Patterns of gene divergence and VL promoter activity in immunoglobulin light chain clusters of the channel catfish.
The structure and genomic organization of V, J, and C segments in multiple gene clusters of the G class of catfish light (L) chain were determined to study evolutionary patterns of cluster divergence and regulatory function. The results showed that the organizational pattern is conserved; two VL segments reside in opposite transcriptional orientation to a pseudogene JL segment (psiJ), a functional JL segment, and a CL segment. Structures within the central V-psiJ-J-C regions indicate that cluster duplication occurred after the V-V-psiJ-J-C organization became fixed. VL divergence in gene clusters subsequently occurred by mechanisms that principally targeted complementarity-determining regions. The sequence of the VL-flanking regions, which contained regulatory octamer, TATA, and Pax-5 (BSAP) binding site motifs, was conserved during G cluster duplication and within VL-flanking regions in divergent lineages of bony fish. Reporter assays of catfish B cells transfected with a 742-bp VL-flanking fragment showed promoter activity in the absence of enhancer elements. The promoter's activity doubled when coupled with the catfish IgH enhancer. A 136-bp fragment containing the motifs conserved in bony fish phylogeny and located between the leader initiation codon and the initiation sites of sterile transcripts served as a minimal promoter and provided the highest B-cell activity. These constructs, however, did not act as promoters in catfish non-lymphoid cells or mammalian BJA-B B cells or fibroblasts. These results indicate that the structure and function of VL promoter regions in the regulation and tissue specificity of L-chain gene expression evolved early in phylogeny.
Jones
Julia Cay
JC
Department of Microbiology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216, USA.
Ghaffari
Seyed H
SH
Lobb
Craig J
CJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D005803:Genes, Immunoglobulin; D014644:Genetic Variation; D007059:Ictaluridae / Q000235:genetics* / Q000276:immunology*; D007127:Immunoglobulin Constant Regions / Q000235:genetics; D007133:Immunoglobulin Joining Region / Q000235:genetics; D007147:Immunoglobulin Light Chains / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family; D011401:Promoter Regions, Genetic / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
D018076:DNA, Complementary; D007127:Immunoglobulin Constant Regions; D007133:Immunoglobulin Joining Region; D007147:Immunoglobulin Light Chains; D007135:Immunoglobulin Variable Region