A mechanical model of early somite segmentation

Area of Science:

• Developmental biology
• Cellular mechanics
• Embryogenesis

Background:

• The clock-and-wavefront (CW) model describes somitogenesis but doesn't explain cellular rearrangement.
• Molecular signaling's role in organizing pre-somitic mesoderm (PSM) into somites remains unclear.

Purpose of the Study:

• To elucidate the cellular and mechanical mechanisms underlying somite formation in chicken embryos.
• To propose and validate a novel model for PSM segmentation.

Main Methods:

• Scanning electron microscopy (SEM) of chicken embryos.
• Analysis of epithelialization and cell behavior in the dorsal PSM.
• Development of a mechanical instability model for segmentation.

Main Results:

• Identified a caudally-progressing epithelialization front in the dorsal PSM preceding somite formation.
• Observed apical constriction and segmentation signs 3-4 somite lengths caudal to the last somite.
• Proposed a model where increasing apical contractility leads to periodic adhesion failures, defining inter-somite boundaries.

Conclusions:

• The mechanical instability model explains somite segmentation through periodic adhesion failures driven by contractility.
• Segment size and regularity are determined by the ratio of contractility buildup rate (Λ) to contraction front speed (F).
• This mechanism offers a physical explanation for the spatial periodicity and size regulation during somitogenesis.