Fertilization without spermatozoa

Mammalian spermatozoa first acquire the ability to fertilize oocytes as the y pass through the epididymis to mature. Due to recent advances in microins emination techniques, not only mature spermatozoa, but also immature sperm cells at certain stages in the testis, have been used to construct diploid zygotes, some of which subsequently develop to normal offspring. Using roun d spermatids, the most youngest haploid male germ cells, normal births have been reported in the mouse, rabbit, and human. Furthermore, in the mouse, secondary and primary spermatocytes also support full term development afte r incorporation into immature or mature homologous oocytes. Spermatogenic c ells of several species can be cryopreserved easily in simple cryoprotectan t solutions. Thus, the microinsemination techniques using spermatogenic cel ls give us a way to treat infertility, and provide valuable information on gametogenesis, including spermatogenesis, meiosis, and genomic imprinting.