Abstract
Actin filament assembly in nonmuscle cells is regulated by the actin polymerization machinery, including the Arp2/3 complex and formins. However, little is known about the regulation of actin assembly in muscle cells, where straight actin filaments are organized into the contractile unit sarcomere. Here, we show that Fhod3, a myocardial formin that localizes to thin actin filaments in a striated pattern, regulates sarcomere organization in cardiomyocytes. RNA interference-mediated depletion of Fhod3 results in a marked reduction in filamentous actin and disruption of the sarcomeric structure. These defects are rescued by expression of wild-type Fhod3 but not by that of mutant proteins carrying amino acid substitution for conserved residues for actin assembly. These findings suggest that actin dynamics regulated by Fhod3 are critical for sarcomere organization in striated muscle cells.
Highlights
In striated muscle, thin actin filaments and thick filaments of myosin are highly organized to form myofibrils [1] (Fig. 1A)
Because an unbranched straight actin filament is the major form in striated muscle cells, it is possible that a formin family protein serves as the key regulator of actin dynamics in myofibrils
As shown in the present study, Fhod3 in cardiomyocytes localizes to thin actin filaments, to areas near the middle of the sarcomere
Summary
Thin actin filaments and thick filaments of myosin are highly organized to form myofibrils [1] (Fig. 1A). Little is known about the regulation of actin assembly in muscle cells, where straight actin filaments are organized into the contractile unit sarcomere. We show that Fhod3, a myocardial formin that localizes to thin actin filaments in a striated pattern, regulates sarcomere organization in cardiomyocytes.
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