Interface extension is a continuum property suggesting a linkage between AP contractile and DV lengthening processes

Area of Science:

• Developmental biology
• Cell biology
• Biophysics

Background:

• Axis elongation in early Drosophila embryos relies on cell intercalation.
• This process involves anterior-posterior (AP) interface contraction and dorsal-ventral (DV) interface extension.
• Mechanisms of DV interface elongation are less understood than AP interface contraction.

Purpose of the Study:

• To investigate the mechanisms of new dorsal-ventral (DV) interface elongation during Drosophila germband development.
• To determine if DV interface elongation is a distinct process from AP interface contraction.

Main Methods:

• Live imaging of Drosophila embryos.
• Analysis of cell behaviors, including interface dynamics and vertex formation.
• Investigating the role of cortical F-actin and medial myosin in interface elongation.

Main Results:

• DV interface elongation initiates concurrently with AP interface contraction.
• Newly formed DV interfaces elongate through ratchet-like sliding, similar to AP interfaces.
• Cortical F-actin networks are crucial for the oscillations driving this sliding.
• Medial myosin generates oscillating radial forces, creating asymmetries at tricellular vertices.

Conclusions:

• DV interface elongation is not a separate process but shares mechanisms with AP interface contraction.
• Directional ratcheted sliding, driven by cell forces and planar polarized stabilization, generates both AP contraction and DV elongation.
• This unified mechanism challenges canonical models of axis elongation.