Time-lapse analysis and mathematical characterization elucidate novel mechanisms underlying muscle morphogenesis

Area of Science:

• Developmental Biology
• Cellular Biology
• Biochemistry

Background:

• Skeletal muscle development involves transforming precursor cells into multinucleate myotubes.
• While muscle specification is understood, the mechanisms of muscle fiber elongation and factors limiting it remain unclear.

Purpose of the Study:

• To define the cellular and molecular mechanisms underlying skeletal muscle fiber morphogenesis in zebrafish.
• To identify molecular factors that regulate muscle fiber elongation and orientation.

Main Methods:

• Observation of zebrafish fast muscle fiber development.
• Genetic analysis using laminin mutant embryos.
• Genetic mosaic analysis to assess cell-autonomy.

Main Results:

• Muscle fiber morphogenesis occurs in three phases: precursor cell stage, intercalation/elongation, and boundary capture/myotube formation.
• Elongation involves repetitive protrusion extension and filling until myotendinous junction attachment.
• Laminin is essential for efficient elongation, fiber orientation, and boundary capture, with different laminin chains having distinct roles.

Conclusions:

• Muscle fiber elongation is a phased process driven by protrusion extension and filling.
• Laminin is a key regulator of muscle fiber orientation and length.
• Boundary capture is a cell-autonomous process.