Multiple levels of analysis of an IGHG4 gene deletion

Abstract

Human immunoglobulin heavy chain constant region (IGHC) genes constitute a typical multigene family, usually comprising eleven genes on the telomere of chromosome 14 (14q32). In this region, deleted and duplicated haplotypes have been reported to exist with considerable frequency. Their origin is the result of either unequal crossing-over or looping out excision. In this paper, we report the characterization of a new type of deletion, involving the IGHG4 gene, in a subject who also carries a larger deletion of a previously described type on the second chromosome. Employment of several methods (polymerase chain reaction, standard Southern blot, pulsed field gel electrophoresis, serological techniques) to analyze these deleted haplotypes has resulted in a level of accuracy in their characterization that has not been achieved in previous cases. The site of recombination responsible for the IGHG4 deletion was restricted to a 2.5-kb region 3' of the G4 gene; this rules out any possible involvement of the S regions in the recombination process. The usefulness of the various techniques in the characterization of the deletions is also discussed, together with possible future applications in the field.

Unusual organization of the human T-cell receptor beta-chain gene complex is linked to recombination hotspots.

“…CA repeats are well spread in the genome, occurring on average at 100-kb intervals, and might be responsible for recombination in that part of the complex. The repertoire of size polymorphism within the human TCR )3 complex is similar to that described for the constant region of the immunoglobulin heavy-chain gene, where 13 large deletions and 3 large duplications have been described (3). With respect to the TCR ( complex, fragments responsible for IDRP will be of particular interest with respect to recombinogenic sequences or variable gene segments that may be present.…”

“…The critical recognition functions of those molecules are profoundly influenced by the allelic polymorphism present within a species. In addition to allelic polymorphism that arose from point mutations, structural analyses of these gene complexes have revealed size polymorphism due to the insertion or deletion of large DNA regions (3)(4)(5). The mechanism responsible for size polymorphism within immunoglobulin superfamily genes is not known.…”

Novel human immunoglobulin heavy chain constant region gene deletion haplotypes characterized by pulsed-field electrophoresis

“…These two deletions both encompass the poorly mapped AI-GP-G2 region, but we do not have any reason to believe that the two independent and unanimous estimates of Ihe distance between Al and G2 are incorrect [1,2]. The (/<'/>)/-£ haplolype characterized by others wilh PFGE gave a 200-kb band [8], A deletion in accordance wiih a NFHR evenl would generate a 205 or 225 Mhil band, depending on the original haplotype. This indicates that the Jc/.4/-fi'haplotype is the result of NEHR deletion on the 350-kb background (Fig.…”

“…From the previous study, however, we know thai Ihe deletion involves at least 14 kb [12]. This discrepancy could be due lo insertion of DNA at the event causing the deletion, or the deletion could have occurred on a 370-kb Mlu\ haploiype background, and in this case the t/cVG/ haplotype would also be due to a 25-kb deletion (Fig, 3, Table 3), In two pedigrees we have studied, the 370 kb MhA allele and the liamWX haploiype HI were eo-inherited (data not shown) and the 370 kb MhA band in the SPA family was also inherited in this fashion [8], The 370-kb A^/(/I haplotypecould thusbedue toa 20-kb insertion on an ancestral BumW\ haplotype HI. but as there have only been a limited number of .HO-kb Mlul alleles where the BamVW haplotypes have been determined, il is still possible that Ihere are 37()-kb allelesas,socialed wilh other BamWl haplotypes.…”

Molecular characterization of G2m(n+) and G2m(n−) allotypes

“…This allowed the design of the isotype-specific oligonucleotides used for colony screening and PCR. This approach was exploited by our group for molecular characterization of the genes involved in large IgHC deletions generated by unequal crossing-over (Bottaro et al 1990). The IgHC allotypes so far defined at the molecular level are due to a single or a few amino acid substitutions.…”