BACKGROUND: Motile cilia are essential to the survival and reproduction of many eukaryotes; they are responsible for powering swimming of protists and small multicellular organisms and drive fluids across respiratory and reproductive surfaces in mammals. Although tremendous progress has been made to comprehend the biochemical basis of these complex evolutionarily-conserved organelles, few protein kinases have been reported to co-ordinate ciliary beat. Here we present evidence for p38 mitogen-activated protein kinase (p38 MAPK) playing a role in the ciliary beat of a multicellular eukaryote, the free-living miracidium stage of the platyhelminth parasite Schistosoma mansoni.\ud \ud RESULTS: Fluorescence confocal microscopy revealed that non-motile miracidia trapped within eggs prior to hatching displayed phosphorylated (activated) p38 MAPK associated with their ciliated surface. In contrast, freshly-hatched, rapidly swimming, miracidia lacked phosphorylated p38 MAPK. Western blotting and immunocytochemistry demonstrated that treatment of miracidia with the p38 MAPK activator anisomycin resulted in a rapid, sustained, activation of p38 MAPK, which was primarily localized to the cilia associated with the ciliated epidermal plates, and the tegument. Freshly-hatched miracidia possessed swim velocities between 2.17 - 2.38 mm/s. Strikingly, anisomycin-mediated p38 MAPK activation rapidly attenuated swimming, reducing swim velocities by 55% after 15 min and 99% after 60 min. In contrast, SB 203580, a p38 MAPK inhibitor, increased swim velocity by up to 15% over this duration. Finally, by inhibiting swimming, p38 MAPK activation resulted in early release of ciliated epidermal plates from the miracidium thus accelerating development to the post-miracidium larval stage.\ud \ud CONCLUSIONS: This study supports a role for p38 MAPK in the regulation of ciliary-beat. Given the evolutionary conservation of signalling processes and cilia structure, we hypothesize that p38 MAPK may regulate ciliary beat and beat-frequency in a variety of eukaryotes
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