Dry Preservation of Spermatozoa: Considerations for Different Species

Abstract

The current gold standard for sperm preservation is storage at cryogenic temperatures. Dry preservation is an attractive alternative, eliminating the need for ultralow temperatures, reducing storage maintenance costs, and providing logistical flexibility for shipping. Many seeds and anhydrobiotic organisms are able to survive extended periods in a dry state through the accumulation of intracellular sugars and other osmolytes and are capable of returning to normal physiology postrehydration. Using techniques inspired by nature's adaptations, attempts have been made to dehydrate and dry preserve spermatozoa from a variety of species. Most of the anhydrous preservation research performed to date has focused on mouse spermatozoa, with only a small number of studies in nonrodent mammalian species. There is a significant difference between sperm function in rodent and nonrodent mammalian species with respect to centrosomal inheritance. Studies focused on reproductive technologies have demonstrated that in nonrodent species, the centrosome must be preserved to maintain sperm function as the spermatozoon centrosome contributes the dominant nucleating seed, consisting of the proximal centriole surrounded by pericentriolar components, onto which the oocyte's centrosomal material is assembled. Preservation techniques used for mouse sperm may therefore not necessarily be applicable to nonrodent spermatozoa. The range of technologies used to dehydrate sperm and the effect of processing and storage conditions on fertilization and embryogenesis using dried sperm are reviewed in the context of reproductive physiology and cellular morphology in different species.

Keywords: ambient preservation; biobanking; biostabilization; dehydration; spermatozoa.

FIG. 1.

Illustration of DNA supercompaction and centrosomal reduction during spermatogenesis. Supercompaction of the nuclear DNA is achieved through the replacement of lysine-rich histones with smaller more basic arginine and cysteine-rich protamines. Protamines further compact the DNA through the formation of disulfide bonds during maturation through the epididymis. In nonrodent mammalian species, there is partial reduction of the male centrosome. The distal centriole is reduced during spermatogenesis, resulting in the presence of only the proximal centriole in the mature spermatozoon.