Protein phosphatase activity is necessary for myofibrillogenesis.

During myofibrillogenesis, myosin light-chain kinase (MLCK) phosphorylates the regulatory light chain (RLC) of myosin II, enabling patterned assembly of myosin thick filaments. Aprotein phosphatase (PP) has been shown to mediate RLC dephosphorylation in adult smooth and striated muscle. A role for PP activity in regulating myofibrillogenesis during embryonic development, however, has not been investigated.

Calcium transients regulate titin organization during myofibrillogenesis.

Titin has a Ca2+-dependent kinase domain and may act as a molecular template for myofibrillogenesis. Therefore, we examined the relationship between endogenous Ca2+ transients and titin organization in embryonic myocytes. When transients were blocked during sarcomere assembly, titin organization was disrupted.

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.

Skeletal muscle myosin cross-bridge cycling is necessary for myofibrillogenesis.

A major stimulus affecting myofibrillogenesis in both embryonic and mature striated muscle is contractile activity. There are two major signals associated with contractile activity: a physiological signal, the transient increase in intracellular calcium, and a physical signal, the transient increase in tension production. However, dissociating these two signals to examine their relative contributions to myofibrillogenesis has proven difficult.