Free calcium wave upon activation in Xenopus eggs

Area of Science:

• Developmental Biology
• Cell Biology
• Biophysics

Background:

• The activation of Xenopus laevis eggs involves complex cellular events.
• Understanding the spatiotemporal dynamics of calcium release is crucial for deciphering egg activation.

Purpose of the Study:

• To map the spatial and temporal patterns of free calcium release in Xenopus laevis egg cortex upon artificial activation.
• To correlate the calcium wave with the previously described egg activation wave.

Main Methods:

• Xenopus laevis eggs were microinjected with the calcium-sensitive photoprotein aequorin.
• A photonic microscope system coupled with a 2D photon-counting system and image processor was used to detect aequorin luminescence.
• Simultaneous imaging of aequorin luminescence and egg surface changes under incident light was performed.

Main Results:

• Artificial activation initiated a free calcium increase at the point of activation.
• This calcium increase propagated as a wave through the cortical cytoplasm at approximately 8 microns/sec.
• The spatial pattern of the calcium wave closely resembled the egg's activation wave, with the calcium increase zone corresponding to the relaxation zone where exocytosis occurred.

Conclusions:

• Free calcium release in Xenopus laevis eggs occurs as a propagating wave.
• The calcium wave is temporally and spatially correlated with the egg activation wave.
• Calcium influx is a key event driving cortical granule exocytosis and microvilli elongation during egg activation.