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Cytoplasmic processing of myosin heavy chain messenger RNA: evidence provided by using a recombinant DNA plasmid

R M Medford, R M Wydro, H T Nguyen

    Proceedings of the National Academy of Sciences of the United States of America
    |October 1, 1980
    PubMed

    Insights

    Researchers identified a novel mechanism in muscle cells where myosin heavy chain (MHC) mRNA undergoes processing. This post-transcriptional modification involves the removal of the poly(A) tail, impacting MHC protein synthesis during muscle differentiation.

    Area of Science:

    • Molecular Biology
    • Cellular Biology
    • Biochemistry

    Background:

    • Myosin heavy chain (MHC) is crucial for muscle contraction.
    • Regulation of gene expression occurs at multiple levels, including post-transcriptionally.
    • Polyadenylation of mRNA plays a significant role in mRNA stability and translation.

    Purpose of the Study:

    • To construct and characterize a recombinant DNA plasmid (pMHC25) containing rat skeletal muscle MHC gene sequences.
    • To investigate the processing of MHC mRNA during myogenic differentiation in L6E9 myotubes.
    • To explore the role of the 3' poly(A) tail in MHC mRNA regulation.

    Main Methods:

    • Construction and verification of the pMHC25 plasmid.
    • Hybrid-arrested translation to confirm MHC protein synthesis inhibition.
    • Northern blot hybridization and pMHC25-DNA-excess filter hybridization to analyze MHC mRNA populations.

    Main Results:

    • Newly synthesized MHC mRNA in differentiated L6E9 myotubes is predominantly polyadenylated (poly(A)+).
    • Accumulated MHC mRNA during differentiation is largely non-polyadenylated or has a short poly(A) tail (poly(A)- or poly(A)-short).
    • Over 90% of newly synthesized MHC mRNA possesses a long 3' poly(A) tail, while 90% of accumulated MHC mRNA lacks it.

    Conclusions:

    • A post-transcriptional event occurs in differentiated L6E9 myotubes involving the cytoplasmic processing of MHC mRNA.
    • This processing converts poly(A)+ MHC mRNA to poly(A)- or poly(A)-short MHC mRNA.
    • The poly(A) tail status of MHC mRNA is dynamically regulated during muscle differentiation.

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