Reproduction Abstracts

The origin of a new organism requires the fusion of the female’s oocyte with the male’s sperm. The oocyte increases the chance for an encounter with a sperm by the release of chemoattractants, which provide chemical cues for the sperm to spot the egg. This mechanism termed ‘sperm chemotaxis’ is important for fertilization in many species. Sea urchins have served as a model organism for fertilization, in particular for sperm chemotaxis, since the early 20th century. Sea urchin sperm provide a powerful model to unveil both the cellular principles underlying chemosensation at the physical sensitivity limit and the computational operations performed by sperm during chemotactic steering. Whereas sea urchin sperm rely on chemotaxis, mammalian sperm seem to navigate along both chemical and physical cues within the female genital tract; chemo-, thermo-, rheotaxis, and combinations thereof have been proposed. Some signalling components are conserved between sea urchin and mammalian sperm, but the sensing mechanisms are distinctively different. In fact, in mammalian sperm, the navigation mechanism(s) and underlying signaling pathways are rather ill-defined, due to the demanding challenge to experimentally emulate the complex chemical, hydrodynamic, and topographical landscape of the female genital tract.