Sperm maturation in vitro: co-culture of spermatozoa and epididymal epithelium.

Sperm maturation involves an intimate interaction between spermatozoa and the epididymal epithelium. Aspects of this relationship can be examined by co-incubating epididymal spermatozoa with epididymal epithelium in vitro. Plaques of epididymal epithelium from a variety of species (for example rodents, dogs, humans) can be maintained in culture medium supplemented with growth factors and androgens. When co-incubated with these epithelial cultures, immature epididymal spermatozoa undergo maturation changes that lead to the acquisition of progressive motility, zona binding and, in some instances, fertilizing capacity in vitro. The use of such co-culture techniques for the understanding of sperm maturation in vitro and in vivo is reviewed with reference to recent experiments.