Katherine Belov, Gavan A. Harrison, George H. Rosenberg, Robert D. Miller, and Desmond W. Cooper
cDNAs encoding IgM heavy chain constant region (C mu) were isolated from two metatherians (marsupials) - the Australian common brushtail possum (Trichosurus vulpecula) and the South American grey short-tailed opossum (Monodelphis domestica). Analysis of the sequences suggested that they correspond to 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 acid a high degree of conservation throughout vertebrate evolution was observed. Amino acid sequence comparisons revealed a marked level of sequence similarity between the two marsupial sequences (79%), relatively high similarity between the marsupials and eutherians (63%), and lower similarities between marsupials and birds (45%), marsupials and amphibians (47%), marsupials and reptiles (45%) and marsupials and fish (37%), These data allow the incorporation of metatherians into the study of mammalian IgM evolution.