Disease relevance of Prnd

• Both develop normally and display an identical male sterility phenotype that differs from that reported for another Prnd(-/-) mouse line [1].
• When Prnd-deficient neural tissue was inoculated with scrapie prions, typical features of prion pathology including spongiosis, gliosis and PrPSc accumulation, were observed [2].
• Linked expression of Prnp and Prnd may cause several neurodegenerative disorders [3].
• Using recombinant Dpl expressed in Escherichia coli and mouse neuroblastoma cells we demonstrate that wild type (wt) Dpl, like PrP(C), adopts a predominantly alpha-helical conformation, forms intramolecular disulfide bonds, has two N-linked oligosaccharides, and is presented on the cell surface via a glycosylphosphatidylinositol anchor [4].
• Analysis of doppel protein toxicity [5].

High impact information on Prnd

• In contrast to its homologue PrP(C), initial studies suggest that Dpl is dispensable for prion disease progression and for the generation of PrP(Sc) [6].
• Dpl deficiency did not interfere with embryonic and postnatal development, but resulted in male sterility [7].
• Dpl protein was expressed at late stages of spermiogenesis, and spermatids of Dpl mutants were reduced in numbers, immobile, malformed and unable to fertilize oocytes in vitro [7].
• We conclude that Dpl regulates male fertility by controlling several aspects of male gametogenesis and sperm-egg interaction [7].
• PrP(C)-deficient mice do not exhibit major pathologies, perhaps because they express a protein termed Dpl, which shares significant biochemical and structural homology with PrP(C) [7].

Biological context of Prnd

• Removal of its ORF does not result in pathological phenotypes, but deletions extending into the upstream intron result in cerebellar degeneration, possibly because of ectopic cis-activation of the Prnd locus that encodes the PrP(C) homologue Doppel (Dpl) [8].
• Up-regulation of Prnd mRNA in two distinct lines of PrP gene ablated (Prnp(0/0)) mice, designated Rcm0 and Ngsk, is associated with death of Purkinje cells [4].
• The reverse transcription polymerase chain reaction revealed that serum deprivation did not increase Prnp/Prnd chimeric mRNAs, which in fact was translated into a small amount of Dpl in HpL3-4 cells, whereas serum deprivation induced apoptotic cell death of HpL3-4 cells [9].
• These responses are suggestive of increased oxidative stress in the brains of the Dpl-expressing Prnp(0/0) mice [10].
• Like PrP, Dpl mRNA is expressed during embryogenesis but, in contrast to PrP, it is expressed minimally in the CNS [11].

Anatomical context of Prnd

• The Prnd gene is expressed in mouse embryos; in adult mice its transcripts are present in heart, mammary gland, spleen, testes and, in contrast to Prnp, only at very low levels in the adult CNS [12].
• No detergent-insoluble PrPLP/Dpl was detectable in the central nervous system of Ngsk Prnp0/0 mice even after the onset of ataxia [13].
• After in vitro differentiation and grafting into adult brains of PrPC-deficient Prnp0/0 mice, Dpl-deficient ES cell-derived grafts contained all neural lineages analyzed, including neurons and astrocytes [2].
• CONCLUSIONS: These findings strongly suggest that ectopic PrPLP/Dpl in the absence of PrP(C) is actively involved in the glial-cell activation in the brain [14].
• A neuronal cell line that does not express either prion or doppel proteins [15].

Associations of Prnd with chemical compounds

• A cell model which was previously established from Rikn mice (PrP-/-) remains problematic because of its ectopic expression of the doppel (Dpl) which may have a neurotoxic effect [15].
• Using Triton X-114 phase partitioning to enrich for glycosylphosphatidylinositol-anchored proteins, Dpl was detected in brain samples from Rcm0 Prnp(0/0) mice but was absent in equivalent samples from wt mice and ZrchI Prnp(0/0) mice, indicating that ectopic expression of this protein may cause cerebellar pathology in Rcm0 mice [4].
• Only partial unfolding of doppel or the mutant occurs at elevated temperature, but both exhibit full and reversible unfolding in chemical denaturation with urea [16].

Physical interactions of Prnd

• The activation capacity of the related USF-2, c-Myc and HIF-2alpha proteins was lower compared to USF-1 suggesting that USF-1 is the major E-box-binding transcription factor regulating the Prnd promoter [17].

Regulatory relationships of Prnd

• Dpl is expressed in the brains of mice that do not express PrP, and Dpl is known to be toxic to neurons [18].
• Using immunoblot analyses, we further demonstrate that doppel expression activates caspase-10 as well as caspase-3, but does not activate caspase-9 [19].

Other interactions of Prnd

• These findings raise the possibility that the cells of the molecular layer express an auxiliary protein, provisionally designated protein X, which is involved in prion formation and is likely to be distinct from the protein that mediates Dpl-induced degeneration [20].
• Involvement of upstream stimulatory factor in regulation of the mouse Prnd gene coding for Doppel protein [17].
• In contrast, Tg(Dpl)ZrchI mice showed cerebellar granule and Purkinje cell loss; the age of onset of ataxia was inversely proportional to the levels of Dpl protein [21].
• To evaluate whether the two proteins caused cerebellar neurodegeneration by the same mechanism, we generated transgenic mice selectively expressing Dpl in Purkinje cells by the same L7 promoter [22].
• Lymphocytes incubated for 18 h with IL-2 and with IFNgamma overexpressed Dpl [23].

Analytical, diagnostic and therapeutic context of Prnd

• Here we demonstrate that these phenotypic attributes of wt Dpl, wt PrP(C), and PrPDelta132-121 can be accurately recapitulated by transfected mouse cerebellar granule cell cultures [24].
• However, transient expression of PrPLP/Dpl mRNA was detectable by Northern blotting in the brain of neonatal wild-type mice, showing maximal expression around 1 week after birth [25].
• Matrix-assisted laser desorption ionization mass spectrometry of a Dpl peptide revealed binding of copper (but not other metals) to the helical alphaB/B'-loop-alphaC subregion of Dpl [26].
• Sequence determination and expression of the ovine doppel-encoding gene in transgenic mice [27].
• Sequence alignments showed a very high degree of identity between the sheep and cattle Dpl cDNAs, except for a 0.4-kb stretch in the bovine 3' untranslated region and the terminal 3' end of the sequences [28].

References