The characterization of the region 3' of the mouse IgH cluster

Abstract

During B cell differentiation, developmentally regulated immunoglobulin DNA rearrangements occur in a sequential manner, resulting in productive heavy and light chain genes. These are transcribed under the direction of tissue specific regulatory elements. My studies have examined a {dollar}\sim{dollar}50 kb segment of DNA flanking the heavy chain cluster, which promises to have an impact on the expression of the lg genes. Analysis of the region 3{dollar}\sp\prime{dollar} of the immunoglobulin cluster, ie. 3{dollar}\sp\prime{dollar} of the C{dollar}\alpha{dollar} gene, has revealed that it contains many repeated motifs, some subsets of which are simple repeats. In addition, the region is highly variable between different strains of mice.;Southern blot analysis was used to examine DNA alterations at the heavy chain locus of a variant derived from the mouse myeloma cell line MPC-11 ({dollar}\gamma{dollar}2b,{dollar}\kappa{dollar}). In this variant we discovered duplicated IgH clusters, one of which had alterations at both the expressed V region and the region 3{dollar}\sp\prime{dollar} of the C{dollar}\alpha{dollar} gene. Subsequently, we have shown that both rearrangement events are linked through an inversion event comprising the entire expressed heavy chain cluster. A possible intermediate to the inversion event is a loop of DNA in which the V region and the 3{dollar}\sp\prime\alpha{dollar} sequences are in close proximity. In addition to the MPC-11 alterations, in various other myeloma cell lines and a B-cell hybridoma, we have detected 3{dollar}\sp\prime\alpha{dollar} somatic rearrangements through the observation of novel restriction fragments. Currently, our evidence indicates that these rearrangements are not associated with the expression of a specific isotype in B cells.;A functional role to this segment is indicated by the fact that this region is differentially methylated and hypersensitive to DNase I in a developmentally specific manner. Further, in collaboration with the laboratory of Dr. L. Eckhardt, we recently mapped a second B cell specific immunoglobulin enhancer within this 50 kb region. We are currently exploring evidence for a relationship between the functional role of this region and the DNA rearrangements which we have observed.