Origin and evolution of endoderm and mesoderm.

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Genetics

Background:

• Germ layers (endoderm, mesoderm) form during early animal development (gastrulation) and give rise to all adult tissues and organs.
• The evolutionary origin and relationship of the inner germ layers, endoderm and mesoderm, remain a subject of long-standing debate.

Purpose of the Study:

• To review major modes of endoderm and mesoderm formation across Metazoa and propose evolutionary scenarios for the ancestral state.
• To investigate the homology of endoderm and mesoderm among Bilateria by analyzing key transcription factors.

Main Methods:

• Comparative analysis of crucial transcription factors (GATA 4-6, twist, snail, brachyury) involved in early germ layer specification and differentiation.
• Summarizing the roles of these genes in mesendoderm formation across different taxa.

Main Results:

• Identification of major modes of endoderm and mesoderm formation in Metazoa.
• Analysis suggests that homologous gene regulatory networks, involving conserved transcription factors, likely underlie mesendoderm development in Bilateria.
• The functions of key genes in germ layer formation appear to have evolved from the regulation of fundamental cellular processes.

Conclusions:

• Comparative analysis of transcription factors provides insights into the homology of endoderm and mesoderm in Bilateria.
• The evolution of endoderm and mesoderm formation is linked to the regulation of basic cellular properties like adhesion, motility, cytoskeleton, and cell cycle.