Application of caged compounds and high speed fluorescence imaging to the study of sperm motility regulation

Abstract

Sperm are highly differentiated cells adapted to perform one specific role: to fertilize the egg. Despite their small size, sperm have the ability to precisely recognize physicochemical signals from the environment and the female reproductive organs and respond in a specific and regulated manner. Therefore, sperm are often considered to be comparable to the sensory neurons. Motility is one of the most important sperm functions and its defect directly leads to infertility. To study sperm motility regulation in detail, we developed a high-speed fluorescence imaging system based around stroboscopic illumination with a light-emitting diode (LED). We also developed several caged compounds (ligands and second messengers) to rapidly stimulate sperm without causing any turbulence in the surrounding medium, a major limitation of classical bath application protocols. Using these techniques, we induced a chemotaxis-like motility response in sea urchin sperm and confirmed that sperm flagella become more asymmetric when the flagellar intracellular Ca²⁺ concentration increases. The advantages of our imaging system and the insights it has revealed regarding sperm motility regulation will be summarized. [J Physiol Sci. 2008;58 Suppl:S61]