Calcium transients regulate patterned actin assembly during myofibrillogenesis.
The highly ordered arrangement of sarcomeric myosin during striated muscle development requires spontaneous calcium (Ca(2+)) transients. Here, we show that blocking transients also compromises patterned assembly of actin thin filaments, titin, and capZ. Because a conserved temporal assembly pattern has been described for these proteins, selective inhibitors of either thick or thin filament formation were used to determine their relative temporal interdependencies. For example, inhibition of myosin light chain kinase (MLCK) by application of a specific inhibitory peptide or phorbol myistate acetate (PMA) disrupts myosin assembly without significantly affecting formation of actin bands. The MLCK inhibitor ML-7, however, disrupted actin as well as myosin. Surprisingly, agents that interfere with actin dynamics, such as cytochalasin D, produced only minor organizational disruptions in actin, capZ, and titin staining. However, cytochalasin D and other actin disrupting compounds significantly perturbed myosin organization. The results indicate that (1) Ca(2+) transients regulate one or more of the earliest steps in sarcomere formation, (2) mature actin filaments can assemble independently of myosin band formation, and (3) myosin thick filament assembly is extremely sensitive to disruption of either the actin or titin filament systems.
Li
Hongyan
H
Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, USA.
Cook
John D
JD
Terry
Monica
M
Spitzer
Nicholas C
NC
Ferrari
Michael B
MB
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D000199:Actins / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D051347:CapZ Actin Capping Protein; D064211:Connectin; D015638:Cytochalasin D / Q000494:pharmacology; D047630:Depsipeptides; D008840:Microfilament Proteins / Q000378:metabolism; D024510:Muscle Development / Q000187:drug effects / Q000502:physiology*; D009124:Muscle Proteins / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D014981:Xenopus / Q000196:embryology / Q000378:metabolism*
D000199:Actins; D001381:Azepines; D019086:Bridged Bicyclo Compounds, Heterocyclic; D051347:CapZ Actin Capping Protein; D064211:Connectin; D047630:Depsipeptides; D008840:Microfilament Proteins; D009124:Muscle Proteins; D009281:Naphthalenes; D010456:Peptides, Cyclic; D013844:Thiazoles; D053778:Thiazolidines; C057531:jasplakinolide; C070571:ML 7; D015638:Cytochalasin D; D011494:Protein Kinases; D009219:Myosin-Light-Chain Kinase; D009218:Myosins; D013755:Tetradecanoylphorbol Acetate; C037067:latrunculin A