Gene conversion contributes to Ig light chain diversity in cattle
Parng, C.L.; Hansal, S.; Goldsby, R.A.; Osborne, B.A.
Journal of Immunology 157(12): 5478-5486
1996
ISSN/ISBN: 0022-1767 PMID: 8955197 Document Number: 456581
Previous studies in mice have shown that extensive gene rearrangement is the major mechanism of diversification of the primary Ig repertoire. The present study shows that cattle depart from this pattern because rearrangement in the light chain locus is sharply limited. Furthermore, in cattle, gene conversion contributes to the diversification of the primary light chain repertoire. Sequencing of germ-line and expressed V lambda genes revealed 3 important features. Firstly, the germ line contained a number of V lambda pseudogenes; 14 of the 20 germ-line genes identified and sequenced were pseudogenes, because they had >=1 of the following defects: lack of recombination signal sequences at the 3' end, stop codons within the reading frame or truncations, and/or insertions or deletions that resulted in loss of the reading frame. Secondly, V lambda cDNA from ileal Peyer's patch B cells demonstrated that the light-chain repertoire arises from only a small number of V(J) rearrangements. Even though two J genes were identified in the germ line, all of the expressed V lambda genes contained the same J segment, indicating that only a single J gene participates in rearrangement at the lambda locus. Thirdly, a significant number of departures from the germ-line sequences of rearranged V lambda were traced to donor sequences of >=1 V lambda pseudogenes. It was concluded that a limited number of rearrangements and gene conversion contribute to diversification of the primary lambda repertoire. Although indications of a role for somatic mutation in lambda diversification were found, V gene rearrangement was not a major factor.