The clock and wavefront model revisited.

Area of Science:

• Developmental Biology
• Systems Biology
• Computational Biology

Background:

• The accepted clock and wavefront model of somitogenesis posits that posterior molecular gradients slow clock oscillations for spatial patterning.
• While molecular clock and wavefront components are identified in the pre-somitic mesoderm (PSM), direct evidence for wavefronts slowing oscillations is lacking.

Purpose of the Study:

• To present an alternative clock and wavefront model for somitogenesis where oscillator coupling is central to slowing oscillations along the anterior-posterior (AP) axis.
• To develop a model with predictive power for gene expression patterns and to test its cross-species applicability.

Main Methods:

• Formulated a new clock and wavefront model based on oscillator coupling.
• Identified three key model parameters measurable from clock period, somite length, and PSM length.
• Simulated experimental perturbations and analyzed gene expression data from zebrafish, chick, mouse, and snake.

Main Results:

• The model predicts a traveling wavefront as an emergent property, slowing oscillations along the AP axis.
• Model predictions for stripe distance and number align with existing zebrafish data.
• A single dimensionless parameter (ratio of coupling strengths) explains variations in patterning profiles across species, with a conserved AP period profile.

Conclusions:

• Oscillator coupling, rather than solely molecular gradients, plays a crucial role in somitogenesis pattern formation.
• The proposed model offers a framework for understanding conserved patterning mechanisms in the PSM across diverse species.
• The model can define a reference frame along the AP axis and predict responses to experimental perturbations.