Amphibian Segmentation Clock Models Suggest How Large Genome and Cell Sizes Slow Developmental Rate

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Genomics

Background:

• Evolutionary increases in genome size, cell volume, and nuclear volume are common across life.
• These size increases correlate with a slower developmental tempo, but the underlying mechanisms are unclear.

Purpose of the Study:

• To investigate the molecular mechanisms linking increased genome and nuclear size to slowed developmental tempo.
• To model the impact of genome size on intra-cellular gene expression kinetics during development.

Main Methods:

• Utilized a mathematical model of the somitogenesis clock.
• Adapted the model for two amphibian species with a 10-fold difference in genome size (Xenopus laevis and Ambystoma mexicanum).
• Performed simulations and analytical derivations to identify key parameter changes.

Main Results:

• Identified parameter changes due to increased genome and nuclear size that slow gene expression kinetics.
• Simulations recapitulated slowed gene expression in the larger-genome species (Ambystoma mexicanum) compared to the smaller-genome species (Xenopus laevis).
• Explored the necessity of altered gene product stability and chromatin packing.

Conclusions:

• Slowed degradation rates, increased nuclear volume, and intron length are significant drivers of slowed developmental tempo.
• These factors, linked to genome size, provide a mechanistic explanation for the observed correlation between size and developmental speed.
• Highlights under-explored aspects of nuclear volume and intron length in developmental timing.