Eleven distinct VH gene families and additional patterns of sequence variation suggest a high degree of immunoglobulin gene complexity in a lower vertebrate, Xenopus laevis.

Abstract

Lower vertebrate species, including Xenopus laevis, exhibit restricted antibody diversity relative to higher vertebrates. We have analyzed more than 180 VH gene-containing recombinant clones from an unamplified spleen cDNA library by selective sequencing of JH and CH positive clones following iterative hybridization screening with family-specific VH probes, 11 unique families of VH genes, each associated with a unique genomic Southern blot hybridization pattern, are described and compared. Considerable variation in the number of hybridizing components detected by each probe is evident. The nucleotide sequence difference between VH families is as great as, if not more than, that reported in other systems, including representatives of the mammalian, avian, and elasmobranch lineages. Some Xenopus Ig gene families encode alternative amino acids at positions that are otherwise invariant or very rarely substituted in known Igs. Furthermore, variations in complementarity determining region sequences among members of the same gene family and high degrees of DH and JH region complexity are described, suggesting that in at least this lower vertebrate species, the diversity of expressed Ig VH genes is not restricted.

What limits affinity maturation of antibodies in Xenopus--the rate of somatic mutation or the ability to select mutants?

“…The organization of Ig genes in Xenopus closely resembles that of mammals, and there is no shortage of the elements needed for combinatorial diversity (Hsu et al, 1989;Schwager et al, 1989Schwager et al, , 1991aHaire et al, 1990). Moreover, as we confirm here (Figure 3), there is no shortage of junctional diversity (Schwager et al, 1991a (Wabl et al, 1985;Berek and Milstein, 1988;Kocks and Rajewsky, 1989).…”

“…The Xenopus D cluster has yet to be mapped and, so far, D15 is the only germline D segment, TGGTAC, to be sequenced (clone G2, Schwager et al, 1991a). However, D sequences have been deduced from a large number of cDNA clones (Schwager et al, 1988a,b;Hsu et al, 1989;Haire et al, 1990) …”

“…Genes encoding both H and L chains have been sequenced, and there is no lack of potential elements for rearrangement (Schwager et al, , 1991aHsu et al, 1989;Haire et al, 1990;Zezza et al, 1991). As in mammals (reviewed by Tonegawa, 1983), the third complementarity determining region (CDR3) is the most diverse.…”

Limited diversity of the immunoglobulin heavy chain variable domain of the emerald rockcod Trematomus bernacchii

“…The nucleotides between the codons of the invariant Cys 104 and Asp 116 were tentatively assigned to the VH, D, and JH segments, although there were some nucleotides both at 3 and 5 ends of D segments that may be considered as N-or P-region additions. Distinct D prototype segments are arbitrarily assigned as consisting of at least two members sharing at least a 4-bp stretch [37]. Four distinct putative D segments, 4 to 19 nucleotides long, were identified; D1 was found to be the most represented segment, being utilised in 61% of the clones analysed.…”

The immunoglobulin repertoire of the rainbow trout (Oncorhynchus mykiss): definition of nine Igh-V families

“…Igh-V sequences (Kabat et al 1987) and in lower vertebrate Igh-V sequences, as in the channel catfish Igh-V3 (clone NG21; Ghaffari and Lobb, 1991) and in the Xenopus Igh-V4, Igh-V6, and Igh-V7 families (Haire et al 1990). Several other residues are conserved in all trout Igh-V families,…”