Cloning of the complete rat immunoglobulin delta gene: evolutionary implications.

The recent discovery of a Cdelta encoding gene in artiodactyls has raised questions regarding the evolution of the gene. In the present study, we have analysed the complete rat Cdelta gene both at the cDNA and genomic levels, showing that the rat Cdelta gene is structurally similar to the corresponding mouse gene. Analysis of the rat immunoglobulin D heavy chain cDNA tail sequences, revealed two transcripts for the secreted form with varying sizes of their 3' untranslated region (UTR), resulting from usage of two different poly(A) addition signals. Furthermore, a membrane-bound form encoding transcript, possessing a long 3' UTR, was also observed. Phylogenetic analysis supports that the Cdelta gene appeared early in the evolution of vertebrates, and it was probably duplicated from the C micro gene more than 400 million years ago.