Wave of free calcium at fertilization in the sea urchin egg visualized with fura-2

Area of Science:

• Cell Biology
• Developmental Biology
• Biophysics

Background:

• Fertilization triggers a calcium (Ca2+) wave in eggs of many species.
• The precise visualization and characteristics of this wave in sea urchins were previously limited.

Purpose of the Study:

• To demonstrate and visualize the calcium wave front during fertilization in the sea urchin Lytechinus pictus.
• To analyze the spatial and temporal dynamics of the Ca2+ wave with high resolution.

Main Methods:

• Utilized the fluorescent calcium chelator fura-2.
• Employed low-light-level TV microscopy and digital image processing.
• Excited fura-2 at 340 nm (increased fluorescence) and 380 nm (reduced fluorescence) to visualize Ca2+ dynamics.

Main Results:

• Successfully visualized a wave front of increased free calcium traversing the Lytechinus pictus egg upon fertilization.
• Observed a band-like Ca2+ wave, consistent with findings in other species' eggs.
• In dispermic eggs, two distinct Ca2+ waves were identified originating from separate sperm entry points.

Conclusions:

• The study confirms and visualizes the calcium wave phenomenon in sea urchin fertilization.
• The high-resolution imaging technique provides detailed insights into Ca2+ dynamics during egg activation.
• Findings contribute to understanding the role of calcium signaling in early embryonic development.