Local cell interactions and self-amplifying individual cell ingression drive amniote gastrulation

Area of Science:

• Developmental Biology
• Cell Biology
• Embryogenesis

Background:

• Gastrulation establishes three germ layers (ectoderm, mesoderm, endoderm) through extensive cell movements.
• In amniotes, mesoderm and endoderm formation involves epithelial-to-mesenchymal transition (EMT) at the primitive streak (PS).
• Mechanisms controlling PS formation and maintenance remain poorly understood.

Purpose of the Study:

• To investigate the early events and regulatory mechanisms driving primitive streak formation.
• To elucidate how epithelial-to-mesenchymal transition (EMT) is initiated, amplified, and organized during gastrulation.
• To determine the sufficiency of local cell interactions in explaining primitive streak morphogenesis.

Main Methods:

• Observation of early cellular events in chick embryos.
• Analysis of Nodal signaling pathway involvement.
• Computational modeling and simulations of cell behaviors.

Main Results:

• Epithelial-to-mesenchymal transition (EMT) and cell ingression initiate prior to overt gastrulation.
• A Nodal-dependent 'community effect' concentrates and amplifies EMT, establishing the primitive streak.
• Computer simulations confirm that local cell interactions (EMT, intercalation) suffice for PS formation and cell movements.

Conclusions:

• Primitive streak formation is driven by a positive feedback loop amplifying early EMT events.
• Local cell interactions, rather than long-range signaling, are sufficient to pattern the primitive streak.
• This study provides a mechanistic framework for understanding early amniote gastrulation.