Linkage mapping and physical localization of the major histocompatibility complex region of the marsupial Monodelphis domestica

We used genetic linkage mapping and fluorescence in situ hybridization ( FISH) to conduct the first analysis of genic organization and chromosome localization of the major histocompatibility complex ( MHC) of a marsupial, the gray, short-tailed opossum Monodelphis domestica. Family based linkage analyses of two M. domestica MHC Class I genes ( UA1, UG) and three MHC Class II genes ( DAB, DMA, and DMB) revealed that these genes were tightly linked and positioned in the central region of linkage group 3 ( LG3). This cluster of MHC genes was physically mapped to the centromeric region of chromosome 2q by FISH using a BAC clone containing the UA1 gene. An interesting finding from the linkage analyses is that sex-specific recombination rates were virtually identical within the MHC region. This stands in stark contrast to the genome-wide situation, wherein males exhibit approximately twice as much recombination as females, and could have evolutionary implications for maintaining equality between males and females in the ability to generate haplotype diversity in this region. These analyses also showed that three non-MHC genes that flank the MHC region on human chromosome 6, myelin oligodendrocyte glycoprotein ( MOG), bone morphogenetic protein 6 ( BMP6), and prolactin ( PRL), are split among two separate linkage groups ( chromosomes) in M. domestica. Comparative analysis with eight other vertebrate species suggests strong conservation of the BMP6-PRL synteny among birds and mammals, although the BMP6 - PRL - MHC - ME1 synteny is not conserved.