STRUCTURAL-ANALYSIS OF THE RAT HOMOLOG OF CD1 - EVIDENCE FOR EVOLUTIONARY CONSERVATION OF THE CD1D CLASS AND WIDESPREAD TRANSCRIPTION BY RAT-CELLS

The cDNA encoding the rat homologue of CD1 was isolated and the comple te nucleotide sequence was determined. It contained an open reading fr ame of 1008 bp that was capable of encoding a polypeptide with 336 ami no acids composed of hydrophobic leader and transmembrane sequences, t hree extracellular domains, and 5' and 3' untranslated sequences. Comp arison of the amino acid sequence of rat CD1 with those of other speci es revealed that it showed the highest similarity to mouse CD1, which belongs to the CD1D class of the CD1 system and is distinct from the c lassic CD1 class including CD1a, CD1b, and CD1c expressed primarily on human thymocytes and some dendritic cells. Widespread transcription o f rat CD1 was readily detected by Northern blot analysis in nonlymphoi d organs, including the liver, kidney, and heart, as well as in lympho id organs, including the thymus, lymph node, and spleen. Intestinal ex pression was also demonstrated by the more sensitive reverse transcrip tion-PCR method. Immunoprecipitation with a rabbit anti-rat CD1 Ab sho wed that rat CD1 was expressed on the cell surface as a beta(2)-microg lobulin-associated heterodimer. Southern blot analysis of inbred rat s trains suggested that rat CD1 shows limited polymorphism and that only one CD1 gene is detectable in the F344 rat genome. These results prov ide evidence for the conservation of CD1D class through mammalian evol ution and an apparent lack of the classic CD1 class genes in rodents. Functional similarity of rodent CD1 is implied.