Electrical Properties of Toad Oocytes During Maturation and Activation

Area of Science:

• Reproductive Biology
• Developmental Biology
• Cellular Physiology

Background:

• Toad oocyte maturation involves complex cellular events, including membrane potential changes and cortical granule breakdown.
• Progesterone triggers meiosis resumption and subsequent developmental milestones in oocytes.

Purpose of the Study:

• To investigate the role of protein synthesis in enabling cortical responses during toad oocyte maturation.
• To determine the timing and dependence of activation potential and cortical granule breakdown on germinal vesicle and protein synthesis.

Main Methods:

• Electrophysiological recordings of membrane potential in Bufo bufo japonicus oocytes.
• Hormone (progesterone) treatment and manipulation of germinal vesicle status.
• Inhibition of protein synthesis using cycloheximide and assessment of cortical responses.

Main Results:

• Oocytes exhibited a significant hyper-polarization after EDTA treatment and depolarization upon progesterone exposure.
• An activation potential was recorded in mature oocytes upon mechanical stimulation or insemination, preceding cortical granule breakdown.
• Inhibition of protein synthesis blocked cortical responses, while germinal vesicle removal did not prevent activation potential generation.

Conclusions:

• Protein synthesis occurring between 9-11 hours post-hormone treatment is essential for enabling cortical responses in toad oocytes.
• These protein syntheses are independent of the germinal vesicle and are critical for events like cortical granule breakdown.