Electrophoretic comparison of Syrian and Chinese hamster species

The Père David's deer MHC class I genes show unexpected diversity patterns, with monomorphic classical genes but polymorphic nonclassical genes and pseudogenes

Père David's deer (Elaphurus davidianus) is a highly inbred species that arose from 11 founders but now comprises a population of about 3,000 individuals, making it interesting to investigate the adaptive variation of this species from the major histocompatibility complex (MHC) perspective. In this study, we isolated Elda-MHC class I loci using magnetic bead-based cDNA hybridization, and examined the molecular variations of these loci using single-strand conformation polymorphism (SSCP) and sequence analysis. We obtained seven MHC class I genes, which we designated F1, F12, G2, I7, AF, I8, and C1. Our analyses of stop codons, phylogenetic trees, amino acid conservation, and G+C content revealed that F1, F12, G2, and I7 were classical genes, AF was a nonclassical gene, and I8 and C1 were pseudogenes. Our subsequent molecular examinations showed that the diversity pattern in the Père David's deer was unusual. Most mammals have more polymorphic classical class I loci vs. the nonclassical and neutral genes. In contrast, the Père David's deer was found to be monomorphic at classical genes F1, F12, G2, and I7, dimorphic at the nonclassical AF gene, dimorphic at pseudogene I8, and tetramorphic at pseudogene C1. The adverse polymorphism patterns of Elda-I genes might provide evidence for selection too faster deplete MHC variation than drift in the bottlenecked populations, while the postbottleneck tetramorphism of the C1 pseudogene appears to be evidence of strong historical balancing selection.

Limited MHC polymorphism in the southern elephant seal: implications for MHC evolution and marine mammal population biology

Genes of the major histocompatibility complex (MHC) are highly polymorphic in most terrestrial mammal populations so far studied. Exceptions to this are typically populations that lack genome-wide diversity. Here I show that two populations of the southern elephant seal (Mirounga leonina) have low DNA restriction fragment length polymorphism at MHC loci when compared with terrestrial mammals. Limited studies on MHC polymorphism in two cetacean species suggest this is a feature of marine mammal populations in general. MHC polymorphism is thought to be maintained by balancing selection, and several types of disease-based and reproductive-based mechanisms have been proposed. For the three marine mammal species examined, the low MHC polymorphism cannot be explained by low genome-wide diversity, or by any reproductive-based selection pressure. It can, however, be explained by diminished exposure to pathogenic selection pressure compared with terrestrial mammals. Reduced exposure to pathogens would also mean that marine mammal populations may be susceptible to occasional pathogen-induced mass mortalities.

DNA variation of the mammalian major histocompatibility complex reflects genomic diversity and population history

The major histocompatibility complex (MHC) is a multigene complex of tightly linked homologous genes that encode cell surface antigens that play a key role in immune regulation and response to foreign antigens. In most species, MHC gene products display extreme antigenic polymorphism, and their variability has been interpreted to reflect an adaptive strategy for accommodating rapidly evolving infectious agents that periodically afflict natural populations. Determination of the extent of MHC variation has been limited to populations in which skin grafting is feasible or for which serological reagents have been developed. We present here a quantitative analysis of restriction fragment length polymorphism of MHC class I genes in several mammalian species (cats, rodents, humans) known to have very different levels of genetic diversity based on functional MHC assays and on allozyme surveys. When homologous class I probes were employed, a notable concordance was observed between the extent of MHC restriction fragment variation and functional MHC variation detected by skin grafts or genome-wide diversity estimated by allozyme screens. These results confirm the genetically depauperate character of the African cheetah, Acinonyx jubatus, and the Asiatic lion, Panthera leo persica; further, they support the use of class I MHC molecular reagents in estimating the extent and character of genetic diversity in natural populations.

Aminoacylase-1 isoenzymes: a comparative study

Analysis of aminoacylase-1 (ACY-1) zymograms from 21 species indicated one structural locus coding for one dimeric enzyme. Among the various strains of five laboratory mammals (Mesocricetus auratus, Cricetulus griseus, Mus musculus, Rattus norvegicus, Cavia porcellus) only in Mus musculus-strains genetic variability was found. Crosses segregating for ACY-1b/ACY-1c reveal a three-banded banding pattern typical for the heterozygous state of a dimeric enzyme. Electrophoretic comparisons of all species studied indicate a high degree of phylogenetic variability at this locus.

Screening of guinea pig strains for electrophoretic isoenzyme polymorphisms

Seven strains of guinea pig (Cavia porcellus) with different degrees of inbreeding were investigated for genetic variability by starch gel electrophoresis. Variants for six out of 31 loci (Gpd-1, Aat-1, Ak-2, Pgm-1, Ada and Gpi) are reported. The data suggest that the strains all come from a small founding population and therefore are genetically more homogenous than the visible characteristics imply. Differences between isoenzyme data and other genetic characters are described and possible underlying genetic mechanisms are discussed.

Genetic basis for species vulnerability in the cheetah

A population genetic survey of over 200 structural loci previously revealed that the South African cheetah (Acinonyx jubatus jubatus) has an extreme paucity of genetic variability, probably as a consequence of a severe population bottleneck in its recent past. The genetic monomorphism of the species is here extended to the major histocompatibility complex, since 14 reciprocal skin grafts between unrelated cheetahs were accepted. The apparent consequences of such genetic uniformity to the species include (i) great difficulty in captive breeding, (ii) a high degree of juvenile mortality in captivity and in the wild, and (iii) a high frequency of spermatozoal abnormalities in ejaculates. The species vulnerability of the cheetah was demonstrated by an epizootic of coronavirus-associated feline infectious peritonitis in an Oregon breeding colony in 1983. Exposure and spread of the coronavirus, which has a very low morbidity in domestic cats (approximately 1 percent), has decimated a heretofore productive and healthy captive population. The extreme genetic monomorphism, especially at the major histocompatibility complex, and the apparent hypersensitivity of the cheetah to a viral pathogen may be related, and provide a biological basis for understanding the adaptive significance of abundant genetic variation in outbred mammalian species.

Syrian hamsters express two monomorphic class I major histocompatibility complex molecules

The description of the Syrian hamster major histocompatibility complex (MHC), Hm-1, has progressed to the point that multiple class II alloantigens have been defined using structural and functional studies. However, no comparable success has been achieved using allotypic differences to detect class I molecules. We now report that xenoantisera raised in other species against hamster tissues have made it possible to describe class I MHC homologues in the hamster. Evidence which confirms that these molecules exist includes (1) on immunoprecipitation of radiolabeled lymphoid cell lysates, heterodimers of approximate molecular weight 47 000 and 12 000 are identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the latter representing hamster beta 2-microglobulin; (2) by direct immunoprecipitation these molecules are ubiquitously expressed on hamster tissues; (3) partial N-terminal amino acid sequence analysis reveals striking homology with class I molecules described in other species. In addition, the amino acid sequence data reveal that two class I molecules are expressed on the surfaces of hamster cells. On two-dimensional PAGE analysis, these molecules are invariant among the several strains of genetically disparate hamsters available for study. We conclude that (1) hamsters have the capacity to make class I MHC molecules, (2) at least two genetic loci are dedicated to this purpose, and (3) no allelic forms can be detected, suggesting that there is no class I polymorphism.