Morphogenetic pattern formation during ascidian notochord formation is regulative and highly robust

Area of Science:

• Developmental Biology
• Chordate Embryogenesis
• Morphogenesis

Background:

• The ascidian notochord, a precursor to the vertebrate spine, forms via simultaneous invagination and convergent extension.
• Understanding the interplay between intrinsic cellular behaviors and extrinsic tissue interactions is crucial for deciphering notochord development.

Purpose of the Study:

• To investigate how notochord-intrinsic morphogenetic behaviors and interactions with surrounding tissues dictate notochord formation patterns.
• To elucidate the regulative capacity of ascidian notochord development.

Main Methods:

• Micromanipulation of isolated notochord rudiments.
• Time-lapse and confocal microscopy to observe cell and tissue dynamics.
• Analysis of notochord formation in embryos with specific tissue ablations or alterations.

Main Results:

• Isolated notochord rudiments initiate cell division and motility but fail to invaginate or extend without external tissue contact.
• Notchords can form and extend a rod when in basal contact with various tissues (neural plate, endoderm, mesenchyme, or mesoderm).
• The axis of convergent extension and associated cell behaviors are influenced by the specific contacting tissues, indicating a regulative developmental process.

Conclusions:

• Ascidian notochord formation is a highly regulative process, dependent on both intrinsic cellular properties and instructive/permissive interactions with neighboring tissues.
• The specific tissue environment significantly influences the trajectory and patterns of notochord morphogenesis.
• These findings offer insights into the evolution of notochord development within the chordate phylum.