Isolation and comparison of the IgM heavy chain constant regions from Australian (Trichosurus vulpecula) and American (Monodelphis domestica) marsupials

cDNAs encoding IgM heavy chain constant region (C mu) were isolated from tw o metatherians (marsupials) - the Australian common brushtail possum (Trich osurus vulpecula) and the South American grey short-tailed opossum (Monodel phis domestica). Analysis of the sequences suggested that they correspond t o the secreted form of C mu in both species. The domain size and structure of the marsupial C mu sequences were compared with other C mu sequences aci d a high degree of conservation throughout vertebrate evolution was observe d. Amino acid sequence comparisons revealed a marked level of sequence simi larity between the two marsupial sequences (79%), relatively high similarit y between the marsupials and eutherians (63%), and lower similarities betwe en marsupials and birds (45%), marsupials and amphibians (47%), marsupials and reptiles (45%) and marsupials and fish (37%), These data allow the inco rporation of metatherians into the study of mammalian IgM evolution. (C) 19 99 Elsevier Science Ltd. All rights reserved.