Actin-mediated surface motility during sea urchin fertilization

Area of Science:

• Cell Biology
• Developmental Biology
• Biochemistry

Background:

• Sea urchin eggs serve as a model for actin-mediated surface activity.
• Unfertilized eggs possess numerous short microvilli supported by actin oligomers.

Purpose of the Study:

• To investigate actin-mediated surface activity during sea urchin egg fertilization.
• To understand the role of actin assembly in sperm incorporation and early cell division.

Main Methods:

• Electron microscopy to visualize microvilli.
• Rhodamine-labeled phalloidin staining to detect actin polymerization.
• Treatment with cytochalasin to inhibit actin assembly.
• Quantitative fluorescence microscopy to analyze microfilament changes.

Main Results:

• Actin assembly is essential for fertilization cone formation and sperm incorporation.
• Cytochalasin treatment prevents sperm incorporation but not egg activation.
• Post-fertilization, massive actin polymerization causes microvillar elongation.
• Cytokinesis involves microfilament reorganization, not necessarily increased actin.

Conclusions:

• Actin-membrane interactions are critical throughout sea urchin fertilization and early development.
• Localized and global actin assembly orchestrates key events like sperm entry and cell division.
• Sea urchin eggs provide a valuable system for studying fundamental actin dynamics.