Abstract
Although intact spermatozoon is successfully collected from infertile patients, repeated implantation failure or pregnancy loss are often experienced. Sperm nuclear defects have been thought to be one of the most important reasons for repeated assisted reproductive technology failure. In comparison with other mammalians, characteristic heterogeneity has been found in each mature human sperm nuclei, therefore it is necessary to investigate the significance between fertilization failure, developmental disability and structural abnormality of human sperm nuclei. Furthermore, if close relationships between the heterogeneity of human ejaculated sperm nuclei and DNA fragmentation are defined by analyzing sperm nucleoproteins, it would be clearly shown that impaired sperm chromatin leads to failure of embryo development in vitro or in vivo, so called late paternal effect on embryo development. It will be necessary in the near future to study the strategy for more novel methodology than those previously reported in terms of sperm selection. The present report reviews the roles of mammalian sperm nuclear structure, especially in humans, in fertilization and embryo development after the insemination procedure. (Reprod Med Biol 2006; 5: 161-168).