Modularity and dissociation in the evolution of gene expression territories in development

Area of Science:

• Developmental biology
• Evolutionary developmental biology
• Marine biology

Background:

• Modularity is a key feature of embryonic development and evolution.
• Gene expression territories partition cells into functional units during development.
• Sea urchin embryos provide a model for studying developmental modularity.

Purpose of the Study:

• To investigate gene expression territories in the direct-developing sea urchin Heliocidaris erythrogramma.
• To compare these territories with those of the indirect-developing pluteus larva.
• To understand the evolutionary mechanisms of developmental modules.

Main Methods:

• Analysis of cell lineage data in H. erythrogramma.
• Examination of gene expression patterns in H. erythrogramma.
• Hybridization experiments using H. erythrogramma and Heliocidaris tuberculata.

Main Results:

• Skeletogenic cell, coelomic, and vegetal plate gene expression territories are conserved in H. erythrogramma.
• These territories originate from different cell lineages compared to the pluteus.
• The oral ectodermal territory, present in pluteus larvae, is absent in H. erythrogramma but restored in hybrids.

Conclusions:

• Embryonic modules evolve via changes in dominant regulatory gene expression within territories.
• Entire developmental modules can be lost during the evolution of embryos.
• Developmental modularity provides insights into evolutionary pathways.