Functional V region formation during in vitro culture of a murine immature B precursor cell line

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Abstract
B lymphocytes originate from pluripotential haematopoietic stem cells and differentiate into immunoglobulin (Ig)-producing cells. B-cell lineage differentiation is accompanied by two types of immunoglobulin gene rearrangements1–3—rearrangement of V, D and J gene segments to create a functional V gene and rearrangement of CH genes for heavy-chain switching. These results, however, have been obtained mainly by analysis of immunoglobulin gene organization of myeloma cells. Baltimore and his colleagues have established Abelson murine leukaemia virus (A-MuLV)-transformed cell lines4 and found a few lines capable of carrying out κ-gene rearrangement5 or undergoing isotype switching during in vitro culture6. To study early B-cell lineage differentiation events, we have now also established A-MuLV-transformed cell lines which are capable of differentiating from μ− to μ+and of undergoing continuing rearrangement of heavy-chain genes in culture. Analysis of immunoglobulin gene organization of these transformed cells revealed that μ− cells have already undergone DNA rearrangements involving JH segments but an additional rearrangement of JH segments is required for initiation of μ-chain synthesis. Southern blot analysis of the DNA and two-dimensional gel electrophoresis of intracytoplasmic μ-chain show that μ-chain diversity with respect to antigen specificity may be generated during this second rearrangement process. As no rearrangement of light-chain genes takes place in these cells, this implies that light-chain gene rearrangement requires some further change, or a different enzyme.