Regulated progression of a cultured pre-B-cell line to the B-cell stage

Abstract

The variable (V) regions of heavy and light immunoglobulin chains are encoded by multiple germline DNA elements which are assembled into complete variable-region genes in precursor(pre-) B lymphocytes¹. The heavy-chain V region (V_H) is assembled from three separate germline DNA elements, the variable (V_H), diversity (D) and joining (J_H) segments; whereas light-chain variable regions of either the κ or λ type are assembled from two elements, the V_L and J_L. Analysis of tumour cell lines or sorted cell populations which represent early and late pre-B cells has suggested that heavy-chain assembly and expression generally precedes that of light chains^2–5; but, primarily because of the lack of appropriate model systems to study the phenomenon, the mechanism and significance of this apparently orderly differentiation process are much debated. Here we describe for the first time a transformed cell line, 300-19, which sequentially undergoes all of the immunoglobulin gene rearrangement and expression events associated with the differentiation of pre-B cells to surface immunoglobulin-positive B lymphocytes. Analysis of the in vitro differentiation of 300-19 cells provides direct evidence for distinct differentiation phases of first V_H and subsequently V_L assembly during B-cell differentiation. Furthermore, these analyses suggest that the μ heavy chain, resulting from a productive V_HDJ_H rearrangement, has both a positive and a negative regulatory role in mediating this ordered differentiation process, that is, signalling the cessation of V_H gene assembly and simultaneously signalling the onset of V_L assembly.