Cloning and chromosomal localization of MX1 and ETS2 to chromosome 26 of the horse (Equus caballus)

Anti-Schmallenberg Virus Activities of Type I/III Interferons-Induced Mx1 GTPases from Different Mammalian Species

Mx proteins are key factors of the innate intracellular defense mechanisms that act against viruses induced by type I/III interferons. The family Peribunyaviridae includes many viruses of veterinary importance, either because infection results in clinical disease or because animals serve as reservoirs for arthropod vectors. According to the evolutionary arms race hypothesis, evolutionary pressures should have led to the selection of the most appropriate Mx1 antiviral isoforms to resist these infections. Although human, mouse, bat, rat, and cotton rat Mx isoforms have been shown to inhibit different members of the Peribunyaviridae, the possible antiviral function of the Mx isoforms from domestic animals against bunyaviral infections has, to our knowledge, never been studied. Herein, we investigated the anti-Schmallenberg virus activity of bovine, canine, equine, and porcine Mx1 proteins. We concluded that Mx1 has a strong, dose-dependent anti-Schmallenberg activity in these four mammalian species.

Equine Mx1 Restricts Influenza A Virus Replication by Targeting at Distinct Site of its Nucleoprotein

Interferon-mediated host factors myxovirus (Mx) proteins are key features in regulating influenza A virus (IAV) infections. Viral polymerases are essential for viral replication. The Mx1 protein has been known to interact with viral nucleoprotein (NP) and PB2, resulting in the influence of polymerase activity and providing interspecies restriction. The equine influenza virus has evolved as an independent lineage to influenza viruses from other species. We estimated the differences in antiviral activities between human MxA (huMxA) and equine Mx1 (eqMx1) against a broad range of IAV strains. We found that huMxA has antiviral potential against IAV strains from non-human species, whereas eqMx1 could only inhibit the polymerase activity of non-equine species. Here, we demonstrated that NP is the main target of eqMx1. Subsequently, we found adaptive mutations in the NP of strains A/equine/Jilin/1/1989 (H3N8_JL89) and A/chicken/Zhejiang/DTID-ZJU01/2013 (H7N9_ZJ13) that confer eqMx1 resistance and sensitivity respectively. A substantial reduction in Mx1 resistance was observed for the two mutations G34S and H52N in H3N8_JL89 NP. Thus, eqMx1 is an important dynamic force in IAV nucleoprotein evolution. We, therefore, suggest that the amino acids responsible for Mx1 resistance should be regarded as a robust indicator for the pandemic potential of lately evolving IAVs.

Anti-Influenza A Virus Activities of Type I/III Interferons-Induced Mx1 GTPases from Different Mammalian Species

Type I/III interferons provide powerful and universal innate intracellular defense mechanisms against viruses. Among the antiviral effectors induced, Mx proteins of some species appear as key components of defense against influenza A viruses. It is expected that such an antiviral protein must display a platform dedicated to the recognition of said viruses. In an attempt to identify such platform in human MxA, an evolution-guided approach capitalizing on the antagonistic arms race between MxA and its viral targets and the genomic signature it left on primate genomes revealed that the surface-exposed so-called "loop L4", which protrudes from the compact structure of the MxA stalk, is a hotspot of recurrent positive selection. Since MxA is archetypic of Mx1 proteins in general, we reasoned that the L4 loop also functions as a recognition platform for influenza viruses in the Mx1 proteins of other species that had been exposed to the virus for ever. In this study, the anti-influenza activity of 5 distinct mammalian Mx1 proteins was measured by comparing the number of viral nucleoprotein-positive cells 7 h after infection in a sample of 100,000 cells expected to contain both Mx1-positive and Mx1-negative cell subpopulations. The systematic depletion (P < 0.001) of virus nucleoprotein-positive cells among equine, bubaline, porcine, and bovine Mx1-expressing cell populations compared with Mx-negative cells suggests a strong anti-influenza A activity. Looking for common anti-influenza signature elements in the sequence of these Mx proteins, we found that an aromatic residue at positions 561 or 562 in the L4 loop seems critical for the anti-influenza function and/or specificity of mammalian Mx1.

Structure of equine 2'-5'oligoadenylate synthetase (OAS) gene family and FISH mapping of OAS genes to ECA8p15-->p14 and BTA17q24-->q25

Mammalian 2'-5' oligoadenylate (2-5A) synthetases are important mediators of the antiviral activity of interferons. Both human and mouse 2-5A synthetase gene families encode four forms of enzymes: small, medium, large and ubiquitin-like. In this study, the structures of four equine OAS genes were determined using DNA sequences derived from fifteen cDNA and four BAC clones. Composition of the equine OAS gene family is more similar to that of the human OAS family than the mouse Oas family. Two OAS-containing bovine BAC clones were identified in GenBank. Both equine and bovine BAC clones were physically assigned by FISH to horse and cattle chromosomes, ECA8p15-->p14 and BTA17q24--> q25, respectively. The comparative mapping data confirm conservation of synteny between ungulates, humans and rodents.

Genomic characterization of MHC class I genes of the horse

The availability of a contig of bacterial artificial chromosome (BAC) clones spanning the equine major histocompatibility complex (MHC) made possible a detailed analysis of horse MHC class I genes. Prior to this study, only a single horse MHC class I gene had been sequenced at the genomic level. Although many ( approximately 60) MHC class I cDNA sequences had been determined and published, from this information, it was not possible to determine how many class I loci are expressed in horses or to assign individual sequences to allelic series. In this study, 15 MHC class I genes were identified in BAC subclones and fully sequenced. Because the BAC library donor horse had been bred for homozygosity at the MHC, these 15 genomic clones represent distinct MHC class I genes and pseudogenes and not alleles at a smaller number of loci. For five of the genes, cDNA sequences from these loci had previously been identified. Two additional expressed class I genes were discovered, bringing the known total of different equine MHC class I genes (loci) expressed as mRNA to seven. Expression of all seven loci was detected by reverse transcriptase-polymerase chain reaction in adult, fetal, and placental tissues. The remaining eight genes were designated as pseudogenes. This work resulted in moderate expansion of the horse MHC BAC contig length, and the remaining gap was shortened. The information contained in these equine MHC class I sequences will permit comparison of MHC class I genes expressed across different horse MHC haplotypes and between horses and other mammalian species.

Synteny and regional marker order assignment of 26 type I and microsatellite markers to the horse X- and Y-chromosomes

The hypothesis that the conservation of sex-chromosome-linked genes among placental mammals could be extended to the horse genome was tested using the UCDavis horse-mouse somatic cell hybrid (SCH) panel. By exploiting the fluorescence in-situ hybridization (FISH) technique to localize an anchor locus, X-inactivation-specific transcript (XIST) on the horse X chromosome, together with the fragmentation and translocation of the X- and Y-chromosome fragments in a somatic cell hybrid panel, we regionally assigned 13 type I and 13 type II (microsatellite) markers to the horse X- and Y-chromosomes. The synteny groups that correspond to horse X- and Y-chromosomes were identified by synteny mapping of sex-specific loci zinc finger protein X-linked (ZFX), zinc finger protein Y-linked (ZFY) and sex-determining region Y (SRY) on the SCH panel. A non-pseudoautosomal gene in the human steroid sulfatase (STS) was identified in both X- and Y-chromosome-containing clones. The regional order of the X-linked type I markers examined in this study, from Xp- to Xq-distal, was [STS-X, the voltage-gated chloride channel 4 (CLCN4)], [ZFX, delta-aminolevulinate synthase 2 (ALAS2)], XIST, coagulation factor IX (F9) and [biglycan (BGN), equine F18, glucose-6-phosphate dehydrogenase (G6PD)] (precise marker order could not be determined for genes within the same brackets). The order of the Y-linked type I markers was STS-Y, SRY and ZFY These orders are the same arrangements as reported for the human X- and Y-chromosomes, supporting the conservation of genomic organization between the human and the horse sex chromosomes. Regional ordering of X-linked type I and microsatellite markers provides the first integration of type I and type II markers in the horse X chromosome.

A comparative gene map of the horse (Equus caballus)

A comparative gene map of the horse genome composed of 127 loci was assembled based on the new assignment of 68 equine type I loci and on data published previously. PCR primers based on consensus gene sequences conserved across mammalian species were used to amplify markers for assigning 68 equine type I loci to 27 horse synteny groups established previously with a horse-mouse somatic cell hybrid panel (SCHP, UC Davis). This increased the number of coding genes mapped to the horse genome by over 2-fold and allowed refinements of the comparative mapping data available for this species. In conjunction with 57 previous assignments of type I loci to the horse genome map, these data have allowed us to confirm the assignment of 24 equine synteny groups to their respective chromosomes, to provisionally assign nine synteny groups to chromosomes, and to further refine the genetic composition established with Zoo-FISH of two horse chromosomes. The equine type I markers developed in this study provide an important resource for the future development of the horse linkage and physical genome maps.