Limited number of immunoglobulin V_H regions expressed in the mutant rabbit “Alicia”

Abstract

A unique feature of rabbit Ig is the presence of VH region allotypic specificities. In normal rabbits, more than 80% of circulating immunoglobulin molecules bear the VHa allotypic specificities, al, a2 or a3; the remaining 10% to 20% of immunoglobulin molecules lack VHa allotypic specificities and are designated VHa-. A mutant rabbit designated Alicia, in contrast, has predominantly serum immunoglobulin molecules that lack the VHa allotypic specificities (Kelus and Weiss, Proc. Natl. Acad. Sci. USA 1986. 83: 4883). To study the nature and molecular complexity of VHa- molecules, we cloned and determined the nucleotide sequence of seven cDNA prepared from splenic RNA of an Alicia rabbit. Six of the clones appeared to encode VHa- molecules; the framework regions encoded by these clones were remarkably similar to each other, each having an unusual insertion of four amino acids at position 10. This insertion of four amino acids has been seen in only 2 of 54 sequenced rabbit VH genes. The similarity of the sequences of the six VHa- clones to each other and their dissimilarity to most other VH genes leads us to suggest that the VHa- molecules in Alicia rabbits are derived predominantly from one or a small number of very similar VH genes. Such preferential utilization of a small number of VH genes may explain the allelic inheritance of VH allotypes.

Internal Duplications of DH, JH, and C Region Genes Create an Unusual IgH Gene Locus in Cattle

“…Several key molecular mechanisms including V(D)J recombination and somatic hypermutation are fundamental to the Ab repertoire diversification in mammals (21)(22)(23). As compared with humans and mice, cattle are characterized by having a single functional IGHV family with a very limited number of IGHV genes (24)(25)(26)(27)(28), which is similar to rabbits (29)(30)(31) and pigs (32,33). The present understanding of the mechanisms involved in bovine Ab diversification is still based on the partial characterization of germline IGHV, IGHD, and IGHJ gene segments.…”

Preferential expansion and survival of B lymphocytes based on VH framework 1 and framework 3 expression: "positive" selection in appendix of normal and VH-mutant rabbits.

“…VH-mutant ali/ali rabbits (18) have a small deletion encompassing the VHa allotype-encoding VHI gene at the 3' end of the VH cluster (1,19). These animals develop B cells expressing upstream VH genes including VH4, VHX, and VHY that do not encode VHa allotype-defining structures (20)(21)(22). As ali/ali rabbits mature, they produce increasing proportions (10-40%) of their total serum immunoglobulin with serological properties indistinguishable from normal a2 allotype in spite of the absence of a VHJ gene (3,18,19,22).…”

Molecular bases of genetic diversity and evolution of the immunoglobulin heavy chain variable region (IGHV) gene locus in leporids

“…The mutant rabbits derived from a VH1a2 parental rabbit in which a 10 Kb segment of genomic DNA containing the VH1 gene was deleted (Knight and Becker, 1990, Allegrucci et al, 1990, Ros et al 2004). In contrast to normal individuals of the a2 lineage, the young homozygous ali / ali mutant Alicia rabbits produced only trace amounts of a2 molecules and their serum contained mostly Ig resulting from rearranged genes not encoding VHa allotype-associated epitopes ( VHa negative or VHn genes) (Kelus and Weiss, 1986; Di Pietro et al, 1990; Chen et al, 1993). As the genes encoding the VHn allotypes map at least 100 Kb upstream of VH1 (Mage et al, 2006), it is intriguing that VDJ rearrangements of these appeared to be more prevalent than VDJ rearrangements of the D -proximal functional VHa positive VH4 gene in young Alicia rabbits.…”

“…Thus, the immunoglobulins of the young rabbits are produced by B-cells that utilize VHn . As the young “Alicia” rabbit ages, the proportions of B cells expressing serological a2 specificities increase (Kelus and Weiss, 1986; Di Pietro et al, 1990; Alegrucci et al, 1990; Chen et al, 1993; Pospisil et al, 1995). Analysis of nucleotide sequences of the promoter region showed that more than 80% of the VDJ rearrangements in older Alicia rabbits utilize either the functional VH4 or VH7 genes localized upstream of VH1 .…”