Microgravity alters protein phosphorylation changes during initiation of sea urchin sperm motility

European Space Agency (ESA) studies demonstrated that bull sperm swim with higher velocity in microgravity (mu G) than at 1 G, Coupling between protei n phosphorylation and sperm motility during activation in mu G and at 1 G w as examined in the ESA Biorack on two space shuttle missions. Immotile sper m were activated to swim (86-90% motility) at launch +20 h by dilution into artificial seawater (ASW), Parallel ground controls were performed 2 h aft er the flight experiment. Activation after 0, 30, and 60 s was terminated w ith electrophoresis sample buffer and samples analyzed for phosphoamino aci ds by Western blotting. Phosphorylation of a 130-kDa phosphothreonine-conta ining protein (FP130) occurred three to four times faster in mu C than at 1 G, A 32-kDa phosphoserine-containing protein was significantly stimulated at 30 s but returned to 1 G control levels at 60 s, The rate of FP130 phosp horylation in mu G was attenuated by D2O, suggesting that changes in water properties participate in altering signal transduction, Changes in FP130 ph osphorylation triggered by the egg peptide speract were delayed in mu G. Th ese results demonstrate that previously observed effects of mu G on sperm m otility are coupled to changes in phosphorylation of specific flagellar pro teins and that early events of sperm activation and fertilization are alter ed in mu G.