Overdue Calcium Oscillation Causes Polyspermy but Possibly Permits Normal Development in Mouse Eggs

Area of Science:

• Reproductive Biology
• Developmental Biology
• Cellular Physiology

Background:

• Polyspermy in non-mammalian eggs leads to calcium ion (Ca2+) surges and selective sperm nucleus entry for normal embryogenesis.
• The consequences of polyspermy in human in vitro fertilization remain unclear.
• The relationship between polyspermy and calcium ion (Ca2+) oscillations in mammalian eggs is largely unknown.

Purpose of the Study:

• To investigate the impact of impaired calcium ion (Ca2+) oscillation induction on polyspermy in mouse eggs.
• To determine if mouse eggs can undergo normal embryogenesis under conditions of polyspermy caused by defective Ca2+ oscillations.

Main Methods:

• Utilized mouse sperm lacking extramitochondrial citrate synthase (eCS), a Ca2+ oscillation inducer, creating eCS-knockout (eCS-KO) sperm.
• Examined polyspermy rates in both zona pellucida (ZP)-free and ZP-intact mouse eggs.
• Assessed the developmental capacity of eggs resulting from fertilization with eCS-KO sperm.

Main Results:

• eCS-deficient sperm exhibited retarded Ca2+ oscillation initiation.
• Elevated sperm concentrations were found to normalize Ca2+ oscillation initiation.
• eCS deficiency significantly increased polyspermy in both ZP-intact and ZP-free eggs.
• Fertilization with eCS-KO sperm resulted in the production of viable eCS-KO male offspring.

Conclusions:

• Mouse eggs can potentially develop normally under polyspermy conditions, even when Ca2+ oscillations are compromised.
• This finding suggests a degree of resilience in mammalian egg development to polyspermy, mirroring observations in non-mammalian species.
• The study highlights the complex interplay between sperm factors, Ca2+ signaling, and egg activation in mammalian reproduction.