Functional analogues of the VKOx1 gene in different strains of mice: evolutionary conservation but diversity based on V-J joining

Abstract

Monoclonal antibodies to the hapten phenyloxazolone were raised 7 days after immunization in mice of six strains (BALB/c, C57BL-Igha, DBA2, RF, A/J, and CE). Hybridomas were selected that produced 260 idiotype-positive antibodies, and their light chain mRNA were partially sequenced. (RF is an idiotype-negative strain, and sequencing was done without this selection.) All newly sequenced BALB/c, C57BL-Igha, DBA/2, A/J, or CE VK segments had a 100% nucleotide homology with the VKOx1 (H3) germline gene. This gene codes for one third of early BALB/c phenyloxazolone antibodies, and according to our results the same gene has a significant role in the early response of at least five strains of mice. Four RF hybridomas had identical nucleotide sequences, suggesting that they express a non-mutated nucleotide sequence of a new VK germ-line gene (VKOx2). This gene codes for a CDR1 which is two amino acids longer than the CDR1 coded by the VKOx1 gene, but otherwise the two genes are related (94.5% sequence homology). All but one of the 16 kappa chains studied had the J5 segment; this segment had the same sequence in all six strains. One RF antibody had the J4 segment the nucleotide sequence of which differs from the BALB/c J4 segment in two places. Three of the kappa chains had an extra long CDR3. Long and "normal" kappa chains were probably coded by the same pair of germ-line genes (VKOx1 and J5, or VKOx2 and J5). The length heterogeneity was probably caused by a lack of precision in VK-JK joining.