Clearing the way to implantation.

The endocrine symphony known as the reproductive life cycle consists of a complex series of hormonally driven “movements.” The sole rationale for the reproductive cycle is the generation of a fertilizable ovum and, contingent upon fertilization, the establishment of implantation and of an ongoing gestation. Although fecundity rates vary among species, there can be little question as to the ongoing success of sexual reproduction. As might be expected given their complexity, the reproductive cycle and the attendant sexual reproductive process are vulnerable to breaking down at key points. For this reason, genetic analysis of organisms with attenuated or enhanced reproductive patterns has shed considerable light on the wild-type state. Increasingly over the last two decades, the complementary strategy of reverse genetics — generally by targeted gene deletion in the mouse — has allowed researchers to examine the physiological roles of molecules presumed to act in the reproductive cycle.