Genomic clone for sandbar shark lambda light chain: generation of diversity in the absence of gene rearrangement.

Abstract

While the general structure of immunoglobulin chains has remained relatively unchanged throughout evolution, the organization of the genes encoding these molecules differs substantially. To understand how the rearranging immunoglobulin system arose, it is necessary to examine living representatives of the most early vertebrate phyla. Elasmobranchs, which include the sharks, skates, and rays, are the most primitive phylogenetic class of vertebrates from which immunoglobulin DNA sequences have been obtained. In the sandbar shark (Carcharhinus plumbeus), the genes are arranged in individual clusters in which a single variable (V), joining (J), and constant (C) region gene, along with upstream regulatory elements, span a distance of -4.4 kb or =z5.8 kb. We report the complete sequence of a genomic clone encoding sandbar shark A light chain. A unique rinding of our study is that the V and J genes are fused in the germ line. Three additional clones have been shown by DNA sequencing to also have fused V and J genes. The four clones have complementarity-dete'rmining regions 3 of various lengths and amino acid sequence variability similar to the products of rearranged genes. Furthermore, analysis by polymerase chain reaction technology revealed an additional 26 genomic clones demonstrating fusion of the V and J segments. Therefore, VJ fusion is the prominent organizational feature of sandbar shark immunoglobulin light chain genes. This rinding raises questions concerning the necessity of recombination to produce an antibody repertoire capable of reacting against a diverse array of antigens.The overall structure of immunoglobulins has remained relatively unchanged throughout evolution (1), and while all vertebrates possess these immune molecules (1), there are significant differences among the various vertebrate phyla in how the genes encoding these molecules are arranged in the genome (2-5). Elasmobranchs, which include the sharks, skates, and rays and whose ancestors diverged from the rest of the vertebrates >400 million years ago (6), have a unique immunoglobulin gene arrangement system in which the genes are organized into gene clusters or cassettes, the actual number of which is unknown (3, 4). For light chains, these clusters span 3-6 kb and contain single variable (V), joining (J), and constant (C) gene elements (4, 7). We report here the sequence of a complete genomic sandbar shark (Carcharhinus plumbeus) A light chain clone.* The most striking of our results is that the V and J genes are fused in register within the germ line. In addition, we demonstrate by the polymerase chain reaction (PCR) that all 31 complete genomic light chain clones we isolated possess fused V and J genes. Fusion of some immunoglobulin gene elements has been described in the germ-line heavy chain genes of the homed shark, Heterodontusfrancisci (8), and the little skate, Raja erinacea (9).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" i...

Shark Ig Light Chain Junctions Are as Diverse as in Heavy Chains

“…Thus, of Ͼ70 L chain gene clusters, only 13 carry germline-joined VJ genes. This situation is in contrast to that of sandbar shark, where the NS3 homologue, also germline joined, occurs in greater numbers (16). This suggests that, generally, germline-joined Ig is not deleterious, as the proportion fluctuates among shark species.…”

Antibody Repertoire Development in Fetal and Neonatal Piglets. II. Characterization of Heavy Chain Complementarity-Determining Region 3 Diversity in the Developing Fetus

“…Considering the limited combinatorial diversity and lack of somatic mutation in fetal piglets, our results are consistent with the views of Davies et al regarding both Ab (28) and T cell repertoires (63), in that junctional diversity in CDR3 is responsible for most VDJ diversity and perhaps Ab specificity. Interestingly, in sharks, where VDJ rearrangement does not occur and variable regions are encoded by approximately 200 tandomly arrayed VDJs that are already rearranged in the germline, Ab diversity in these elasmobranches is predominately encoded in CDR3 (64). Thus, a species with very restricted combinatorial diversity and those lacking it altogether are still able to generate a diverse Ab repertoire using CDR3 alone.…”

High variability in complementarity‐determining regions compensates for a low number of V gene families in the λ light chain locus of the platypus

“…The multiclustered organization involves individual clusters of V-J and C regions repeated up to 100 times or more [7]. In addition, the V and J genes are sometimes fused, abrogating the need for rearrangement, for example, as seen in the sandbar shark [8].…”