Fertilization of sea urchin eggs and sperm motility are negatively impacted under low hypergravitational forces significant to space flight

Sperm and other flagellates swim faster in microgravity (muG) than in 1 G, raising the question of whether fertilization is altered under conditions o f space travel. Such alterations ave implications for reproduction of plant and animal food and for long-term space habitation by man. We previously d emonstrated that muG accelerates protein phosphorylation during initiation of sperm motility but delays the sperm response to the egg chemotactic fact or, speract. Thus sperm are sensitive to changes in gravitational force. Ne w experiments using the NiZeMi centrifugal microscope examined whether low hypergravity (hyperG) causes effects opposite to muG on sperm motility, sig nal transduction, and fertilization. Sperm % motility and straight-line vel ocity were significantly inhibited by as little as 1.3 G. The phosphorylati on states of FP130, an axonemal phosphoprotein, and FP160, a cAMP-dependent salt-extractable flagellar protein, both coupled to motility activation, s howed a more rapid decline in hyperG. Most critically, hyperG caused a simi lar to 50% reduction in both the rate of sperm-egg binding and fertilizatio n. The similar extent of inhibition of both fertilization parameters in hyp erG suggests that the primary effect is on sperm rather than eggs. These re sults not only support our earlier muG data demonstrating that sperm are se nsitive to small changes in gravitational forces but more importantly now s how that this sensitivity affects the ability of sperm to fertilize eggs. T hus, more detailed studies on the impact of space flight on development sho uld include studies of sperm function and fertilization.