Abstract
Chemotaxis refers to a process whereby cells move up or down a chemical gradient. Sperm chemotaxis is known to be a strategy exploited by marine invertebrates such as sea urchins to reach eggs efficiently in moving water. Less is understood about how or whether chemotaxis is used by mammalian sperm to reach eggs, where fertilization takes place within the confinement of a reproductive tract. In this report, we quantitatively assessed sea urchin and mouse sperm chemotaxis using a recently developed microfluidic model and high-speed imaging. Results demonstrated that sea urchin Arbacia punctulata sperm were chemotactic toward the peptide resact with high chemotactic sensitivity, with an average velocity Vx up the chemical gradient as high as 20% of its average speed (238 μm/s), while mouse sperm displayed no statistically significant chemotactic behavior in progesterone gradients, which had been proposed to guide mammalian sperm toward eggs. This work demonstrates the validity of a microfluidic model for quantitative sperm chemotaxis studies, and reveals a biological insight that chemotaxis up a progesterone gradient may not be a universal strategy for mammalian sperm to reach eggs.
Highlights
Chemotaxis is a widespread natural phenomenon in which cells or organisms guide their movements according to a chemical gradient in their environment
Our findings revealed that progesterone may not be a universal chemoattractant for mammalian sperm
Extensive efforts were made to test a range of physiological conditions of mouse sperm and a wide range of progesterone concentrations
Summary
Chemotaxis is a widespread natural phenomenon in which cells or organisms guide their movements according to a chemical gradient in their environment. It has been recognized that chemotaxis of sperm toward eggs plays an important role in fertilization in some marine invertebrate species. The marine invertebrates of many species are external fertilizers; that is, they broadcast their sperm and eggs into the surrounding water, which is often moving in nature. Under these conditions, specificity of chemoattractants for conspecific sperm is high in order to avoid interspecies fertilization [7,8] while promoting successful encounters between the sperm and the eggs in moving water. In the sea urchin species Arbacia punctulata, sperm are attracted to resact, a small linear polypeptide that diffuses out from the egg jelly coat [9]. The turn-and-run pattern is regulated by Ca2+ signaling [6]
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