Parameters that govern the regulation of immunoglobulin delta heavy-chain gene expression.
The mu and delta immunoglobulin heavy-chain genes comprise a complex transcriptional unit in which a single mRNA precursor gives rise to mu- and delta-specific transcripts. During the immature B-cell stage, posttranscriptional processing events involving alternate splicing and cleavage-polyadenylation site selection give rise to mu- but not delta-encoding transcripts. In terminally differentiated B cells, delta mRNA is not synthesized because of a transcription termination event occurring upstream of the delta-gene locus. In an attempt to gain insight into the respective contributions of alternate splicing and cleavage-polyadenylation in the control of delta mRNA synthesis, we have constructed a set of plasmids in which membrane mu (mu m)-delta intergenic sequences containing the mu m poly(A) site but differing in splicing capacity were inserted in between a VH and delta gene. The mu m-delta insertion vectors were transfected into a B lymphoma line representative of an immature stage, and proximal mu m poly(A) site usage and delta mRNA synthesis were assessed. To determine unequivocally whether the mu m-delta intergenic region can regulate termination, the insertion vectors were also transfected into a B myeloma line, and transcription through the region was measured. In immature B-cell transfectants, splicing site selection was found to have a key role in determining poly(A) site utilization and concomitant delta mRNA expression. Mature delta mRNA synthesis was blocked by an upstream cleavage-polyadenylation event only when the proximal poly(A) site was associated with appropriate splicing signals. Furthermore, in vitro transcription assays revealed that the mu m-delta intergenic region is sufficient to regulate transcription termination within a 1,2430-base-pair region containing the mu m poly(A) site in myeloma transfectants. The mu m-delta insertion vectors provide an excellent model system for studying the regulatory aspects of this transcription termination event.
Tisch
R
R
Mount Sinai Hospital Research Institute, University of Toronto, Ontario, Canada.
Kondo
N
N
Hozumi
N
N
D001402:B-Lymphocytes / Q000502:physiology*; D005786:Gene Expression Regulation; D005803:Genes, Immunoglobulin; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007138:Immunoglobulin delta-Chains / Q000235:genetics*; D007148:Immunoglobulin mu-Chains / Q000235:genetics; D007438:Introns; D011061:Poly A / Q000235:genetics; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D014158:Transcription, Genetic; D014162:Transfection
D007143:Immunoglobulin Heavy Chains; D007138:Immunoglobulin delta-Chains; D007148:Immunoglobulin mu-Chains; D012333:RNA, Messenger; D011061:Poly A