Twelve toll-like receptor (TLR) genes in the family Equidae - comparative genomics, selection and evolution.

Toll-like receptors (TLRs) represent an important part of the innate immune system. While human and murine TLRs have been intensively studied, little is known about TLRs in non-model species. The order Perissodactyla comprises a variety of free-living and domesticated species exposed to different pathogens in different habitats and is therefore suitable for analyzing the diversity and evolution of immunity-related genes. We analyzed TLR genes in the order Perissodactyla with a focus on the family Equidae. Twelve TLRs were identified by bioinformatic analyses of online genomic resources; their sequences were confirmed in equids by genomic DNA re-sequencing of a panel of nine species. The expression of TLR11 and TLR12 was confirmed in the domestic horse by cDNA sequencing. Phylogenetic reconstruction of the TLR gene family in Perissodactyla identified six sub-families. TLR4 clustered together with TLR5; the TLR1-6-10 subfamily showed a high degree of sequence identity. The average estimated evolutionary divergence of all twelve TLRs studied was 0.3% among the Equidae; the most divergent CDS were those of Equus caballus and Equus hemionus kulan (1.34%) in the TLR3, and Equus africanus somaliensis and Equus quagga antiquorum (2.1%) in the TLR1 protein. In each TLR gene, there were haplotypes shared between equid species, most extensively in TLR3 and TLR9 CDS, and TLR6 amino acid sequence. All twelve TLR genes were under strong negative overall selection. Signatures of diversifying selection in specific codon sites were detected in all TLRs except TLR8. Differences in the selection patterns between virus-sensing and non-viral TLRs were observed.

Immunity-related gene single nucleotide polymorphisms associated with Rhodococcus equi infection in foals.

In previous work, we found significant associations of horse polymorphic microsatellite and immunity-related (IR) gene markers with Rhodococcus equi infection of foals. Here, a statistically significant association between a single nucleotide polymorphism (SNP) within the interleukin 7 receptor-encoding gene (IL7R) with high R. equi burden in transtracheal aspirates was found (Fisher's F = 0.043, odds ratio: 8.00, 95% confidence interval: 1.127-56.795). Further positional and/or functional candidate genes investigated TLR2, IL13, IL17A, IL28R, TACE/ADAM 17 and GBP1, were not associated with infection in this study. SNPs analysed were found by sequencing and appropriate restriction fragment length polymorphism markers were developed. Their associations with R. equi infection were tested by genotyping thoroughbred foals from the original study. The association was confirmed by analysing genotypes composed with genes previously reported to be associated with R. equi infection in the same group.

Microsatellite markers for evaluating the diversity of the natural killer complex and major histocompatibility complex genomic regions in domestic horses.

Genotyping microsatellite markers represents a standard, relatively easy, and inexpensive method of assessing genetic diversity of complex genomic regions in various animal species, such as the major histocompatibility complex (MHC) and/or natural killer cell receptor (NKR) genes. MHC-linked microsatellite markers have been identified and some of them were used for characterizing MHC polymorphism in various species, including horses. However, most of those were MHC class II markers, while MHC class I and III sub-regions were less well covered. No tools for studying genetic diversity of NKR complex genomic regions are available in horses. Therefore, the aims of this work were to establish a panel of markers suitable for analyzing genetic diversity of the natural killer complex (NKC), and to develop additional microsatellite markers of the MHC class I and class III genomic sub-regions in horses. Nine polymorphic microsatellite loci were newly identified in the equine NKC. Along with two previously reported microsatellites flanking this region, they constituted a panel of 11 loci allowing to characterize genetic variation in this functionally important part of the horse genome. Four newly described MHC class I/III-linked markers were added to 11 known microsatellites to establish a panel of 15 MHC markers with a better coverage of the class I and class III sub-regions. Major characteristics of the two panels produced on a group of 65 horses of 13 breeds and on five Przewalski's horses showed that they do reflect genetic variation within the horse species.

Candidate gene molecular markers as tools for analyzing genetic susceptibility to morbillivirus infection in stranded Cetaceans.

Morbilliviruses, such as Cetacean morbillivirus (CeMV) or Phocine distemper virus (PDV), represent a growing threat for marine mammals on both hemispheres. Because free-ranging animal populations strongly rely on natural resistance mechanisms, innate immunity-related genes and virus cell entry receptor genes may represent key factors involved in susceptibility to CeMV in Cetaceans. Using the next generation sequencing technology, we have sequenced 11 candidate genes in two model species, Stenella coeruleoalba and Phocoena phocoena. Suitable single nucleotide polymorphism markers of potential functional importance, located in genes coding for basigin (BSG, CD147), the signaling lymphocyte activating molecule (SLAMF1), the poliovirus-related receptor-4 (NECTIN4, PVRL4), toll-like receptors 3, 7, 8 (TLR3, TLR7, TLR8), natural resistance-associated macrophage protein (SLC11A1) and natural cytotoxicity triggering receptor 1 (NCR1), were identified in each model species, along with MHC-DQB haplotypes unique for each species. This set of molecular markers represents a potentially useful tool for studying host genetic variation and susceptibility to morbillivirus infection in Cetaceans as well as for studying functionally important genetic diversity of selected Cetacean populations.