[The dorsoventral inversion: An attempt of synthesis]

Area of Science:

• Evolutionary developmental biology
• Comparative embryology
• Developmental biology

Background:

• The evolutionary origin of body plans in invertebrates and vertebrates has been debated, with early hypotheses of body plan inversion facing significant opposition.
• Understanding the differences between hyponeurian (invertebrates) and epineurian (echinoderms, chordates, vertebrates) body plans is crucial for evolutionary studies.

Observation:

• Comparative analysis of gastrulation in arthropods, amphibians, echinoderms, and mammals reveals both differences and commonalities.
• The dorsoventral gradient, regulated by specific gene pathways, appears inverted in epineurians compared to arthropods.
• Blastopore invagination and BMP signaling pathways show distinct patterns between protostomes and deuterostomes, suggesting evolutionary divergence.

Findings:

• The study supports Etienne Geoffroy Saint Hilaire's hypothesis of a body plan inversion between protostomes and deuterostomes.
• Gastrulation processes and the orientation of key developmental events like blastopore invagination differ significantly between these groups.
• The oral cavity in deuterostomes may represent a novel structure linked to the branchial system, evolving from developmental differences.

Implications:

• This research provides a framework for understanding the evolutionary chronology of body plan modifications.
• It highlights the importance of comparative embryology and developmental biology in resolving long-standing evolutionary questions.
• The findings contribute to a deeper understanding of the fundamental differences in embryonic development across major animal lineages.