Freeze-dried sperm fertilization leads to full-term development in rabbits

Abstract

To date, the laboratory mouse is the only mammal in which freeze-dried spermatozoa have been shown to support full-term development after microinjection into oocytes. Because spermatozoa in mice, unlike in most other mammals, do not contribute centrosomes to zygotes, it is still unknown whether freeze-dried spermatozoa in other mammals are fertile. Rabbit sperm was selected as a model because of its similarity to human sperm (considering the centrosome inheritance pattern). Freezedrying induces rabbit spermatozoa to undergo dramatic changes, such as immobilization, membrane breaking, and tail fragmentation. Even when considered to be "dead" in the conventional sense, rabbit spermatozoa freeze-dried and stored at ambient temperature for more than 2 yr still have capability comparable to that of fresh spermatozoa to support preimplantation development after injection into oocytes followed by activation. A rabbit kit derived from a freeze-dried spermatozoon was born after transferring 230 sperm-injected oocytes into eight recipients. The results suggest that freeze-drying could be applied to preserve the spermatozoa from most other species, including human. The present study also raises the question of whether rabbit sperm centrosomes survive freeze-drying or are not essential for embryonic development.