Class I genes have split from the MHC in the tammar wallaby

Abstract

Genes within the Major Histocompatibility Complex (MHC) are critical to the immune response and immunoregulation. Comparative studies have revealed that the MHC has undergone many changes throughout evolution yet in tetrapods the three different classes of MHC genes have maintained linkage, suggesting that there may be some functional advantage obtained by maintaining this clustering of MHC genes. Here we present data showing that class II and III genes, the antigen processing gene TAP2, and MHC framework genes are found together in the tammar wallaby on chromosome 2. Surprisingly class I loci were not found on chromosome 2 but were mapped to ten different locations spread across six chromosomes. This distribution of class I loci in the wallaby on nearly all autosomes is not a characteristic of all marsupials and may be a relatively recent phenomenon. It highlights the need for the inclusion of more than one marsupial species in comparative studies and raises questions regarding the functional significance of the clustering of MHC genes.

Physical map of two tammar wallaby chromosomes: A strategy for mapping in non-model mammals

“…High-density filters from the tammar wallaby BAC library (Me_KBa; Arizona Genomics Institute, Tucson, AZ, USA) were screened with pools of radioactively labelled PCR probes or overgos as described in (Deakin et al 2007). Resulting positive BACs were further screened with individual probes using dot blots of either purified BAC DNA spotted onto Hybond N+ membrane (GE Healthcare UK Ltd, Little Chalfont, Buckinghamshire, UK) or from BAC cultures spotted on Hybond N+ filters placed on LB plates containing 12 2g/ml chloramphenicol and then grown overnight at 37-C.…”

“…Although the virtual map will be a great aid to genome assembly, it is important to note that it can only act as a guide, as some genes may be missing from the opossum genome assembly that are present in the wallaby and vice versa, or there may be small-scale rear- rangements not detected by mapping just a few genes from these blocks. For example, MHC Class I genes have been assigned to three different locations on wallaby chromosome 5 (Deakin et al 2007) but no orthologues of these genes are found on opossum chromosome 4.…”

Physical mapping of the elephant X chromosome: conservation of gene order over 105 million years

“…Specificity of the overgo probes was checked by searching the elephant trace archive using BLASTN. Selected overgos were radioactively labeled with 32 P-dATP and 32 P-dCTP and hybridized to male elephant BAC library (VMRC-15) filters (BAC PAC Resources, CHORI) in pools of ten according to methods described in Deakin et al (2007). After hybridization and washes, filters were exposed to X-ray film for 1 week at −80°C.…”

Physical Mapping of Immune Genes in the Tammar Wallaby <i>(Macropus eugenii)</i>

“…Using pools of radioactively labelled overgos, the tammar wallaby BAC library (Me_KBa; Arizona Genomics Institute, Tucson, Ariz., USA) was screened following the protocols described in Deakin et al [2007]. Positive BACs were confirmed to contain the gene of interest by screening dot blots of BAC cultures with a single pair of overgo probes as described in Deakin et al [2008].…”