Rearranged and germline immunoglobulin .kappa. genes: different states of DNase I sensitivity of C.kappa. genes in immunocompetent and nonimmune cells

Abstract

The rearrangement of a variable (V) and a constant (C) gene appears to be a necessary prerequisite for immunoglobulin gene expression. Multiple different rearranged .kappa. genes were found in several mouse myelomas, although these cells produce only one type of .kappa. chain. It is of interest to understand how only one allele within a lymphoid cell becomes expressed, while the other allele remains nonfunctional (allelic exclusion). The chromatin conformation of .kappa. genes was studied by making use of the preferential digestion of potentially active genes by DNase I. The DNase I sensitivity of .kappa. genes in myeloma tumors [MOPC-41, MOPC-21, MOPC-167 and MOPC-321], in a B cell lymphoma [WEH1 279], and in liver was determined by hybridization with DNA on Southern blots. Rearranged C.kappa. genes are DNase I sensitive in myelomas in which several .kappa. genes are rearranged, regardless of whether the rearranged genes code for the .kappa. chains are synthesized by the cell. The C.kappa. gene in germline configuration is also DNase I sensitive in a B cell lymphoma; i.e., it is in the same chromatin state as the rearranged C.kappa. gene which probably codes for the .kappa. chains produced by the cell. The altered chromatin state appears to be localized: V.kappa. genes in germline context are not DNase I sensitive in myeloma or B lymphoma cells, while C.kappa. genes present in a .kappa. gene cluster on the same chromosomes are sensitive. When rearranged, the V.kappa. genes are as sensitive to DNase I as are rearranged C.kappa. genes. V.lambda. and C.lambda. genes are not DNase I sensitive in .kappa. myelomas. Thus, commitment to .kappa. gene expression is apparently correlated with a chromatin conformation which confers increased DNase I sensitivity to the DNA in the vicinity of all C.kappa. genes in the cell. Allelic exclusion does not operate on the level of chromation conformation which can be detected by altered DNase I sensitivity.