Expression of tubulin polyglycylation in Giardia lamblia

By means of immunofluorescence, immunoelectron microscopy and immunoblottin g, we show that polyglycylation, a posttranslational modification of tubuli n widely spread among eukaryotes, is present in the diplomonad, Giardia lam blia, a putative ancestral cell possessing a highly developed microtubular cytoskeleton. This modification was recently discovered in the ciliated pro tist, Paramecium, and was not found in the Euglenozoa, a lineage considered as ancient. We used two monoclonal antibodies (mAbs), TAP 952 and AXO 49, specifically recognizing mono- and polyglycylated tubulin isoforms, to dete ct this modification in Giardia extracts and to localize it in the differen t classes of microtubules within the cell. The alpha- and beta tubulin subu nits were recognized by the two mAbs, indicating that both tubulin subunits are glycylated, in agreement with lately reported mass spectrometry result s. Noticeably, Giardia tubulin was much more reactive with AXO 49 than with TAP 952. In situ, AXO 49 intensely labeled the microtubules present in the four pairs of flagella and the median body, and lightly decorated the micr otubules from the adhesive disc. Ln contrast, TAP 952 intensely labeled onl y the microtubules of the median body. The results indicate a differential expression of glycylated isoforms within various microtubular structures of Giardia lamblia. They also suggest that the complete set of enzymes requir ed for polyglycylation is expressed in very divergent eukaryotes. (C) Editi ons scientifiques et medicales Elsevier SAS.