Cortical activity in vertebrate eggs. I: The activation waves

Area of Science:

• Developmental Biology
• Biophysics
• Cellular Mechanics

Background:

• Vertebrate eggs exhibit complex surface wave phenomena, including calcium waves and mechanical deformations.
• Previous research suggested calcium-stimulated calcium-release as the driver for Medaka egg calcium waves.
• Actomyosin gel dynamics were implicated in the mechanical wave pair observed on Xenopus egg surfaces.

Purpose of the Study:

• To present a physical model for the propagation of chemical and mechanical waves on vertebrate egg surfaces.
• To mathematically formulate the calcium-stimulated calcium-release hypothesis for Medaka eggs.
• To propose and simulate a mechanism for the mechanical wave pair in Xenopus eggs based on actomyosin gel physical chemistry.

Main Methods:

• Mathematical formulation of the calcium-stimulated calcium-release hypothesis.
• Analysis of wavefront data to map cortical reactivity.
• Computer simulation of gel expansion and contraction based on physical chemistry equations.

Main Results:

• A map of cortical reactivity for Medaka eggs was generated, showing a gradient from animal to vegetal hemispheres.
• The model explains the lag between swelling and contraction in Xenopus eggs due to differing kinetics.
• Computer simulations successfully mimicked chemical and mechanical wave propagation.

Conclusions:

• The physical model provides a framework for understanding wave propagation on vertebrate egg surfaces.
• Cortical reactivity exhibits a hemispheric gradient in Medaka eggs.
• The model offers a method for diagnosing egg cortex mechanochemical properties using observed waves.