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A more recent version of this article appeared on April 1, 2006
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Submitted on October 24, 2005
Revised on December 29, 2005
Accepted on January 26, 2006
Bernhard Nocht Institute for Tropical Medicine, Parasitology Section, D-20359 Hamburg, Germany
Monitoring Editor: J. Silvio Gutkind
A striking difference of the life stages of the protozoan parasite Leishmania is a long flagellum in the insect stage promastigotes and a rudimentary organelle in the mammalian amastigotes. LmxMKK, a MAP kinase kinase from L. mexicana, is required for growth of a full length flagellum. We identified LmxMPK3, a MAP kinase homologue, with a similar expression pattern as LmxMKK being not detectable in amastigotes, up-regulated during the differentiation to promastigotes, constantly expressed in promastigotes, and shut down during the differentiation to amastigotes. LmxMPK3 null mutants resemble the LmxMKK knockouts with flagella reduced to 1/5 of the wild type length, stumpy cell bodies, and vesicles and membrane fragments in the flagellar pocket. A constitutively activated recombinant LmxMKK activates LmxMPK3 in vitro. Moreover, LmxMKK is likely to be directly involved in the phosphorylation of LmxMPK3 in vivo. Finally, LmxMPK3 is able to phosphorylate LmxMKK indicating a possible feedback regulation. This is the first time that two interacting components of a signaling cascade have been described in Leishmania. Moreover, we set the stage for the analysis of reversible phosphorylation in flagellar morphogenesis.