A. S. Kelus

Genetics and expression of kappa-type light chains in Basilea rabbits.

In contrast to rabbits of b4, b5, b6, and b9 allotypes whose serum immunoglobulins (Igs) are predominantly composed of kappa-type light chains, rabbits of the mutant Basilea strain have serum Igs that are largely of lambda type. We prepared several antisera that recognized a minor K2 (bas) light chain that is produced by Basilea rabbits. With these antisera we identified the K2 (bas) isotype in the serum of the original b9/b9 male rabbit whose offspring displayed the Basilea mutant phenotype. It was present in one half of his nonmutant offspring which inherited b9 from him and another b allotype from their mothers. Breeding was conducted both in Basel and at the NIH to develop and maintain colonies of mutant Basilea strain rabbits. The data obtained during colony development confirm that the trait of expression of the bas allotype maps to the same genetic region (b locus) that is known to control the allelic b allotypes b4, b5, b6 and b9. Homozygotes or heterozygotes of b4, b5 or b6 allotype (bb/bb) were mated with homozygous bbas/bbas rabbits to produce F1s, and then F2s as well as progeny of backcrosses to both homozygous parental types (bb/bb and bbas/bbas) were produced. The bas allotype segregates as an allele (or pseudoallele) at the b locus although there was a deficiency in recovery of homozygous bas offspring in both the F2 and backcross matings to bbas/bbas parental type in the NIH colony. This selective deficiency may reflect a deleterious effect on survival of homozygous bas progeny.

IS THERE A HIGH RATE OF MITOTIC RECOMBINATION BETWEEN THE LOCI ENCODING IMMUNOGLOBULIN VH AND CH REGIONS IN GONIAL CELLS

Rabbit sera from approximately 6000 offspring of matings informative for recombination at the immunoglobulin (Ig) heavy chain locus were tested with allotype antisera by double diffusion in gel. Seven recombinants were found, R1K-R7K, and in every case the recombinational event had taken place in the male parent. Two single males each fathered two recombinant offspring: R2K, R4K and R5K, R6K. Four further recombinants, reported from other laboratories as well as two new, as yet not fully documented recombinants in our laboratory, also occurred in the male parent. The recombinational events either seperated the a locus which encodes the VH region of Ig, from the loci encoding its CH region or separated a-msm from the remaining linked loci d-e-f-g. The recombination frequency is 7/6142, approximately 0.1%. Our finding suggests that the recombinations took place in mitotic divisions during spermatogenesis. This work is the first evidence of gonial crossing-over in a mammal.

Molecular analysis of recombination sites within the immunoglobulin heavy chain locus of the rabbit.

Previously, recombinations involving genes of the rabbit immunoglobulin heavy chain locus have been documented serologically. These data indicated that the sites at which the causative recombination events occurred could have been anywhere from within the VH gene cluster up to, or 3′ of, Cμ. Since these sites could not be localized further by serological methods, we attempted to do this using techniques of molecular biology. DNAs from homozygous recombinant rabbits and from the appropriate non-recombinant parental haplotypes were characterized using Southern blots hybridized with a panel of probes derived from cloned regions of the rabbit immunoglobulin heavy chain gene complex. In all three recombinants, the site was downstream of the entireVH cluster and upstream of the JHcluster within an ∼50 kilobase (kb) egion containing expanses of repetitive-sequence DNA as well as DH genes. DH-specific probes further showed that in two of the recombinants, the recombination appears to have occurred within or 5′ of DH1 and 5′ of DH2 genes; in the third it occurred 3′ of the DH2 genes but at least ∼5 kb 5′ of the JH region.

Allotypes of rabbit IgM linked to be b Locus of the kappa polypeptide chain

SummaryIt was possible to obtain antisera againstMs7, the allele of IgM marker Ms3. We showed that both allotypes, Ms3 and Ms7, although occurring specifically on IgM molecules, are linked to allelic variants of the b4 light chain (b4.1 and b4.2). Similar markers linked to b5, b6, or b9 have not yet been discovered.