Collective Cell Sorting Requires Contractile Cortical Waves in Germline Cells.

Area of Science:

• Developmental Biology
• Cell Biology
• Reproductive Biology

Background:

• Primordial follicles (mammals) and egg chambers (Drosophila) are basic units of female reproduction, formed by germline cells encapsulated by somatic cells.
• The coordination mechanisms between germline and somatic tissues during morphogenesis of these units are not well understood.

Purpose of the Study:

• To investigate the cellular mechanisms underlying the coordinated morphogenesis of germline and somatic tissues during egg chamber formation in Drosophila.
• To elucidate the role of germline cell cortical activities and cell-cell adhesion in the encapsulation process.

Main Methods:

• Utilized advanced live imaging techniques in Drosophila ovaries.
• Performed genetic perturbations to analyze the function of cortical contractility, bleb protrusion, and cadherin-based adhesion.
• Assessed the impact of these perturbations on germline cyst sorting and encapsulation.

Main Results:

• Discovered periodic actomyosin waves and pressure-release blebs at the germ cell cortex, crucial for sorting germline cysts.
• Demonstrated that germline cortical activities and adhesion are essential for proper encapsulation, preventing defects like under- or over-encapsulation and cyst splitting.
• Showed that reduced germline contractility or adhesion leads to decreased cyst stiffness, improper anchoring, and passive deformation by somatic cells.
• Identified active forward migration of germline cysts under conditions of increased germline activity or blocked somatic cell constriction.

Conclusions:

• Germline cells actively participate in physical coupling with somatic cells during female gamete formation.
• Cortical contractility and adhesion in germ cells are critical for their collective sorting and proper encapsulation into functional reproductive units.
• The findings reveal a novel mechanism where germ cells play an active role in their own morphogenesis within the ovarian context.