The Journal of Neuroscience, February 1, 2000, 20(3):919-928
Local Control of Acetylcholinesterase Gene Expression in
Multinucleated Skeletal Muscle Fibers: Individual Nuclei Respond to
Signals from the Overlying Plasma Membrane
Susana G.
Rossi,
Ana E.
Vazquez, and
Richard L.
Rotundo
Department of Cell Biology and Anatomy, University of Miami School
of Medicine, Miami, Florida 33136
Nuclei in multinucleated skeletal muscle fibers are capable of
expressing different sets of muscle-specific genes depending on their
locations within the fiber. Here we test the hypothesis that each
nucleus can behave autonomously and responds to signals generated
locally on the plasma membrane. We used acetylcholinesterase (AChE) as
a marker because its transcripts and protein are concentrated at the
neuromuscular and myotendenous junctions. First, we show that
tetrodotoxin (TTX) reversibly suppresses accumulation of cell surface
AChE clusters, whereas veratridine or scorpion venom (ScVn)
increase them. AChE mRNA levels are also regulated by membrane depolarization. We then designed chambered cultures that allow application of sodium channel agonists or antagonists to restricted regions of the myotube surface. When a segment of myotube is exposed to
TTX, AChE cluster formation is suppressed only on that region. Conversely, ScVn increases AChE cluster formation only where in contact
with the muscle surface. Likewise, both the synthesis and secretion of
AChE are shown to be locally regulated. Moreover, using in
situ hybridization, we show that the perinuclear accumulation of AChE transcripts also depends on signals that each nucleus receives
locally. Thus AChE can be up- and downregulated in adjacent regions of
the same myotubes. These results indicate that individual nuclei are
responding to locally generated signals for cues regulating gene expression.
Key words:
neuromuscular junction; skeletal muscle; gene regulation; muscle differentiation; membrane depolarization; acetylcholinesterase
Copyright © 2000 Society for Neuroscience 0270-6474/00/203919-10$05.00/0
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