Distl, O., and Leeb, T. (2004) Neurogenetics 5, 19-25). A plausible hypothesis explaining this observation could be that the bovine PRNP promoter polymorphisms cause changes in PRNP expression that might be responsible for differences in BSE incubation time and/or BSE susceptibility. To test this hypothesis, we performed a functional promoter analysis of the different bovine PRNP promoter alleles by reporter gene assays in vitro and by measuring PRNP mRNA levels in calves with different PRNP genotypes in vivo. Two variable sites, a 23-bp insertion/deletion (indel) polymorphism containing a RP58-binding site and a 12-bp indel polymorphism containing an SP1-binding site, were investigated. Band shift assays indicated differences in transcription factor binding to the different alleles at the two polymorphisms. Reporter gene assays demonstrated an interaction between the two postulated transcription factors and lower expression levels of the ins/ins allele compared with the del/del allele. The in vivo data revealed substantial individual variation of PRNP expression in different tissues. In intestinal lymph nodes, expression levels differed between the different PRNP genotypes.

Functional mapping of the bovine Doppel gene promoter region

The PRND gene encodes Doppel (Dpl), a protein that is strongly expressed in testis and at much lower levels in other tissues. Despite the recent discovery of Dpl involvement in spermiogenesis and in apoptotic death of cerebellar neurons, respectively in wild type and transgenic mice, the physiological role of this prion-like protein remains unknown. To better understand which factors may contribute to the modulation of PRND activity, a study of the bovine promoter region was performed. First, the transcription start site of PRND mRNA was identified using an innovative fluorescently labelled oligonucleotide extension (FLOE) method. The initiation site mapped 129 nt upstream of the protein coding sequence and represents a refinement of a previous assignment based on RACE. Second, deletion mutants of the 4530 nt encompassing 2704 nt 5' of the bovine PRND, exon 1, intron 1, and the first 6 nt of exon 2, have been investigated with CAT-reporter assays in order to identify critical elements for the activation of the gene. The results showed that the region -323/+32 (+1 is the transcription start site mapped by FLOE) represents the promoter region and contains positive cis-acting elements (CCAAT and E box) confirming previous reports with the mouse gene. Additional regulatory elements, including binding sites for repressor molecules, have been identified upstream of that region and in the first portion of intron 1, suggesting a complex tissue-specific regulation of Doppel gene expression.

Analysis of sequence variability of the bovine prion protein gene (PRNP) in German cattle breeds

Different alleles of the prion protein gene (PRNP) of human and sheep are known to be associated with varying susceptibilities to transmissible spongiform encephalopathies. However, no polymorphisms in the bovine PRNP gene with an effect on susceptibility to prion diseases have been identified to date. In this study we investigated such polymorphisms in German cattle; 48 healthy animals from six different German cattle breeds and 43 cattle with bovine spongiform encephalopathy (BSE) were analyzed. In contrast to previous studies, all three exons as well as the promoter region of the PRNP gene were investigated. Sequence variants in the bovine PRNP gene could have an impact on the amino acid sequence or the expression level of the prion protein and thus on susceptibility to BSE. We identified a total of 60 polymorphisms in the PRNP gene of German cattle. Of these 60 polymorphisms, 36 were newly identified, whereas 24 of these polymorphisms had been described previously. We did not detect any novel polymorphisms affecting the amino acid sequence of the prion protein. However, we identified a 23-bp insertion/deletion polymorphism in the putative PRNP promoter region that shows a significant association with BSE susceptibility in our animals.

Sequence variation in the bovine and ovine PRNP genes

A resequencing approach was adopted to identify sequence variants in the PRNP gene that may affect susceptibility or resistance to bovine spongiform encephalopathy. The entire PRNP gene (>21 kb) was sequenced from 26 chromosomes from a group of Holstein-Friesian cows, as well as exon 3 of PRNP (>4 kb) from a further 24 chromosomes from six diverse breeds. We identified 51 variant sequences of which 42 were single nucleotide polymorphisms and nine were insertion/deletion (indel) events. The study was extended to exon 3 of the sheep PRNP gene where 23 sequence variants were observed, four of which were indels. The level of nucleotide diversity in the complete bovine PRNP gene was pi = 0.00079, which is similar to that found at the bovine T-cell receptor alpha delta joining region (pi = 0.00077), but somewhat less than that observed for the bovine leptin (pi = 0.00265). Sequence variation within exon 3 of PRNP in both cattle (pi = 0.00102) and sheep (pi = 0.00171) was greater than that for the complete PRNP gene, with sheep showing greater sequence variation in exon 3 than cattle. The level of sequence variation reported here is greater than previously thought for the bovine PRNP gene in cattle. This study highlights the contribution that recombination plays in increasing allelic diversity in this species.

PRNP contains both intronic and upstream regulatory regions that may influence susceptibility to Creutzfeldt-Jakob Disease

The Prion protein (PrP) plays a central role in Creutzfeldt-Jakob Disease (CJD) and other transmissible spongiform encephalopathies (TSEs). Mutations in the protein coding region of the human PrP gene (PRNP), which have been proposed to alter the stability of the PrP protein, have been linked to a number of forms of TSE. However, the majority of CJD cases are not associated with mutations in the PRNP coding region and alternative mechanisms must therefore underlie susceptibility to these forms of CJD. Transgenic mice, that over- or under-express PrP genes, have shown a correlation between the level of PrP gene expression and the incubation time of disease. Polymorphisms that lead to alterations in human PRNP gene expression, could therefore be candidates for influencing susceptibility of an individual to CJD. In order to investigate this hypothesis, we have defined an upstream and intronic regulatory region of the PRNP gene. Sequencing of these regions in controls, sporadic CJD (sCJD) and variant CJD (vCJD) patients has identified three polymorphisms, all of which are more common in sCJD patients than controls. Our data suggests that polymorphisms in the regulatory region of the PRNP gene may be a risk factor for CJD.

Regulation of the cellular prion protein gene expression depends on chromatin conformation

Conversion of the normal cellular prion protein (PrPc), whose physiological function is still under investigation, to an infectious form called prion is the cause of some neurodegenerative diseases. Therefore, the elucidation of PrPc gene regulation is important both to define a strategy to control the infection and to better understand PrPc function. We cloned the rat PrPc gene promoter region into a luciferase reporter vector, transfected C6 and PC-12 cells, and isolated clones with stable enzyme expression. The dependence of chromatin conformation on PrPc promoter activity was evaluated using the histone deacetylase inhibitor, trichostatin A, which was able to highly increase not only promoter activity but also PrPc mRNA and protein levels. The phorbol ester (12-O-tetradecanoylphorbol-13-acetate) and cAMP poorly induced promoter activity; retinoic acid decreased it by 50%, whereas nerve growth factor and dexamethasone had no effect. When 12-O-tetradecanoylphorbol-13-acetate or cAMP but not retinoic acid was associated with trichostatin A, a potentiation of the primary effects was observed. These new data indicate that PrPc gene regulation is highly dependent on disruption of chromatin fiber assembly, which allows some ubiquitous transcription factors accession to specific DNA elements.

Cellular prion protein: on the road for functions

Cellular prion (PrPc) is a plasma membrane glycosyphosphatidylinositol-anchored protein present in neurons but also in other cell types. Protein conservation among species suggests that PrPc may have important physiological roles. Cellular and molecular approaches have established several novel features of the regulation of PrPc expression, cellular trafficking as well as its participation in copper uptake, protection against oxidative stress, cell adhesion, differentiation, signaling and cell survival. It is therefore likely that PrPc plays pleiotropic roles in neuronal and non-neuronal cells, and as such the loss of function of PrPc may be an important component of various diseases.

Isolation and functional characterisation of the promoter region of the human prion protein gene

The human prion protein gene (PRNP) encodes a 33-35 kDa cell surface protein that is highly expressed in the central nervous system and is vital to the pathogenesis of prion diseases. We have characterised the promoter region of PRNP as a first step towards defining the mechanisms regulating its expression. Sequence analysis of a 2.7 kb genomic DNA fragment containing exon I and the 5'-flanking region of PRNP, revealed a number of putative transcriptional factor binding sites, including Sp1, Ap-1, Ap-2 and a CCAAT box. Transient transfection assays in tissue culture cells with constructs consisting of the wild-type and deletion mutants of the PRNP 2.7 kb genomic fragment driving a luciferase reporter gene, demonstrate an active promoter within a 273 bp region (-148 to +125, relative to the cap site).

Sheep and goats: natural and experimental TSEs and factors influencing incidence of disease

The major factor influencing incidence of disease following challenge with transmissible spongiform encephalopathies (TSEs) in sheep is the allotype at amino acid numbers 136, 154 and 171 of the PrP protein. There are at least two groups of TSEs, one which targets the amino acid encoded at position 136 and the other which is more influenced by the amino acid at codon 171. Within these groups of TSE types, there may additionally be sub-types, as resistance to some, but not all, "136-type" TSEs can also be affected by the amino acid at codon 154. In goats, there are also PrP polymorphisms which apparently influence incubation period of TSE disease, however, this has not found to be true for cattle and BSE incidence. Sheep PrP amino acid codons 136, 154 and 171 do not explain everything about, for example, natural scrapie occurrence in sheep flocks, and attention is now turning to the flanking regions of the PrP gene looking for sequence differences in gene expression control motifs which may also have an influence on disease development. The sheep PrP gene produces two mRNAs in peripheral tissues, the result of alternative polyadenylation in the 3' untranslated region of the gene. Results from transfection assays of murine neuroblastoma cells with constructs expressing different regions of ovine PrP mRNA have revealed the presence of sequences in the 3' untranslated region that modulate protein synthesis and have therefore the potential to affect disease progression.

Epithelial and endothelial expression of the green fluorescent protein reporter gene under the control of bovine prion protein (PrP) gene regulatory sequences in transgenic mice

The expression of the cellular form of the prion protein (PrP(c)) gene is required for prion replication and neuroinvasion in transmissible spongiform encephalopathies. The identification of the cell types expressing PrP(c) is necessary to understanding how the agent replicates and spreads from peripheral sites to the central nervous system. To determine the nature of the cell types expressing PrP(c), a green fluorescent protein reporter gene was expressed in transgenic mice under the control of 6.9 kb of the bovine PrP gene regulatory sequences. It was shown that the bovine PrP gene is expressed as two populations of mRNA differing by alternative splicing of one 115-bp 5' untranslated exon in 17 different bovine tissues. The analysis of transgenic mice showed reporter gene expression in some cells that have been identified as expressing PrP, such as cerebellar Purkinje cells, lymphocytes, and keratinocytes. In addition, expression of green fluorescent protein was observed in the plexus of the enteric nervous system and in a restricted subset of cells not yet clearly identified as expressing PrP: the epithelial cells of the thymic medullary and the endothelial cells of both the mucosal capillaries of the intestine and the renal capillaries. These data provide valuable information on the distribution of PrP(c) at the cellular level and argue for roles of the epithelial and endothelial cells in the spread of infection from the periphery to the brain. Moreover, the transgenic mice described in this paper provide a model that will allow for the study of the transcriptional activity of the PrP gene promoter in response to scrapie infection.

Antibody binding defines a structure for an epitope that participates in the PrPC-->PrPSc conformational change

The X-ray crystallographic structures of the anti-Syrian hamster prion protein (SHaPrP) monoclonal Fab 3F4 alone, as well as the complex with its cognate peptide epitope (SHaPrP 104-113), have been determined to atomic resolution. The conformation of the decapeptide is an Omega-loop. There are substantial alterations in the antibody combining region upon epitope binding. The peptide binds in a U-shaped groove on the Fab surface, with the two specificity determinants, Met109 and Met112, penetrating deeply into separate hydrophobic cavities formed by the heavy and light chain complementarity-determining regions. In addition to the numerous contacts between the Fab and the peptide, two intrapeptide hydrogen bonds are observed, perhaps indicating the structure bound to the Fab exists transiently in solution. This provides the first structural information on a portion of the PrP N-terminal region observed to be flexible in the NMR studies of SHPrP 90-231, SHaPrP 29-231 and mouse PrP 23-231. Antibody characterization of the antigenic surfaces of PrPC and PrPSc identifies this flexible region as a component of the conformational rearrangement that is an essential feature of prion disease.

PrP (prion) gene expression in sheep may be modulated by alternative polyadenylation of its messenger RNA

Scrapie-associated fibrils and their major protein component, PrP or prion protein, accumulate in the brains and some other tissues of all species affected by transmissible spongiform encephalopathies or prion diseases. To investigate the role of PrP gene expression in the hosts of these diseases, we have analysed some characteristics of PrP gene RNA transcripts in sheep and cattle tissues and made comparisons with PrP RNA transcripts in human and mouse tissues. Two PrP messenger RNAs of 4.6 kb and 2.1 kb, the result of alternative polyadenylation, were found first in sheep peripheral tissues and also occurred at low levels in sheep brain and bovine tissues, but not in human and mouse tissues. Our results from transfection assays of murine neuroblastoma cells with constructs expressing different regions of ovine PrP messenger RNA revealed the presence of sequences in the 3' untranslated region of the gene that modulate protein synthesis.

Alternative usage of exon 1 of bovine PrP mRNA

Here we report two types of bovine prion protein (PrP) mRNA that possessed different lengths of the 5'-untranslated region and were expressed in various bovine tissues. The two mRNA species were transcribed from identical positions but differed in the usage of the splice site for exon 1/intron. One mRNA possessed exon 1 consisting of 53 nucleotides and the other possessed exon 1 consisting of 168 nucleotides. Usage of exons 2 and 3 was identical for the two mRNA species. The two mRNA species were detected in all but spleen tissue; the mRNA possessing 168-nt exon 1 was not detected in bovine spleen. This is the first report on the tissue-specific alternative splicing of PrPc mRNA in any other species. Only a low level of PrPc appeared to be present in bovine spleen. These results suggested the possibility that the mRNA possessing 53-nt exon 1 was inefficiently translated into Prp; however, in vitro translation analysis showed no marked difference in translational efficiency between the two mRNA species.