In vivo versus in vitro fertilization

The complex sequence of biological steps involved in reproduction in vivo is only partially reproduced in current IVF procedures. In fact, events playing a key role in vivo such as male gamete selection can only be partially mimicked in vitro. To understand the role played by the mammalian oviduct in sperm storage and selection several in vitro sperm-oviductal cell co-culture systems have been developed. Particular sperm subpopulations have been reported to be selected by in vitro cultured oviductal cells through cell-cell adhesion, in different species. In the bovine, in vitro selected sperm have been demonstrated to be endowed with a superior zona pellucida binding and fertilization competence. In conclusion, research on in vitro sperm oviduct interaction may provide new basic information about early reproductive events allowing the development of alternative methods for a more physiological sperm selection in assisted reproductive biotechnologies. (C) 2004 Elsevier Ireland Ltd. All rights reserved.