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Alternative processing of H-2Dd pre-mRNAs results in membrane expression of differentially phosphorylated protein
Abstract:
Two distinct mRNA species encoding the mouse major histocompatibility antigen H-2Dd have been identified in BALB/c spleen cells as well as in cultured cell lines expressing this cell surface glycoprotein. The alternate transcripts of H-2Dd arise from either removal or inclusion of exon VII (encoding I2) during pre-mRNA processing. The relative levels of each kind of H-2Dd transcript varied considerably between different cell types, and in all cells examined both forms of alloantigen were expressed on the cell membrane. Antigen derived from both types of transcript reacted with H-2Dd-specific monoclonal antibodies, whereas only protein lacking the 13 amino acids of I2 reacted with a specific antiserum raised against a predicted exon VI/VIII fusion peptide. Those H-2Dd proteins translated from full length, but not smaller, transcripts were phosphorylated in resting and phorbol myristate acetate-stimulated BALB/c spleen cells, suggesting that the major site of in vivo phosphorylation is within the highly conserved sequence encoded by exon VII. Thus alternative splicing of pre-mRNA transcripts is a mechanism which leads to membrane expression of two forms of H-2Dd, one of which lacks a major site of phosphorylation.
Insights
Two forms of mouse major histocompatibility antigen H-2Dd mRNA are produced by alternative splicing. This process generates two distinct H-2Dd proteins, impacting phosphorylation and cell surface expression.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- The mouse major histocompatibility antigen H-2Dd is a cell surface glycoprotein crucial for immune responses.
- Understanding the molecular mechanisms regulating H-2Dd expression is essential for immunological research.
Purpose of the Study:
- To investigate the molecular basis for the existence of distinct mRNA species encoding the H-2Dd antigen.
- To characterize the structural and functional differences between H-2Dd proteins derived from alternative transcripts.
Main Methods:
- Identification and analysis of mRNA transcripts from BALB/c spleen cells and cultured cell lines.
- Utilizing H-2Dd-specific monoclonal antibodies and antisera for protein characterization.
- Investigating protein phosphorylation in resting and stimulated cells.
Main Results:
- Two distinct mRNA species for H-2Dd were identified, differing by the inclusion or exclusion of exon VII.
- Both mRNA forms result in cell membrane expression of H-2Dd alloantigens.
- Phosphorylation of H-2Dd proteins was observed only in those translated from full-length transcripts, indicating exon VII contains a major phosphorylation site.
Conclusions:
- Alternative splicing of pre-mRNA is a mechanism generating two H-2Dd protein forms.
- One H-2Dd form, lacking exon VII, is not phosphorylated at a major site.
- These findings contribute to understanding the regulation of major histocompatibility complex (MHC) molecule expression and function.