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Heterokaryon analysis of muscle differentiation: regulation of the postmitotic state

C H Clegg, S D Hauschka

    The Journal of Cell Biology
    |August 1, 1987
    PubMed

    Insights

    Skeletal muscle cells can re-enter the cell cycle if fused with mitogen-responsive cells. Diffusible factors from myocytes, however, inhibit DNA synthesis, regulating the postmitotic state.

    Area of Science:

    • Cell Biology
    • Developmental Biology
    • Muscle Physiology

    Background:

    • Skeletal muscle cells (myocytes) typically withdraw irreversibly from the cell cycle.
    • Fibroblast growth factor deprivation induces postmitotic arrest in mouse myoblasts.
    • Understanding the regulation of this postmitotic state is crucial for skeletal muscle development.

    Purpose of the Study:

    • To investigate the mechanisms regulating the postmitotic state of skeletal muscle.
    • To determine if myonuclei retain the capacity for DNA synthesis.
    • To identify factors involved in the cell cycle arrest of myocytes.

    Main Methods:

    • Polyethylene glycol-mediated fusion of post-mitotic mouse myocytes with various cell types (3T3, L cell, DD-1 myoblasts, G1 myoblasts).
    • Culturing heterokaryons in mitogen-rich medium to assess DNA synthesis and thymidine kinase expression.
    • Analyzing proliferation dominance and cell cycle progression based on fusion partners and timing of mitogen exposure.
    • Observing muscle-specific traits and receptor expression in postmitotic heterokaryons.

    Main Results:

    • Heterokaryons of myocytes and quiescent nonmyogenic cells (3T3, L cell, DD-1) initiated DNA synthesis and replicated myonuclei.
    • Heterokaryons of myocytes and G1 myoblasts failed to replicate DNA, becoming postmitotic.
    • Proliferation in (myocyte x 3T3) and (myocyte x DD-1) heterokaryons was dependent on the timing of mitogen treatment.
    • Postmitotic (myocyte x DD-1) heterokaryons lost epidermal growth factor receptors and gained muscle-specific traits.

    Conclusions:

    • DNA synthesis is not irreversibly blocked in skeletal muscle cells.
    • Myonuclei can re-enter the cell cycle and express proliferation-related functions when stimulated by mitogens.
    • Myocyte-specific factors inhibit DNA synthesis in heterokaryons, suggesting diffusible inhibitors regulate the postmitotic state of skeletal muscle.

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