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Abstract. Doppel (Dpl) is a paralogue of the mammalian Prion (PrP) protein. It is abundant in testis and, unlike PrP, it is expressed at low levels in the adult central nervous system (CNS). Besides, Dpl overexpression correlates with some prion-disease pathological features, such as ataxia and death of cerebellar neurons. Recently, ectopic expression of doppel was found in two different tumor types, specifically in glial and haematological cancers. In this study the doppel gene (PRND) mRNA and protein expression in PRT-HU2 and IPDDC-A2 astrocytoma-derived cell lines was investigated. Northern blot analysis revealed two equally abundant PRND mRNA isoforms, while real-time PCR, on nuclear and cytoplasmic RNA fractions, and cRNA in situ hybridization, on astrocytoma cells and bioptical specimens, showed a nuclear retention of PRND transcripts. Western blot analysis showed that the amount of protein expressed is low compared to the level of mRNA. Moreover deglycosylation studies indicated that Dpl undergoes unusual glycosylation processes. Immunohistochemistry experiments demonstrated that Dpl was mainly localised in the cytoplasm of the astrocytic tumor cells, and that it failed to be GPI-anchored to the cell membrane. This unusual cellular localization was also confirmed through EGFP-Dpl expression in astrocytomas; on the contrary, HeLa cells exhibited the expected Dpl membrane localization. Our findings suggest an aberrant doppel gene expression pattern, characterized by a substantial nuclear retention of the transcript, an altered post-translational modification of the protein and an unusual cytoplasmic localization. IntroductionIn 1999, the first prion-gene paralogue, doppel (PRND), was described in rodents (1,2). Subsequently, the doppel gene was confirmed in humans (3), cattle, sheep (4), and goats (5). Comparative gene expression analysis was reported on different patterns of temporal and spatial expression among prion and doppel. Thus, whereas prion protein (PrP) is widely expressed, showing the highest expression profiles within the CNS (6), doppel shows barely detectable levels in most tissue (4,7). Doppel protein (Dpl) was found highly expressed only in adult and fetal testis (8), and different groups recently proposed an involvement in male gametogenesis (9-11). Based on the structural similarities between PrP (12) and Dpl (13), a role of doppel in the development of prion neurodegenerative diseases was hypothesised (14). Specifically, when ectopically expressed in some Prnp 0/0 transgenic lines, Dpl causes Purkinje cell death and ataxia (reviewed in ref. 15). However, Dpl-induced neurodegeneration can be rescued by the introduction of a Prnp transgene (16), suggesting the possibility that the protein interacts or competes with PrP in a sort of molecular antagonism-model (17). Further studies were performed to demonstrate a direct involvement of doppel in prion-diseases in humans (7) as well as in animals (18,19). From these analyses, doppel seems not to be associated with the diseases, neither if one ...

The genomic structure of the caprine Doppel gene (PRND) was determined using the ovine sequence as a scaffold to generate PCR fragments that were aligned with a cDNA sequence obtained from testicular mRNA. The caprine gene contains two exons, 89 and >2291 bp long, separated by a 1689-bp intron. Two mRNA isoforms of 3.2 and 4.8 kb were identified in the testis, as well as the exact transcription start site by fluorescently labeled oligonucleotide extension (FLOE). Like in sheep and cattle, the open reading frame (ORF) (537 bp) lies within exon 2 and is very much conserved in sheep (99.3%) and cattle (97%). The intronic sequence is also highly conserved (95.3%) compared with sheep, with the only exception of a 47-bp insertion. The PRND ORF was sequenced in 47 healthy and 17 TSE-affected goats of the Italian Ionica breed. Seven nucleotide positions showed variation: T28C, C65T, A151G, G286A, C385G, T451C, and T528C. Five were commonly represented polymorphisms: T28C, T451C, and T528C are silent mutations at codons L10, L151, and I176, respectively, while A151G and C385G determine a T51A and L129V amino acid change, respectively. The two remaining variants, C65T and G286A, were rare, leading to the amino acid substitutions S22F and E96K, respectively. None of the polymorphisms was significantly relatable to the TSE status, and the same result was obtained by the analysis of the combined haplotypes at the five major polymorphic sites, namely, T28C, C65T, A151G, G286A, and C385G.

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