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Effects of cooling, cryopreservation and heating on sperm proteins, nuclear DNA, and fertilization capability in mouse

In the present study, we used confocal microscopy and electrophoresis to study the effects of heating to 5 or 100°C or cooling to 4°C or − 196°C on the stability of sperm proteins and DNA. We used intracytoplasmic sperm injection (ICSI) to determine the fertilizing capability of treated spermatoza. It was shown that sperm cryopreservation at − 196°C or cooling at 4°C altered neither protein and DNA profiles nor the sperm fertilization capability, while the protein and DNA profiles of sperm heated at 100°C were irreversibly degraded and inactivated. The proteins of sperm were severely damaged while the nuclear DNA still maintained its integrity when heated to 58°C. Observation by laser confocal microscopy showed that after being heated to 58°C and 100°C, the nuclear of mouse sperm lost their ability to activate oocytes and they could not transform to male pronuclei though the membrane of some sperm could degrade and induce the formation of sperm asters in ICSI oocytes. The results indicate that the use of 58°C heating only causes the degradation of sperm proteins, while the 100°C heating elicits the irreversible degradation of both sperm proteins and nuclear DNA, and the damage of sperm proteins is primarily responsible for the observed decrease in sperm fertilizing capability. Mol. Reprod. Dev. © 2005 Wiley‐Liss, Inc.