Recruitment of multiple alleles within the Eb recombinational hotspot in murine MHC

Mammalian meiotic recombination hot spots

Our understanding of the details of mammalian meiotic recombination has recently advanced significantly. Sperm typing technologies, linkage studies, and computational inferences from population genetic data have together provided information in unprecedented detail about the location and activity of the sites of crossing-over in mice and humans. The results show that the vast majority of meiotic recombination events are localized to narrow DNA regions (hot spots) that constitute only a small fraction of the genome. The data also suggest that the molecular basis of hot spot activity is unlikely to be strictly determined by specific DNA sequence motifs in cis. Further molecular studies are needed to understand how hot spots originate, function and evolve.

Maternal cell traffic bounds for immune modulation: tracking maternal H-2 alleles in spleens of baby mice by DNA fingerprinting

We have previously reported that the immunization of pregnant mice with T-dependent antigens successfully induced suppression of the antigen-specific plaque-forming cell (PFC) response to the relevant antigens in the offspring. This suppression was not caused by the administered antigens, the antibodies produced by the pregnant mother, or lactational transfer, but was dependent on the presence of the intact maternal T cells. It was major histocompatibility complex (MHC)-restricted manner tolerance, which continued for at least one-sixth of the murine life. Traditionally, the placenta acts as a natural barrier, not allowing the cells to pass through. However, the results presented strongly suggested that maternal T cells pass through the placenta and subsequently induce tolerance. In this present study, we attempted to substantiate the presence of maternal cells in the fetal circulation through the use of molecular techniques. We found that a highly polymorphic microsatellite sequence within the class II Eb gene of the H-2 complex is useful for the molecular detection of various H-2 alleles. DNA polymorphic analysis was used for tracking maternal H-2 alleles in the spleens of baby mice. The main procedure involved polymerase chain reaction amplification and restriction fragment length polymorphism analysis of the DNA sequence encompassing the H-2-specific microsatellite from the genomic DNA of baby mice. The results indicated that maternal T cells of immunized pregnant mice cross the placenta into the fetus, eventually inducing antigen-specific immunological tolerance in the offspring.

Typing of murine major histocompatibility complex with a microsatellite in the class II Eb gene

Two DNA-based assays were developed for identification of the H2 alleles present in the 12 standard mouse MHC haplotypes H2b, H2d, H2f, H2j, H2k, H2p, H2q, H2r, H2s, H2u, H2v and H2z. The assays utilized polymerase chain reaction (PCR) amplification of a short stretch of genomic DNA including a highly polymorphic microsatellite from the second intron of the class II Eb gene within the murine major histocompatibility complex. The H2 Eb alleles were discerned by restriction fragment length polymorphism (RFLP) and heteroduplex analyses. For RFLP analysis amplified DNAs were digested with the restriction endonuclease Fnu4HI which delineated seven of the 12 alleles. A distinct pattern was obtained for the haplotypes H2d, H2j, H2k and H2p, whereas a group specific but distinct pattern was obtained for each of the three groups H2b, H2r and H2v, H2f, H2q and H2s, H2u and H2z. Heteroduplex analysis using a pair of haplotypes at a time helped further discriminate H2q from H2f or H2s. More importantly, heteroduplexing was quite informative in delineating the identity or disparity between two given haplotypes in a single step of PCR amplification. Both the RFLP and heteroduplex analyses are extremely sensitive and simple to operate, and since the target is genomic DNA, they can be carried out using any cell or tissue type.

Molecular analysis of a recombinational hotspot adjacent to Lmp2 gene in the mouse MHC: fine location and chromatin structure

Meiotic recombinations in the proximal region of the mouse major histocompatibility complex (MHC) are clustered within certain segments of chromosome, known as hotspots. In this study, we found that one of such hotspots, previously mapped between the Pb and Ob genes, is located very close to the 3' end of the Lmp2 gene, which encodes a subunit of a proteolytic proteasome. To analyze the molecular basis of the site specificity of hotspots, we examined the structure of the chromatin around this Lmp2 hotspot and another one located in the MHC class II Eb gene, by monitoring DNase I-hypersensitive sites (DHSSs) of the chromatin. DHSSs were detected at the both hotspots in the somatic cells. In the meiotic cells, DHSS was detected within the Eb hotspot, as previously reported, but not in the Lmp2 hotspot. Thus, open structure of chromatin during meiosis, as monitored by hypersensitivity to DNase I, is not a general feature of mouse recombinational hotspots, contrasting the case of the lower eukaryote, S. cerevisiae, in which hotspots are always associated with DHSSs.

Tracking H-2 alleles in transgenic mice by RFLP and heteroduplex analysis

Transgenic mice provide valuable tools for biological research including many areas of immunology. In studies involving the major histocompatibility complex (MHC), it is often necessary to place the desired transgene in a specific H-2 (the murine MHC) environment. In this regard, the strains commonly used for the production of transgenic mice also carry well characterized H-2 alleles and provide an appropriate genetic background for MHC related experiments. In this study, a highly polymorphic microsatellite of tetranucleotide repeats from the second intron of the class II Eb gene within the H-2 complex was used in order to identify the corresponding alleles. The relevant H-2 allele(s) along with the transgene were then tracked throughout the production of a chicken ovalbumin-specific transgenic strain. The technique involved PCR-amplification of a DNA sequence encompassing the H-2 specific microsatellite followed by RFLP and heteroduplex analyses. This approach is likely to find wide application in the background checking of transgenic mice, especially in immunological research requiring a defined H-2 background.

Minisatellite mutation rate variation associated with a flanking DNA sequence polymorphism

Human minisatellite mutation in the male germline frequently involves complex interallelic gene conversion events restricted to one end of the tandem repeat array. Some alleles at minisatellite MS32 show reduced variability in human populations and are associated with a G to C transversion upstream of the array. Analysis of single sperm demonstrated a frequently profound reduction in mutation rate at alleles carrying the C variant. This mutation suppression acts in cis, but does not affect the ability of an allele to act as sequence donor during gene conversion. This mutation rate polymorphism provides strong evidence for elements near the minisatellite that regulate tandem repeat instability.