Dynamic myosin phosphorylation regulates contractile pulses and tissue integrity during epithelial morphogenesis

Area of Science:

• Cell Biology
• Developmental Biology
• Biophysics

Background:

• Apical constriction is a fundamental cell shape change driving epithelial tube formation.
• Nonmuscle myosin II (Myo-II) activation by kinases like Rho-associated kinase (Rok) generates contractile forces for apical constriction.
• Myosin II (Myo-II) assembly and disassembly cycles (pulses) occur during epithelial morphogenesis, but their regulatory mechanisms and functional importance remain unclear.

Purpose of the Study:

• To investigate the role of Myosin II (Myo-II) phosphoregulation in organizing contractile pulses during epithelial morphogenesis.
• To determine if Myo-II pulses are functionally required for tissue integrity and development.

Main Methods:

• Utilized Drosophila melanogaster gastrulation as a model system.
• Generated mutants mimicking constitutive Myo-II light chain phosphorylation.
• Depleted myosin phosphatase to assess its role in Myo-II pulsing.
• Observed actomyosin dynamics and tissue morphology using live imaging.

Main Results:

• Demonstrated that Myo-II pulses are coupled to apical Rho-associated kinase (Rok) pulses.
• Showed that mimicking Myo-II phosphorylation or inhibiting myosin phosphatase disrupts Myo-II contractile pulses and actomyosin organization.
• Found that constitutive Myo-II phosphorylation leads to continuous, non-incremental apical constriction.
• Observed failure in maintaining intercellular actomyosin network connections in mutants with altered pulsing.

Conclusions:

• Dynamic Myo-II phosphorylation, controlled by upstream signals, is crucial for organizing contractile Myo-II pulses in space and time.
• Myo-II pulses are essential for maintaining tissue integrity during epithelial morphogenesis, likely by regulating actomyosin network dynamics.