Doppel gene polymorphisms in Portuguese sheep breeds: Insights on ram fertility

No polymorphisms in the coding region of the prion-like protein gene in Thoroughbred racehorses

Prion diseases are fatal neurodegenerative diseases characterised by the accumulation of an abnormal prion protein isoform (PrP^Sc), which is converted from the normal prion protein (PrP^C). Prion diseases have been reported in an extensive number of species but not in horses up to now; therefore, horses are known to be a species resistant to prion diseases. The prion-like protein gene (PRND) is closely located downstream of the prion protein gene (PRNP) and the prion-like protein (Doppel) is a homologue with PrP. Previous studies have shown that an association between prion diseases and polymorphisms of the PRND gene is reported in the main hosts of prion diseases. Hence, we examined the genetic variations of the PRND gene in Thoroughbred horses. Interestingly, polymorphisms of the PRND gene were not detected. In addition, we conducted a comparative analysis of the amino acid sequences of the PRND gene to identify the differences between horses and other species. The amino acid sequence of the horse PRND gene showed the highest identity to that of sheep (83.7%), followed by that of goats, cattle and humans. To the best of our knowledge, this is the first genetic study of the PRND gene in horses.

Prion-like protein gene (PRND) polymorphisms associated with scrapie susceptibility in Korean native black goats

The polymorphisms of the prion protein (PRNP) gene, which encodes normal prion proteins (PrP), are known to be involved in the susceptibility of prion diseases. The prion-like protein (Doppel) gene (PRND) is the paralog of the PRNP gene and is closely located downstream of the PRNP gene. In addition, the polymorphisms of PRND correlate with disease susceptibility in several animals. We analyzed the genotype and allele frequencies of PRND polymorphisms in 246 Korean native black goats and found a total of six single nucleotide polymorphisms (SNPs) with one novel SNP, c.99C>T. We observed linkage disequilibrium (LD) within and between loci. PRND c.28T>C, c.151A>G, and c.385G>C and PRND c.65C>T and c.286G>A were in perfect LD and we have reported for the first time strong LD between PRND and PRNP or prion-related protein gene (PRNT) loci. Specifically, between the PRND c.28T>C, c.151A>G and c.385G>C and the PRNP codon 143, PRND c.99C>T and the PRNP codon 102 or PRND SNPs (c.28T>C, c.151A>G and c.385G>C) and PRNT SNP (c.321T>C). Furthermore, we confirmed that the genotype distribution of the PRNP p.His143Arg was significantly different according to that of the PRND c.28T>C (P < 0.0001). Finally, using PolyPhen-2 and PROVEAN, we predicted that two non-synonymous SNPs, c.65C>T and c.286G>A, in the PRND gene can have a detrimental effect on Doppel. To the best of our knowledge, this is the first report of genetic characteristics of the PRND gene in Korean native black goats.

Influence of the geographic distribution of prion protein gene sequence variation on patterns of chronic wasting disease spread in white-tailed deer (Odocoileus virginianus)

Managing and controlling the spread of diseases in wild animal populations is challenging, especially for social and mobile species. Effective management benefits from information about disease susceptibility, allowing limited resources to be focused on areas or populations with a higher risk of infection. Chronic wasting disease (CWD), a transmissible spongiform encephalopathy that affects cervids, was detected in Colorado in the late 1960s. CWD was detected in Illinois and Wisconsin in 2002 and has since spread through many counties. Specific nucleotide variations in the prion protein gene (PRNP) sequence have been associated with reduced susceptibility to CWD in white-tailed deer. Though genetic resistance is incomplete, the frequency of deer possessing these mutations in a population is an important factor in disease spread (i.e. herd immunity). In this study we sequenced 625 bp of the PRNP gene from a sampling of 2433 deer from Illinois and Wisconsin. In north-central Illinois where CWD was first detected, counties had a low frequency of protective haplotypes (frequency <0.20); whereas in northwestern Illinois counties, where CWD cases have only more recently been detected, the frequency of protective haplotypes (frequency >0.30) was much higher (p < 0.05). Protective haplotype frequencies varied significantly among infected and uninfected geographic areas. The frequency of protective PRNP haplotypes may contribute to population level susceptibility and may shape the way CWD has spread through Illinois. Analysis of PRNP haplotype distribution could be a useful tool to assess CWD risk and allocate resources to contain and reduce the spread of infection.

Nucleotide variants in prion-related protein (testis-specific) gene (PRNT) and effects on Chinese and Mongolian sheep phenotypes

Studies of the ovine prion-related protein (testis-specific) gene (PRNT), including studies of genetic diversity, have highlighted its potential relationship to scrapie infection and economically important ovine traits. PRNT was previously reported to be highly polymorphic in Portuguese sheep. To characterize genetic polymorphisms in this gene in Asian sheep, a direct sequencing method was used to detect polymorphic loci in PRNT in 285 individual sheep from four Chinese and one Mongolian breeds. Seven SNP variants in PRNT were identified, including three novel variants (g.93G>A, g.162G>T, and g.190A>G) and four previously reported variants (g.17 C>T, g.112G>C, g.129C>T, and g.144A>G). In the five breeds that we analyzed, the mutation frequencies of g.190A>G in Lanzhou Fat-tail sheep (LFTS) and g.129C>T in the other four varieties were high (F>0.5). Moreover, thirteen different haplotypes that had a comparable distribution in the tested breeds were also identified; 'C-G-G-C-A-G-A' occurred at the highest frequency in the five sheep breeds. Additionally, we previously explored the significance of relationships between polymorphisms in PRNP or PRND and ovine growth performance. Here, we also performed correlation analysis in all tested loci. These loci polymorphisms were significantly associated with ten different growth traits (P<0.05), except for g.93G>A. Meanwhile, in contrast to a previous study, there was no significant association between the seven SNP loci analyzed and our previously reported sheep PRND or PRNP insertion/deletion mutations. Our findings may provide new insights into polymorphic variation in ovine PRNT, which may contribute to genetic improvements in economic traits that are important for sheep breeding.

Prion protein testis specific (PRNT) gene polymorphisms and transcript level in ovine spermatozoa: Implications in freezability, fertilization and embryo production

An essential role of prion protein testis specific (PRNT) and prion protein 2 dublet (PRND) genes in the male reproductive function has been highlighted, although a deeper knowledge for the mechanisms involved is still lacking. Our goal was to determine the importance of the PRNT haplotypic variants and mRNA expression levels in ovine spermatozoa freezability and ability for fertilization and embryo developmental processes. Their association with the PRND gene polymorphisms was also analyzed. DNA from rams belonging to three Portuguese sheep breeds (n = 28) was screened by single-strand conformation polymorphism (SSCP) analysis to identify the PRNT and PRND polymorphisms. Semen collected from these rams was cryopreserved and fertility traits evaluated. The SSCP analyses revealed polymorphisms in the codons 6, 38, 43 and 48 of the PRNT coding region - respectively c.17C > T (p.Ser6Phe, which disrupts a consensus arginine-X-X serine/threonine motif); c.112G > C (p.Gly38 > Arg); and synonymous c.129T > C and c.144A > G. The polymorphisms in codons 6, 38 and 48 occur simultaneously while the one in codon 43 occurs independently. Six haplotypes were identified in the PRNT coding region, resulting in three different amino acid polymorphic variants (6S-38G-43C-48V, S6F-G38R-43C-48V and 6F-38R-43C-48V). The PRNT gene mRNA transcript level in spermatozoa was related to the identified haplotypic variants, either considering the codons 6-38-48 (P ≤ 0.0001) or the codon 43 alone (P ≤ 0.0001) or altogether (P ≤ 0.0001). An interaction between PRNT haplotypes and PRND genotypes on PRNT transcript level was also identified (P = 0.0003). Rams carrying the 17C-112G-144A PRNT haplotype had sperm with the highest post-thawed individual motility (P ≤ 0.03). Combined PRNT and PRND polymorphic variation influenced the post-thawed individual motility (P = 0.01). The male PRNT haplotypic, either considering the codons 6-38-48 and 43 altogether or the codon 43 alone, interfered (P ≤ 0.04) in embryo production rates. In conclusion, our data confirm that the PRNT gene is highly polymorphic in sheep and that the PRNT and PRND genotypes are associated. The identified polymorphisms of PRNT coding region seems to interfere on the ram spermatozoa mRNA transcript level and on male fertility, specifically in sperm freezability and ability for embryo development.

Detection of a new 20-bp insertion/deletion (indel) within sheep PRND gene using mathematical expectation (ME) method

Prion-related protein doppel gene (PRND), as an essential member of the mammalian prion gene family, is associated with the scrapie susceptibility as well as phenotype traits, so the genetic variation of the PRND has been highly concerned recently, including the single nucleiotide polymorphism (SNP) and insertion/deletion (indel). Therefore, the objective of present study was to examine the possible indel variants by mathematical expectation (ME) detection method as well as explore its associations with phenotype traits. A novel 20-bp indel was verified in 623 tested individuals representing 4 diversity sheep breeds. The results showed that 3 genotypes were detected and the minor allelic frequency were 0.008 (Lanzhou Fat-Tail sheep, LFTS), 0.084 (Small Tail Han sheep, STHS), 0.021(Tong sheep, TS) and 0.083 (Hu sheep, HS), respectively. Comparing with the traditional method of detecting samples one by one, the reaction times with ME method was decreased by 36.22% (STHS), 37.00% (HS), 68.67% (TS) and 83.33% (LFTS), respectively. Besides, this locus was significantly associated to cannon circumference index (P = 0.012) and trunk index (P = 0.037) in the Hu sheep breed. Notably, it was not concordance with the present result of DNA sequencing (GCTGTCCCTGCAGGGCTTCT) and dbSNPase of NCBI (NC_443194: g.46184887- 46184906delCTGCTGTCCCTGCAGGGCTT). Consequently, it was the first time to detect the new 20-bp indel of sheep PRND gene by ME strategy, which might provide a valuable theoretical basis for marker-assisted selection in sheep genetics and breeding.

Prion protein 2 (dublet) gene (PRND): role in ovine semen capacitation, cryopreservation and fertility

The aim of the present study was to examine the role of Doppel protein in the capacitation process and fertilising ability of both fresh and frozen–thawed (FT) spermatozoa from rams carrying different prion protein 2 (dublet) (PRND) gene polymorphisms. The detection efficacy of new anti-Doppel monoclonal antibodies and PRND mRNA quantification were also explored in ovine spermatozoa. Three different genotypes (AA, GA, GG) were identified for codon 26 of ovine PRND-c.78G>A. Using flow cytometry, a higher fluorescence was detected in fresh compared with FT sperm samples incubated with anti-Doppel primary and fluorescein isothiocyanate-conjugated secondary antibodies (P < 0.05). Capacitation was affected by semen treatment (fresh and FT) and male PRND genotype (P < 0.05). After IVF, the use of fresh semen resulted in a higher cleavage rate than the use of FT spermatozoa (P = 0.004). IVF using spermatozoa from individuals classified as carriers of the AA or GA PRND genotypes resulted in higher cleavage rates than seen using spermatozoa from GG carriers (P ≤ 0.0006). Finally, using semen from rams with the AA PRND genotype resulted in the highest Day 6 and Day 8 embryo rates (P ≤ 0.04). In conclusion, the results of the present study confirm that the identification of different PRND genotypes is important for studying the sperm capacitation process and for improving sperm cryoresistance and embryo production. Furthermore, the detection of Doppel in ejaculated ovine spermatozoa, along with its low expression after cryopreservation, strongly suggests an important physiological function of this protein in male fertility.

Prion protein gene sequence and chronic wasting disease susceptibility in white-tailed deer (Odocoileus virginianus)

The sequence of the prion protein gene (PRNP) affects susceptibility to spongiform encephalopathies, or prion diseases in many species. In white-tailed deer, both coding and non-coding single nucleotide polymorphisms have been identified in this gene that correlate to chronic wasting disease (CWD) susceptibility. Previous studies examined individual nucleotide or amino acid mutations; here we examine all nucleotide polymorphisms and their combined effects on CWD. A 626 bp region of PRNP was examined from 703 free-ranging white-tailed deer. Deer were sampled between 2002 and 2010 by hunter harvest or government culling in Illinois and Wisconsin. Fourteen variable nucleotide positions were identified (4 new and 10 previously reported). We identified 68 diplotypes comprised of 24 predicted haplotypes, with the most common diplotype occurring in 123 individuals. Diplotypes that were found exclusively among positive or negative animals were rare, each occurring in less than 1% of the deer studied. Only one haplotype (C, odds ratio 0.240) and 2 diplotypes (AC and BC, odds ratios of 0.161 and 0.108 respectively) has significant associations with CWD resistance. Each contains mutations (one synonymous nucleotide 555C/T and one nonsynonymous nucleotide 286G/A) at positions reported to be significantly associated with reduced CWD susceptibility. Results suggest that deer populations with higher frequencies of haplotype C or diplotypes AC and BC might have a reduced risk for CWD infection – while populations with lower frequencies may have higher risk for infection. Understanding the genetic basis of CWD has improved our ability to assess herd susceptibility and direct management efforts within CWD infected areas.

Ultrastructural Characterization of Fresh and Vitrified In Vitro- and In Vivo-Produced Sheep Embryos

The lower results in cryopreservation of in vitro-produced (IVP) sheep embryos, when compared to the in vivo derived, limits its use. Four groups of blastocyst (BL) were evaluated: fresh IVP (n = 3), fresh in vivo derived (n = 3), warmed IVP cryopreserved in open pulled straws (OPS, n = 3) and warmed in vivo derived cryopreserved in OPS (n = 3). Ultrastructural observation of processed fresh embryos showed a reduced number of microvilli and mitochondria in the IVP ones, as well as a lower number of mature mitochondria, that can be associated with deficient metabolism in IVP embryos, possibly involved in the lower resistance to cryopreservation. Both in vivo-derived and IVP embryos had a large number of vesicles, with light and dense content. In embryos vitrified by OPS, major changes were observed mainly in IVP embryos with small changes in grade 2 (fair) and high changes in grade 3 (bad) semithin scoring. The main changes associated with cryopreservation included disruption of cellular membranes and poor intracellular preservation, with loss of microvilli and the presence of cellular debris. In conclusion, ultrastructural evaluation of IVP blastocysts cryopreserved in OPS was herein described for the first time, reporting more severe cellular damage in these embryos when compared to those produced in vivo. This is probably associated with a lower cryotolerance that can be related to their lipid content and metabolism.

NMR solution structure and SRP54M predicted interaction of the N-terminal sequence (1-30) of the ovine Doppel protein

Prion protein (PrP(C)) biosynthesis involves a multi-step process that includes translation and post-translational modifications. While PrP has been widely investigated, for the homolog Doppel (Dpl), limited knowledge is available. In this study, we focused on a vital step of eukaryotic protein biosynthesis: targeting by the signal recognition particle (SRP). Taking the ovine Dpl (OvDpl(1-30)) peptide as a template, we studied its behavior in two different hydrophobic environments using CD and NMR spectroscopy. In both trifluoroethanol (TFE) and dihexanoyl-sn-glycero-3-phosphatidylcholine (DHPC), the OvDpl(1-30) peptide revealed to fold in an alpha-helical conformation with a well-defined central region extending from residue Cys8 until Ser22. The NMR structure was subsequently included in a computational docking complex with the conserved M-domain of SRP54 protein (SRP54M), and further compared with the N-terminal structures of mouse Dpl and bovine PrP(C) proteins. This allowed the determination of (i) common predicted N-terminal/SRP54M polar contacts (Asp331, Gln335, Glu365 and Lys432) and (ii) different N-C orientations between prion and Dpl peptides at the SRP54M hydrophobic groove, that are in agreement with each peptide electrostatic potential. Together, these findings provide new insights into the biosynthesis of prion-like proteins. Besides they also show the role of protein conformational switches in signalization toward the endoplasmic membrane, a key event of major significance in the cell cycle. They are thus of general applicability to the study of the biological function of prion-like as well as other proteins.

Inhibition of ovine in vitro fertilization by anti-Prt antibody: hypothetical model for Prt/ZP interaction

BACKGROUND

The impact of prion proteins in the rules that dictate biological reproduction is still poorly understood. Likewise, the role of prnt gene, encoding the prion-like protein testis specific (Prt), in ram reproductive physiology remains largely unknown. In this study, we assessed the effect of Prt in ovine fertilization by using an anti-Prt antibody (APPA) in fertilization medium incubated with spermatozoa and oocytes. Moreover, a computational model was constructed to infer how the results obtained could be related to a hypothetical role for Prt in sperm-zona pellucida (ZP) binding.

METHODS

Mature ovine oocytes were transferred to fertilization medium alone (control) or supplemented with APPA, or pre-immune serum (CSerum). Oocytes were inseminated with ovine spermatozoa and after 18 h, presumptive zygotes (n=142) were fixed to evaluate fertilization rates or transferred (n=374) for embryo culture until D6-7. Predicted ovine Prt tertiary structure was compared with data obtained by circular dichroism spectroscopy (CD) and a protein-protein computational docking model was estimated for a hypothetical Prt/ZP interaction.

RESULTS

The fertilizing rate was lower (P=0.006) in APPA group (46.0+/-6.79%) when compared to control (78.5+/-7.47%) and CSerum (64.5+/-6.65%) groups. In addition, the cleavage rate was higher (P<0.0001) in control (44.1+/-4.15%) than in APPA group (19.7+/-4.22%). Prt CD spectroscopy showed a 22% alpha-helical structure in 30% (m/v) aqueous trifluoroethanol (TFE) and 17% alpha in 0.6% (m/v) TFE. The predominant alpha-helical secondary structure detected correlates with the predicted three dimensional structure for ovine Prt, which was subsequently used to test Prt/ZP docking. Computational analyses predicted a favorable Prt-binding activity towards ZP domains.

CONCLUSIONS

Our data indicates that the presence of APPA reduces the number of fertilized oocytes and of cleaved embryos. Moreover, the CD analysis data reinforces the predicted ovine Prt trend towards an alpha-helical structure. Predicted protein-protein docking suggests a possible interaction between Prt and ZP, thus supporting an important role for Prt in ovine fertilization.

Is prnt a pseudogene? Identification of ram Prt in testis and ejaculated spermatozoa

A hallmark of prion diseases or transmissible spongiform encephalopaties is the conversion of the cellular prion protein (PrP(C)), expressed by the prion gene (prnp), into an abnormally folded isoform (PrP(Sc)) with amyloid-like features that causes scrapie in sheep among other diseases. prnp together with prnd (which encodes a prion-like protein designated as Doppel), and prnt (that encodes the prion protein testis specific--Prt) with sprn (shadow of prion protein gene, that encodes Shadoo or Sho) genes, constitute the "prion gene complex". Whereas a role for prnd in the proper functioning of male reproductive system has been confirmed, the function of prnt, a recently discovered prion family gene, comprises a conundrum leading to the assumption that ruminant prnt is a pseudogene with no protein expression. The main objective of the present study was to identify Prt localization in the ram reproductive system and simultaneously to elucidate if ovine prnt gene is transcribed into protein-coding RNA. Moreover, as Prt is a prnp-related protein, the amyloid propensity was also tested for ovine and caprine Prt. Recombinant Prt was used to immunize BALB/c mice, and the anti-Prt polyclonal antibody (APPA) immune response was evaluated by ELISA and Western Blot. When tested by indirect immunofluorescence, APPA showed high avidity to the ram sperm head apical ridge subdomain, before and after induced capacitation, but did not show the same behavior against goat spermatozoa, suggesting high antibody specificity against ovine-Prt. Prt was also found in the testis when assayed by immunohistochemistry during ram spermatogenesis, where spermatogonia, spermatocytes, spermatids and spermatozoa, stained positive. These observations strongly suggest ovine prnt to be a translated protein-coding gene, pointing to a role for Prt protein in the ram reproductive physiology. Besides, caprine Prt appears to exhibit a higher amyloid propensity than ovine Prt, mostly associated with its phenylalanine residue.