Polymorphism in the major histocompatibility complex class II genes of Peromyscus leucopus

Characterization of Peromyscus MHC class II beta sequences by ligation-anchored RT-PCR and denaturing gradient gel electrophoresis

We characterized MHC class II beta sequences in deermice (genus Peromyscus), which are amongst the most common mammals in North America. We find evidence for two different families of class II beta loci, most closely related to either the A-type or E-type loci in Mus. Population studies suggest the presence of more than one A-type locus but only one E-type locus for the species investigated.

Major histocompatibility complex (MHC) class II polymorphism and paternity in the monogamous Hypogeomys antimena, the endangered, largest endemic Malagasy rodent

Sequence variation at a major histocompatibility complex (MHC) class II gene was examined in Hypogeomys antimena, a monogamous endemic rodent of Madagascar. The study was conducted throughout its remaining geographical range (20 x 40 km) by direct sequencing and single-strand conformation polymorphism (SSCP). The objectives of the study were: (i) to investigate levels of polymorphism in the MHC complex of a highly endangered species that experienced a severe reduction in population size; and (ii) to investigate the genetic mating system by assessing the frequency of extra-pair paternity (EPP) as EPP might have important consequences to increase gene flow and, therefore, genetic variability within a population. The amplified gene segment had a very low variability (only two alleles) in H. antimena compared with other mammalian species. The alleles segregated consistently with Mendelian expectations in families. No case of EPP was found. The present data suggest no difference between the social and the genetic mating system.

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.

Genome organization of repetitive elements in the rodent, Peromyscus leucopus

To document the frequency and distribution of repetitive elements in Peromyscus leucopus, the white-footed mouse, a cosmid genomic library was examined. Two thousand thirteen randomly chosen recombinants, with an average insert size of 35 kb and representing 2.35% of the haploid genome of P. leucopus, were screened with probes representing microsatellites, tandem repeats, and transposable elements. Of the four dinucleotides, (GT)n was present in 87% of the clones, (CT)n was present in 59% of the clones, and (AT)n and (GC)n each was represented in our sample by a single clone (0.05%). (TCC)n was present in 8% of the clones. Of the tandem repeats, the 28S ribosomal probe and the (TTAGGG)n telomere probe were not represented in the library, whereas a heterochromatic fragment was present in 9% of the clones. A transposable element, mys, was estimated to occur in 4700 copies, whereas a long interspersed element (LINE) was estimated to occur in about 41,000 copies per haploid genome. LINE and mys occurred together in the same clones more frequently than expected on the basis of chance. Hybridizing the library to genomic DNA from P. leucopus, Reithrodontomys fulvescens, Mus musculus, and human produced general agreement between phylogenetic relatedness and intensity of hybridization. However, dinucleotide repeats appeared to account for a disproportionately high number of positive clones in the more distantly related taxa.

Transmembrane domain length variation in the evolution of major histocompatibility complex class I genes

The fifth exons of major histocompatibility complex (MHC) class I genes encode a transmembrane domain (TM) that is largely responsible for class I antigen cell-surface expression usually through conventional hydrophobic amino acid-membrane interactions or, less often, through phosphatidylinositol linkage. In this report we show that Peromyscus leucopus, a Cricetidae rodent, has MHC class I genes (Pele-A genes) encoding three distinct sizes of TMs. Increases in TM lengths were due to tandem duplications of sequences similar to human hypervariable minisatellite repeats and the lambda chi site. We discerned remnants of a similar duplication event in comparable rodent and primate MHC class I genes. Furthermore, several duplications and deletions appear to have occurred independently in H-2, RT1, Pele-A, and ChLA genes in near-identical positions. Accumulated data suggests that sequences in the fifth exon of MHC class I genes may, therefore, constitute a mutational or recombinational hot spot that is mediated by minisatellite- and chi-like sequences imbedded within the coding region. The MHC class I genes may thus have recruited "selfish" DNA in their evolution to encode cell surface proteins. Expression of Pele-A genes was examined by the polymerase chain reaction (PCR) using oligonucleotide primers specific for exon 4 and 5 sequences. The PCR product sizes indicated that genes encoding each TM domain length are ubiquitously transcribed.

Major histocompatibility complex class I genes of Peromyscus leucopus

Class I genes of the Peromyscus leucopus major histocompatibility complex (MhcPele) were examined by Southern blot hybridization, genomic cloning, and DNA sequencing. At least three distinct subtypes of Pele class I genes were discerned, which we have designated Pele-A, B, and C. The nucleotide sequences of exon 5-containing regions (encoding the transmembrane domain) suggested that Pele-A genes are homologs of mouse H-2K, D, L, and Q genes and that Pele-B genes correspond to mouse Tla genes. The Pele-C genes appeared similar to mouse M1 genes. The number of unique genes in each subtype cloned from an individual P. leucopus were 20 for Pele-A, 13 for Pele-B, and 2 for Pele-C. Three genomic clones showed cross-hybridization to both Pele-A and Pele-B gene-specific probes. Six genomic clones remained unclassified as they did not cross-hybridize to exon 5-containing probes from Pele-A, B, or C genes. The homology between the transmembrane domains of Pele class I gene subtypes was found to be similar to that observed between the transmembrane domains of H-2 subtypes (or groups). Interspecific similarity of exon 5 was found to be 81%-88% between Pele class I genes and their H-2 counterparts.