Major histocompatibility complex of the mole-rat

The mole-rat, Spalax ehrenbergi, is a complex subterranean rodent species whose habitat is restricted largely to the Middle East and North Africa. We typed over 50 mole-rats with mouse monoclonal and polyclonal antibodies specific for class I and class II major histocompatibility complex (Mhc) molecules. Some of these antibodies were produced against mouse Mhc molecules, others against Mhc molecules of other species. About 25% of the antibodies reacted with mole-rat lymphocytes in the cytotoxic test. Some of the serologically positive antibodies precipitated from a glycoprotein pool of mole-rat spleen cell molecules that corresponded in size with class I and class II molecules of other species. We conclude, therefore, that mole-rats, like other mammals, possess the Mhc which consists of class I and class 11 loci. We call this Mhc Spalax major histocompatibility (Smh) complex. The occurrence of a large number of different serotypes among the tested animals suggests that Smh loci are polymorphic. This Mhc polymorphism of the mole-rat contrasts with the monomorphism or oligomorphism of the Syrian hamster, a rodent with a similar ecology. Thus far no qualitative correlation could be found between Smh polymorphism and chromosome variation described in this superspecies.On leave from the Dept. of Physiology, University of Zagreb, Medical Faculty, Salata 3, Zagreb, Yugoslavia.     

Limited polymorphism at major histocompatibility complex (MHC) loci in the Swedish moose A. alces

The Swedish moose was analysed for genetic variability at major histocompatibility complex (MHC) class I and class II DQA, DQB and DRB loci using restriction fragment length polymorphism (RFLP) and single strand conformation polymorphism (SSCP) techniques. Both methods revealed limited amounts of polymorphism. Since the SSCP analysis concerned an expressed DRB gene it can be concluded that the level of functional MHC class II polymorphism, at least at the DRB locus, is low in Swedish moose. DNA fingerprinting was used to determine if the unusual pattern of low MHC variability could be explained by a low degree of genome-wide genetic diversity. Hybridizations with two minisatellite probes gave similarity indices somewhat higher than the average for other natural population, but the data suggest that the low MHC variability cannot be explained by a recent population bottleneck. However, since minisatellite sequences evolve more rapidly than MHC sequences, the low levels of MHC diversity may be attributed to a bottleneck of more ancient origin. The selection pressure for MHC variability in moose may also be reduced and we discuss the possibility that its solitary life style may reduce lateral transmission of pathogens in the population.     

Eusociality in African mole-rats: new insights from patterns of genetic relatedness in the Damaraland mole-rat (Cryptomys damarensis)

After the discovery of eusociality in the naked mole-rat, it was proposed that inbreeding and high colony relatedness in this species were the major underlying factors driving cooperative breeding in African molerats. By contrast, field and laboratory studies of the eusocial Damaraland mole-rat (Cryptomys damarensis) have raised the possibility that this species is an obligate outbreeder, although the build-up of inbreeding over several generations could still occur. Using microsatellite markers, we show that most breeding pairs in wild colonies of the Damaraland mole-rat are indeed unrelated (R = 0.02 +/- 0.04) and that mean colony relatedness (R = 0.46 +/- 0.01), determined across 15 colonies from three separate populations, is little more than half that previously identified in naked mole-rats. This finding demonstrates that normal familial levels of relatedness are sufficient for the occurrence of eusociality in mammals. Variation in the mean colony relatedness among populations provides support both for the central role played by ecological constraints in cooperative breeding and for the suggestion that inbreeding in naked mole-rats is a response to extreme constraints on dispersal. Approaches that determine the relative importance of an array of extrinsic factors in driving social evolution in African mole-rats are now required.     

Analysis of the sheep MHC using HLA class I,II, and C4 cDNA probes

Four cDNA probes for the human major histocompatibility complex (MHC) were used to investigate the sheep MHC, in conjunction with serological typing for ovine lymphocyte antigen (OLA). Lymphocytes from a family (two parents and five offspring) of Romanov sheep were subjected to genomic DNA digestion by the restriction endonuclease Eco RI, followed by gel electrophoresis. A single Southern blot representing all seven individuals was then consecutively hybridized with the class I, alpha-DC, beta-DR, and C4 probes, which were originally designed to identify HLA class I, class II (DC and DR), and C4 products, respectively. Using each of the three class I/class II probes, several bands showing DNA polymorphism were detected. The segregation of these bands in the five offspring exactly paralleled the OLA haplotype segregation established by serological typing. A further eight individuals carrying haplotypes which were phenotypically identical to those in the above-mentioned family showed bands in the corresponding positions when tested with the same three probes. Using the C4 probe, no polymorphism was detected in these fifteen individuals.Abbreviations used in this paper MHC major histocompatibility complex - OLA ovine lymphocyte antigen - kbp kilobase pair(s) - MLR mixed lymphocyte reaction - RFLP restriction fragment length polymorphism     

Syrian hamster DNA shows limited polymorphism at class I-like loci

The class I gene products of the Syrian hamster major histocompatibility complex are unique in that they lack functionally detectable polymorphism. Mouse cDNA and hamster genomic probes were used to analyze the hamster class I gene family using genomic Southern hybridization. These studies revealed that the hamster possesses a complex class I multigene family and that it shares extensive sequence homology with the corresponding mouse sequences. Unlike the mouse, however, the Syrian hamster demonstrates only limited restriction endonuclease polymorphism in these genes. These results suggest that the lack of detectable polymorphism in this species is directly related to limited DNA polymorphism. The data presented here support the hypothesis that this species has undergone an evolutionary bottleneck, i. e., that all surviving members of the species arose from a limited number of progenitors.Abbreviations used in this paper MHC major histocompatibility complex - MLR mixed lymphocyte reactions - SSC saline sodium citrate - kbp kilobase pairs - SDS sodium dodecyl sulfate     

Major histocompatibility complex of the mole-rat

The major histocompatibility complex (Mhc) is a group of loci coding for lymphocyte membrane glycoproteins that provide the context for the recognition of foreign antigens in the initial phase of the immune response. The complex contains a large number of loci, some of which are highly polymorphic. The complexity and polymorphism pose a number of questions concerning the evolution of the Mhc. In an attempt to answer some of these questions, we have begun to study the Mhc of the mole-rat, Spalax ehrenbergi, a rodent representing a complex of sibling species occupying ecologically and geographically clearly delineated regions within the borders of Israel. In an earlier publication we identified the Spalax major histocompatibility (Smh) complex serologically and biochemically. Here, we analyze the Smh by Southern blotting of DNA fragments produced by restriction enzyme digestion. The fragments were hybridized to mouse probes specific for class I, class II, and C4 genes. The analysis has revealed that the Smh complex contains as many class I genes as the mouse does and that these genes are polymorphic. The number of class II genes could not be determined with certainty, but it is probably not greater than in the mouse. Polymorphism was also detected at the loci coding for the complement component 4 (C4), which are probably closely linked to the Smh complex. The polymorphism of mole-rat class I loci contrasts with the reported monomorphism of these loci in the Syrian hamster. Since the mole-rat leads a solitary, subterranean life, as the Syrian hamster does, ecology cannot be an explanation for the lack of class I polymorphism in the latter species.On leave from the Department of Physiology, University of Zagreb Medical Faculty, Zagreb, Yugoslavia.     

Genetic analysis of three loci homologous to human G9a: evidence for linkage of a class III gene with the chicken MHC

The cDNA clones of two newly discovered genes in the class III region of the human major histocompatibility complex (MHC) were hybridized to chicken DNA. One of these cDNA clones (pG9a-4C7), which detects the single-copy human G9a (BAT8) gene, gave a repeatable restriction pattern. This heterologous cDNA clone was used to detect and map three different Pst I restriction fragment length polymorphisms among the two internationally recognized chicken reference populations. Two of the loci were unlinked to previously mapped markers, but one polymorphism cosegregated with the EaB locus in the Compton mapping population. These results provide evidence that some genes of the mammalian class III region, such as G9a, may be linked to the MHC in chickens.     

Limited polymorphism of both classes of MHC genes in four different species of the Balkan mole rat

We analyzed the restriction fragment length polymorphism of class I and class II MHC genes in DNA from 20 individuals belonging to the four different species of the complex of species of Balkan mole rats Spalax leucodon captured at four different localities in Yugoslavia. All populations were tested with four restriction enzymes and one conserved mouse probe for each of the two classes of MHC genes. The probes employed detect either limited polymorphism of class I genes or lack of polymorphic bands containing class II genes. Of the two other subterranean rodents that have been studied, four karyotype forms of the Israeli mole rat show polymorphism in both classes of MHC genes similar to the one found in all other mammals (Nieti et al. 1985), and the Syrian hamster shows limited polymorphism of class I genes and high polymorphism of class II genes (McGuire et al. 1985). Balkan mole rats belong to a new group in this respect, different from all mammals studied so far, since they apparently show limited polymorphism of both classes of MHC genes.     

MHC class II‐assortative mate choice in European badgers (Meles meles)

The major histocompatibility complex (MHC) plays a crucial role in the immune system, and in some species, it is a target by which individuals choose mates to optimize the fitness of their offspring, potentially mediated by olfactory cues. Under the genetic compatibility hypothesis, individuals are predicted to choose mates with compatible MHC alleles, to increase the fitness of their offspring. Studies of MHC‐based mate choice in wild mammals are under‐represented currently, and few investigate more than one class of MHC genes. We investigated mate choice based on the compatibility of MHC class I and II genes in a wild population of European badgers (Meles meles). We also investigated mate choice based on microsatellite‐derived pairwise relatedness, to attempt to distinguish MHC‐specific effects from genomewide effects. We found MHC‐assortative mating, based on MHC class II, but not class I genes. Parent pairs had smaller MHC class II DRB amino acid distances and smaller functional distances than expected from random pairings. When we separated the analyses into within‐group and neighbouring‐group parent pairs, only neighbouring‐group pairs showed MHC‐assortative mating, due to similarity at MHC class II loci. Our randomizations showed no evidence of genomewide‐based inbreeding, based on 35 microsatellite loci; MHC class II similarity was therefore the apparent target of mate choice. We propose that MHC‐assortative mate choice may be a local adaptation to endemic pathogens, and this assortative mate choice may have contributed to the low MHC genetic diversity in this population.     

Polymorphism of bovine major histocompatibility complex (MHC) class I genes revealed by polymerase chain reaction (PCR) and restriction enzyme analysis

The polymorphic exon 2-exon 3 region of bovine major histocompatibility complex (MHC) class I genes was amplified by polymerase chain reaction (PCR) from genomic DNA samples with characterized class I polymorphism. The primers for amplification were designed in conserved regions at the borders of exons 2 and 3, based on all available cDNA sequences. The primers should, therefore, amplify most expressed class I genes, but may also amplify non-expressed class I genes. The PCR amplified class I gene fragments of 700 bp were characterized on the basis of restriction fragment length polymorphism (RFLP). The PCR-RFLP analysis of class I genes showed that the bands in each digestion could be classified as non-polymorphic, as shared between several bovine lymphocyte antigen (BoLA)-A types, or as specific to a single BoLA-A type. The same primers were then used for amplification of class I gene fragments from eight Sahiwal animals, a breed which originated in the Indian subcontinent. These studies showed that BoLA class I PCR-RFLP could be used to study class I polymorphism in family groups.     

Close association between DNA polymorphism of bovine major histocompatibility complex class I genes and serological BoLA-A specificities

Class I genes of the bovine major histocompatibility complex (MHC) were investigated by Southern blot hybridization and by serological analysis. A large number of class I restriction fragments and an extensive polymorphism were revealed when genomic DNA samples, digested with the restriction enzyme PvuII, were hybridized with a human cDNA probe. The result indicated the presence of multiple class I genes in cattle. The extensive restriction fragment length polymorphism (RFLP) was interpreted genetically by analysing five paternal half-sib families comprising, besides the bulls, 50 offspring and their dams. No less than 21 RFLP types were distinguished in this limited sample. The class I polymorphism was also analysed using a serological test with sera corresponding to four workshop specificities (w2, w6, w10 and w16) and three locally defined specificities (SRB1, SRB2 and SRB3). There was an excellent agreement between the two typing methods since no RFLP type was associated with more than one specificity and five of the seven specificities were associated with a single RFLP type. Evidence for close genetic linkage between class I and DQ class II genes was obtained since no recombinant was found among 45 informative offspring. Linkage disequilibrium among class I, DQ class II and C4 genes was also observed. The blood group specificity M' was completely associated with the w16 class I specificity and with the haplotype I1DQ1BC4(2) in this material.     

MHC variation in birds and reptiles

The major histocompatibility complex (MHC) has been studied in a multitude of mammals by now, but much less is known about its organisation and variation in other vertebrate species. The mammalian MHC is organised as a single gene cluster, but recent studies on birds suggest that this paradigm of MHC organisation has to be supplemented. The domestic chicken thus possesses two separate gene clusters which both contain MHC class I and class II B genes, and we have shown that the ring‐necked pheasant Phasianus colchicus also has two unlinked clusters of class II B genes. We are studying the effect of the MHC on mate choice, survival and reproductive success in natural populations of birds and reptiles. For this reason, we are developing DNA techniques to determine the animals' MHC genotype. The amplification of the hypervariable exon 3 of the class I gene from songbirds and reptiles has provided us with species specific probes that can be used in Southern blot analysis. The first results indicate very extensive variation in all studied species, that is starlings Sturnus vulgaris, great reed warblers Acrocephalus arundinaceus and water pythons Liasis fuscus. The restriction fragment length polymorphism (RFLP) analysis also suggests that the number of MHC genes is significantly larger in these species than in pheasants and domestic chickens. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic drift outweighs balancing selection in shaping post-bottleneck major histocompatibility complex variation in New Zealand robins (Petroicidae)

The Chatham Island black robin, Petroica traversi, is a highly inbred, endangered passerine with extremely low levels of variation at hypervariable neutral DNA markers. In this study we investigated variation in major histocompatibility complex (MHC) class II genes in both the black robin and its nonendangered relative, the South Island robin Petroica australis australis. Previous studies have shown that Petroica have at least four expressed class II B MHC genes. In this study, the sequences of introns flanking exon 2 of these loci were characterized to design primers for peptide-binding region (PBR) sequence analysis. Intron sequences were comprised of varying numbers of repeated units, with highly conserved regions immediately flanking exon 2. Polymerase chain reaction primers designed to this region amplified three or four sequences per black robin individual, and eight to 14 sequences per South Island robin individual. MHC genes are fitness-related genes thought to be under balancing selection, so they may be more likely to retain variation in bottlenecked populations. To test this, we compared MHC variation in the black robin with artificially bottlenecked populations of South Island robin, and with their respective source populations, using restriction fragment length polymorphism analyses and DNA sequencing of the PBR. Our results indicate that the black robin is monomorphic at class II B MHC loci, while both source and bottlenecked populations of South Island robin have retained moderate levels of variation. Comparison of MHC variation with minisatellite DNA variation indicates that genetic drift outweighs balancing selection in determining MHC diversity in the bottlenecked populations. However, balancing selection appears to influence MHC diversity over evolutionary timescales, and the effects of gene conversion are evident.     

Molecular characterization and genetic mapping of class I and class II MHC genes of the domestic cat

The major histocompatibility complex (MHC) of the domestic cat has been poorly characterized to date, primarily because of numerous difficulties in the preparation of allotypic sera. We present here a comparative analysis of class I and class II genes in domestic cat populations using molecular probes of the MHC from man and mouse. The cat possesses a minimum of 20 class I loci and 5 class II genes per haploid genome. Class I genes of the domestic cat expressed limited restriction fragment length polymorphism. The average percent difference of the size of DNA fragments between individual cats was 9.0 %, a value five times lower than the value for mice, but comparable to the human DNA polymorphism level. Class I and class II genes were both genetically mapped to feline chromosome B2 using a panel of rodent x cat somatic cell hybrids. Since feline chromosome B2 is syntenically homologous to human chromosome 6 and mouse chromosome 17, these results affirm the linkage conservation of the MHC-containing linkage group in the three mammalian orders.     

Colony defense in Damaraland mole-rats, Cryptomys damarensis

I examined defense against conspecific intruders in coloniesof the Damaraland mole-rat. I introduced foreign animals tocaptive colonies and examined the effect of the sex and breedingstatus of the intruder on the sex and breeding status of thosethat defended. Intruding mole-rats were almost always attacked.Colony defense against intruders was carried out almost exclusivelyby dominant, reproductive individuals and was directed primarily toward individuals of the same sex. Nonbreeding, subordinatemole-rats participated only rarely. These results contrastsharply with colony defense in the related naked mole-rat andsuggest that investment in defense activities in Damaralandmole-rats primarily reflects repulsion of potential competitorsfor breeding status. Subordinate mole-rats may lack incentiveto participate in potentially costly defense, as they are unlikelyto gain reproductive opportunities within the colony and probablygain fitness primarily through dispersing to breed.     

Patterns of MHC selection in African mole-rats, family Bathyergidae: the effects of sociality and habitat

African mole-rats are a family of rodents exhibiting an eclectic range of social behaviour and occupying a variety of habitat types. These differences are likely to impact upon the risk of parasite transmission and virulence, with increasing sociality predicted to correspond to an increased risk of transmission. We investigate these factors by analysing the major histocompatibility complex (MHC), a set of genes responsible for encoding highly variable intermediaries of the vertebrate adaptive immune response. To this end we assessed selection at exons 2 and 3 of the MHC class II DQalpha1 gene of four African mole-rat species representing a range of social behaviours. We demonstrate that: (i) the overall pattern of selection at these exons differentiates according to the predicted function of different regions, with the presence of positive selection indicating the likely influence of host-parasite coevolution; and (ii) contrary to the often observed and predicted positive correspondence between sociality and the risk of parasite transmission, two highly social African mole-rat species in fact appear to have comparatively weak positive selection, suggesting diminished host immunity and thus a low overall risk of parasite transmission.     

Genetic polymorphism of a bovine t-complex gene (TCP1) linkage to major histocompatibility genes

Southern blot analysis of genomic cattle DNA was carried out using murine cDNA probes representing the Tcp-1 gene of the t complex. Excellent cross-hybridization was obtained, and the probes apparently hybridized to at least two bovine TCP1 genes. Two independent restriction fragment length polymorphisms, each composed of two allelic variants, were detected; the inheritance of the restriction fragment length polymorphisms was confirmed by family data. One of the restriction fragment length polymorphisms, designated TCP1B, was evidently due to a gene duplication and was revealed with any restriction enzyme used. The duplication was found in three different cattle breeds investigated. Family segregation data indicated that TCP1B is linked to major histocompatibility complex genes. The result was consistent with close linkage to the major histocompatibility complex class II DO beta gene, whereas a fairly high recombination frequency was indicated between TCP1B/DO beta and other major histocompatibility complex genes. The result assigns TCP1B to a bovine linkage group previously comprising major histocompatibility complex class I and class II genes and blood group locus M. The similarity between this linkage group and parts of mouse chromosome 17 (t-H-2) and human chromosome 6 (TCP1-HLA) is discussed.     

Polymorphism and signature of selection in the MHC class I genes of the three-spined stickleback Gasterosteus aculeatus

The role and intensity of positive selection maintaining the polymorphism of major histocompatibility complex (MHC) class I genes in the three-spined stickleback Gasterosteus aculeatus was investigated. The highly polymorphic set of MHC class I genes found was organized in a single linkage group. Between 5 and 14 sequence variants per individual were identified by single-stranded conformation polymorphism (SSCP) analysis. Segregation analysis studied in 10 three-spined stickleback families followed the expected pattern of Mendelian inheritance. The gamete fusion in three-spined stickleback thus seems to be random with respect to the MHC class I genes. The DNA sequence analyses showed that the expressed MHC class I loci are under strong selection pressure, possibly mediated by parasites. Codons that were revealed to be under positive selection are potentially important in antigen binding. MHC class I sequences did not form significant supported clusters within a phylogenetic tree. Analogous to MHC class II genes, it was not possible to assign the class I sequences to a specific locus, suggesting that the class I genes may have been generated by recent gene duplication.     

Characterization of major histocompatibility complex class I,and class II DRB loci of captive and wild Indian leopards (<Emphasis Type="Italic">Panthera pardus fusca</Emphasis>)

The major histocompatibility complex (MHC), in vertebrate animals, is a multi-genic protein complex that encodes various receptors. During a disease, MHC interacts with the antigen and triggers a cascade of adaptive immune responses to overcome a disease outbreak. The MHC is very important region from immunological point of view, but it is poorly characterized among Indian leopards. During this investigation, we examined genetic diversity for MHC class I (MHC-I) and MHC class II-DRB (MHC-II) among wild and captive Indian leopards. This study estimated a pool of 9 and 17 alleles for MHC-I and MHC-II, respectively. The wild group of individuals showed higher nucleotide diversity and amino acid polymorphism compared to the captive group. A phylogenetic comparison with other felids revealed a clustering in MHC-I and interspersed presence in MHC-II sequences. A test for selection also revealed a deviation from neutrality at MHC-II DRB loci and higher non-synonymous substitution rate (dN) among the individuals from wild group. Further, the wild individuals showed higher dN for both MHC I and II genes compared to the group that was bred under captive conditions. These findings suggest the role of micro-evolutionary forces, such as pathogen-mediated selection, to cause MHC variations among the two groups of Indian leopards, because the two groups have been bred in two different environments for a substantial period of time. Since, MHC diversity is often linked with the quality of immunological health; the results obtained from this study fill the gap of knowledge on disease predisposition among wild and captive Indian leopards.