Regulation of Chlamydomonas flagella and ependymal cell motile cilia by ceramide-mediated translocation of GSK3

Cilia are important organelles formed by cell membrane protrusions; however, little is known about their regulation by membrane lipids. We characterize a novel activation mechanism for glycogen synthase kinase-3 (GSK3) by the sphingolipids phytocer-amide and ceramide that is critical for ciliogenesis in Chlamydomonas and murine ependy-mal cells, respectively. We show for the frst time that Chlamydomonas expresses serine palmitoyl transferase (SPT), the frst enzyme in (phyto)ceramide biosynthesis. Inhibition of SPT in Chlamydomonas by myriocin led to loss of fagella and reduced tubulin acetylation, which was prevented by supplementation with the precursor dihydrosphingosine. Immu-nocytochemistry showed that (phyto)ceramide was colocalized with phospho-Tyr-216-GSK3 (pYGSK3) at the base and tip of Chlamydomonas fagella and motile cilia in ependy-mal cells. The (phyto)ceramide distribution was consistent with that of a bifunctional ceramide analogue UV cross-linked and visualized by click-chemistry-mediated fuorescent labeling. Ceramide depletion, by myriocin or neutral sphingomyelinase defciency (fro/fro mouse), led to GSK3 dephosphorylation and defective fagella and cilia. Motile cilia were rescued and pYGSK3 localization restored by incubation of fro/fro ependymal cells with exogenous C24:1 ceramide, which directly bound to pYGSK3. Our fndings suggest that (phyto)ceramide-mediated translocation of pYGSK into fagella and cilia is an evolution-arily conserved mechanism fundamental to the regulation of ciliogenesis.