Expression and Characterization of the Rabbit CD5 Gene
Davidson, Robert M.
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CDS, a 67 kDa transmembrane glycoprotein, is found on the surface of all T cells, and a subset of B cells. In mice and humans, the CD5 B cells represent a relatively small percentage of the B cell repertoire (Kipps, 1989). Our lab has shown that essentially all rabbit B cells are CD5+ (Raman and Knight, 1992), while Kotani et ale (1992) claim that rabbits are deficient in CD5+ B cells. Three messages of 1.9 kb, 2.4 kb and 3.7 kb representing the CD5 gene are seen in Northern analysis of rabbit spleen mRNA. The 1.9 kb is not seen in mRNA from rabbit thymus. Two cDNA clones representing the 2.4 kb message (CD5-2a) and the 3.7 kb message (CD5-S) were previously isolated. CD5-2a has a putative translational start site 39 bp downstream of its 5' end, and has an open reading frame of about 1.5 kb. CD5-5 was only 2.7 kb in length and identical to CD5-2a from the 5' end of CD5-5 to the translational stop site. CD5-2a is 560 bp longer than CD5-5 at the 5' end, but CD5-5 is about 900 bp longer at the 3' end. The 5' end from CD5-5 has been isolated using 5' RACE®PCR and its nucleotide sequence is identical to that of CD5-2a through the putative translational start site. In order to determine whether the messages that these clones represent, or the 1.9 kb message, are differentially expressed in B cells or T cells mRNA was isolated from B cells and T cells. A Northern blot was prepared using this mRNA and hybridized with a rabbit CD5 Transmembrane/Cytoplasmic region cDNA probe. It is clear that both the 2.4 kb message and the 3.7 kb message are present in both B cells and T cells. The 1.9 kb message is not seen in either B cells or T cells, but it is expected that future studies will show that the 1.9 kb message is found in B cells but not T cells. The rabbit CD5 germline gene was previously isolated. By hybridizing specific probes from CDS-2a and CDS-S with different restriction digests of the germline gene, at least 12 exons in the rabbit CD5 germline gene were mapped.