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Effect of upstream RNA processing on selection of mu S versus mu M poly(A) sites
1Laboratory of Molecular Pathology, Department of Pathology, University of Texas Southwestern Medical Center,5323 Harry Hines Boulevard, Dallas, TX 75235, USA.
Abstract:
All of the regulatory factors responsible for augmenting microseconds mRNA levels preceding the dramatic increase in secretory IgM production upon B cell activation has not been totally elucidated. Whereas previous experiments have centered on the region of the gene specifying the choice between splicing to mu M exons versus selection of the mu S poly(A) site, we have found that upstream sequences within the Cmu gene, specifically the Cmu 4 acceptor splice site together with intronic sequences between the Cmu 3++ and Cmu 4 exons, play an important role in dictating the precision or the extent of splicing to the mu M exons even under conditions in which functional polyadenylation factors should be in excess. Therefore, splicing of upstream exons can affect remotely located downstream exons. These findings suggest that regulation of differential mu S/mu M mRNA expression may involve general processing enzymes that recognize specific cis -regulatory sequences residing within the body of the mu gene and account for the unique ability of activated B cells to secrete copious amounts of IgM.
Insights
Upstream sequences in the Cmu gene influence mu M exon splicing, impacting secretory IgM production in B cells. This reveals novel regulatory mechanisms for immunoglobulin M (IgM) mRNA expression.
Area of Science:
- Immunology
- Molecular Biology
- Gene Regulation
Background:
- The precise regulatory factors controlling messenger RNA (mRNA) levels for immunoglobulin M (IgM) production during B cell activation are not fully understood.
- Previous research focused on gene regions determining the choice between mu M exons and the mu S poly(A) site for mRNA processing.
Purpose of the Study:
- To investigate the role of upstream sequences within the Cmu gene in regulating differential mu S/mu M mRNA expression.
- To elucidate the mechanisms by which B cells achieve high levels of secretory IgM production upon activation.
Main Methods:
- Analysis of specific upstream sequences, including the Cmu 4 acceptor splice site and intronic sequences between Cmu 3 and Cmu 4 exons.
- Assessment of splicing precision and extent to mu M exons under conditions of excess polyadenylation factors.
Main Results:
- Upstream sequences, specifically the Cmu 4 acceptor splice site and intervening intronic sequences, significantly impact the accuracy and extent of splicing to mu M exons.
- Splicing of upstream exons can influence the processing of distantly located downstream exons, demonstrating long-range regulatory effects.
- These findings are observed even when polyadenylation factors are abundant, suggesting a spliceosome-mediated regulatory mechanism.
Conclusions:
- Regulation of differential mu S/mu M mRNA expression involves general processing enzymes that recognize cis-regulatory sequences within the Cmu gene.
- These regulatory mechanisms are crucial for the B cell's capacity to produce large quantities of secretory IgM following activation.
- The study highlights the intricate interplay between splicing and polyadenylation in controlling immunoglobulin gene expression.