TY - JOUR
T1 - Somatic hypermutation and junctional diversification at Ig heavy chain loci in the nurse shark
AU - Malecek, Karolina
AU - Brandman, Julie
AU - Brodsky, Jennie E.
AU - Ohta, Yuko
AU - Flajnik, Martin F.
AU - Hsu, Ellen
PY - 2005/12/15
Y1 - 2005/12/15
N2 - We estimate there are ∼15 IgM H chain loci in the nurse shark genome and have characterized one locus. It consists of one V, two D, and one J germline gene segments, and the constant (C) region can be distinguished from all of the others by a unique combination of restriction endonuclease sites in Cμ2. On the basis of these Cμ2 markers, 22 cDNA clones were selected from an epigonal organ cDNA library from the same individual; their C region sequences proved to be the same up to the polyadenylation site. With the identification of the corresponding germline gene segments, CDR3 from shark H chain rearrangements could be analyzed precisely, for the first time. Considerable diversity was generated by trimming and N addition at the three junctions and by varied recombination patterns of the two D gene segments. The cDNA sequences originated from independent rearrangements events, and most carried both single and contiguous substitutions. The 53 point mutations occurred with a bias for transition changes (53%), whereas the 78 tandem substitutions, mostly 2-4 bp long, do not (36%). The nature of the substitution patterns is the same as for mutants from six loci of two nurse shark L chain isotypes, showing that somatic hypermutation events are very similar at both H and L chain genes in this early vertebrate. The cis-regulatory elements targeting somatic hypermutation must have already existed in the ancestral Ig gene, before H and L chain divergence.
AB - We estimate there are ∼15 IgM H chain loci in the nurse shark genome and have characterized one locus. It consists of one V, two D, and one J germline gene segments, and the constant (C) region can be distinguished from all of the others by a unique combination of restriction endonuclease sites in Cμ2. On the basis of these Cμ2 markers, 22 cDNA clones were selected from an epigonal organ cDNA library from the same individual; their C region sequences proved to be the same up to the polyadenylation site. With the identification of the corresponding germline gene segments, CDR3 from shark H chain rearrangements could be analyzed precisely, for the first time. Considerable diversity was generated by trimming and N addition at the three junctions and by varied recombination patterns of the two D gene segments. The cDNA sequences originated from independent rearrangements events, and most carried both single and contiguous substitutions. The 53 point mutations occurred with a bias for transition changes (53%), whereas the 78 tandem substitutions, mostly 2-4 bp long, do not (36%). The nature of the substitution patterns is the same as for mutants from six loci of two nurse shark L chain isotypes, showing that somatic hypermutation events are very similar at both H and L chain genes in this early vertebrate. The cis-regulatory elements targeting somatic hypermutation must have already existed in the ancestral Ig gene, before H and L chain divergence.
UR - http://www.scopus.com/inward/record.url?scp=29144433461&partnerID=8YFLogxK
U2 - 10.4049/jimmunol.175.12.8105
DO - 10.4049/jimmunol.175.12.8105
M3 - Article
C2 - 16339548
AN - SCOPUS:29144433461
VL - 175
SP - 8105
EP - 8115
JO - Journal of Immunology
JF - Journal of Immunology
SN - 0022-1767
IS - 12
ER -