Effects of freezing and activation on membrane quality and DNA damage in Xenopus tropicalis and Xenopus laevis spermatozoa

There is growing concern over the impact of sperm cryopreservation on DNA integrity, and the subsequent development of offspring generated from this cryopreserved material. In this study, membrane integrity and DNA stability of Xenopus laevis and Xenopus tropicalis spermatozoa were evaluated in response to cryopreservation with or without activation, a process that happens upon exposure to water to spermatozoa of some aquatic species. A dye exclusion assay revealed that sperm plasma membrane integrity in both species decreased after freezing, more so in X. laevis spermatozoa than X. tropicalis. The sperm chromatin dispersion (SCD) test showed that for both X. tropicalis and X. laevis activated, frozen spermatozoa produced the highest levels of DNA fragmentation compared to all fresh samples and frozen, non-activated samples (P < 0.05). Understanding the nature of DNA and membrane damage that occurs in cryopreserved spermatozoa from Xenopus species represents the first step in exploiting these powerful model organisms to understand the developmental consequences of fertilizing with cryopreservation-damaged spermatozoa.