No abstract

In order to investigate linkage, we used serum allotypes of the two rabbit C kappa isotypes and restriction fragment length polymorphisms (RFLPs) of the genes for V kappa, C kappa, and T-cell receptor C beta. The inheritance of these genetic markers was studied through backcross and F2 matings. Southern analysis and hybridization of genomic DNA with a C kappa probe detected a 5 kb Pst I fragment linked to expression of the K2bas1 allotype and the presence of the kappa 1bbas gene and a 6.6 kb Pst I fragment linked to the expression of the K1b9 allotype, the presence of the kappa 2bas2 gene and lack of expression of the K2bas1 allotype. A V kappa probe detected a 1.3 kb Eco RI fragment linked to the presence of the kappa 1bbas gene and expression of the K2bas1 allotype. In contrast, the 9 or 14 kb Eco RI RFLP (C beta a or C beta b) detected with a Tcr beta chain probe segregated independently from C kappa allotypes and RFLPs. It has previously been found that C kappa and C beta are also unlinked in man, whereas in the mouse they are linked at a distance of approximately 8 centimorgans.

No abstract

The rabbit has two isotypic forms of the immunoglobulin kappa light chain, K1 and K2, which probably arose by duplication. In the normal rabbit, only traces of K2 light chains are produced. However, K2 levels are elevated in allotype-suppressed rabbits and in the Basilea strain which does not produce K1 because of a K1 mRNA splice site mutation. Previous cloning and sequencing showed that each isotype has its own set of J kappa genes but it was not known whether the two isotypes utilize shared or separate sets of V kappa genes. In addition, although genetic linkage of allotypes associated with the K1 and K2 genes has been demonstrated, physical linkage had not been previously demonstrated by overlapping cosmid or phage clones. We used pulsed field and transverse alternating field electrophoresis to obtain megabase maps and to estimate the size of the duplication of the rabbit kappa light chain locus. We found that the two C kappa genes are about 1 megabase apart. One explanation for the poor expression of K2, could be great physical distance from V kappa genes. However, we found that there are V kappa, J kappa and C kappa 2 genes within a approximately 105-kb fragment. Thus, physical distance of V kappa from C kappa 2 may not be the basis for poor K2 expression.