Alternative strategies for the long-term preservation of spermatozoa.

A number of perceived future requirements for stored germplasm in agriculture, aquaculture, biotechnology and conservation are discussed in the present review. In the light of these broad demands, it is apparent that current approaches to gamete and embryo storage need considerable improvement, and that novel approaches to the technologies of germplasm preservation should be pursued if possible. The present article is presented in response to a request for novel future research ideas in this area. Early literature on desiccation, and later research into natural mechanisms of survival during desiccation, is considered in relation to the development of freeze-drying and vitrification methods. Developments in reproductive technologies themselves may mean that freeze-dried spermatozoa could realistically be used for direct intracytoplasmic microinjection of oocytes. Other radical methods that may achieve germplasm preservation are harvesting testicular cells in culture, cryopreserving immature or seasonally regressed testicular material, or a combination of both. Evidence from non-mammalian testicular culture systems, and recent success with the transmeiotic development of mouse spermatids in vitro, suggest that these approaches may eventually become feasible.