Non-directional radial intercalation dominates deep cell behavior during zebrafish epiboly

Area of Science:

• Developmental biology
• Cell biology
• Vertebrate embryogenesis

Background:

• Epiboly is the initial coordinated cell movement in vertebrate gastrulation.
• Zebrafish epiboly involves enveloping layer (EVL) and deep cell spreading over the yolk.
• A prevailing model posits radial intercalations drive deep cell epiboly.

Purpose of the Study:

• To test the model that radial intercalations drive zebrafish epiboly.
• To analyze 3D cell trajectories and intercalation dynamics during epiboly.
• To investigate epiboly defects in MZspg mutant embryos.

Main Methods:

• Global 3D cell trajectory recording of zebrafish blastomeres.
• Image analysis framework using Voronoi diagrams for intercalation analysis.
• Spatio-temporal modeling and anatomical coordinate system fitting.

Main Results:

• Deep cell intercalations show no directional bias towards or away from the EVL.
• Intercalation direction is independent of previous cell intercalation history.
• Epiboly defects in MZspg mutants are not explained by altered intercalation behavior.

Conclusions:

• Radial intercalations do not appear to be directed towards the EVL in zebrafish epiboly.
• A dynamic model where deep cells migrate into available space is supported.
• Genetic programs controlling cell motility likely regulate deep cell behavior and epiboly progression.