Probing protistan phylogenies with an anti-tubulin antibody

Ciliary heterogeneity within a single cell: the Paramecium model

Paramecium is a single cell able to divide in its morphologically differentiated stage that has many cilia anchored at its cell surface. Many thousands of cilia are thus assembled in a short period of time during division to duplicate the cell pattern while the cell continues swimming. Most, but not all, of these sensory cilia are motile and involved in two main functions: prey capture and cell locomotion. These cilia display heterogeneity, both in their length and their biochemical properties. Thanks to these properties, as well as to the availability of many postgenomic tools and the possibility to follow the regrowth of cilia after deciliation, Paramecium offers a nice opportunity to study the assembly of the cilia, as well as the genesis of their diversity within a single cell. In this paper, after a brief survey of Paramecium morphology and cilia properties, we describe the tools and the protocols currently used for immunofluorescence, transmission electron microscopy, and ultrastructural immunocytochemistry to analyze cilia, with special recommendations to overcome the problem raised by cilium diversity.

Tubulins in Trichomonas vaginalis: molecular characterization of alpha-tubulin genes, posttranslational modifications, and homology modeling of the tubulin dimer

We have isolated and analysed an alpha-tubulin-encoding gene (atub1) in an early-diverging eukaryote, Trichomonas vaginalis. The complete atub1 open reading frame included 1.356 bp encoding a polypeptide of 452 amino-acyl residues. A second alpha-tubulin gene (atub2) was amplified by PCR using primers derived from consensus alpha-tubulin amino acid sequences. Both T. vaginalis alpha-tubulin sequences showed high identity to those described in other parabasalids (94.4%-97.3%), and exhibited a high degree of similarity to sequences from Metazoa (such as pig brain) and diplomonads (such as Giardia). Despite large evolutionary distances previously observed between trichomonads and mammals, the three-dimensional model of the T. vaginalis tubulin dimer was very similar to that of pig brain. Possible correlations between alpha-tubulin sequences and posttranslational modifications (PTMs) were examined. Our observations corroborated previous data obtained in T. vaginalis using specific anti-PTMs antibodies. As described in the related species Tritrichomonas mobilensis, microtubules are likely acetylated, non-tyrosinated, glutamylated, and non-glycylated in T. vaginalis. Evolutionary considerations concerning the time of appearance of these tubulin PTMs are also discussed since trichomonads are potentially one of the earliest diverging eukaryotic lineages.

Tubulin post-translational modifications in the primitive protist Trichomonas vaginalis

Using several specific monoclonal antibodies, we investigated the occurrence and distribution of different post-translationally modified tubulin during interphase and division of the primitive flagellated protist Trichomonas vaginalis. Immunoblotting and immunofluorescence experiments revealed that interphasic microtubular structures of T. vaginalis contained acetylated and glutamylated but non-tyrosinated and non-glycylated [Brugerolle and Adoutte, 1988: Bio Systems 21: 255-268] tubulin. Immunofluorescence studies performed on dividing cells showed that the extranuclear mitotic spindle (or paradesmosis) was acetylated and glutamylated, which contrast with the ephemeral nature of this structure. Newly formed short axostyles also contained acetylated and glutamylated tubulin suggesting that both post-translational modifications might take place very early after assembly of microtubular structures. Our results indicate that acetylation and glutamylation of tubulin appeared early in the history of eukaryotes and could reflect the occurrence of post-translational modifications of tubulin in the primitive eukaryotic cells. These cells probably had a highly ordered cross-linked microtubular cytoskeleton in which microtubules showed a low level of subunit exchange dynamics.

Monoclonal and polyclonal antibodies detect a new type of post-translational modification of axonemal tubulin

Polyclonal (PAT) and monoclonal (AXO 49) antibodies against Paramecium axonemal tubulin were used as probes to reveal tubulin heterogeneity. The location, the nature and the subcellular distribution of the epitopes recognized by these antibodies were, respectively, determined by means of: (i) immunoblotting on peptide maps of Paramecium, sea urchin and quail axonemal tubulins; (ii) immunoblotting on ciliate tubulin fusion peptides generated in E. coli to discriminate antibodies directed against sequential epitopes (reactive) from post-translational ones (non reactive); and (iii) immunofluorescence on Paramecium cells, using throughout an array of antibodies directed against tubulin sequences and post-translational modifications as references. AXO 49 monoclonal antibody and PAT serum were both shown to recognize epitopes located near the carboxyl-terminal end of both subunits of Paramecium axonemal tubulin, whereas the latter recognized additional epitopes in alpha-tubulin; AXO 49 and a fraction of the PAT serum proved to be unreactive over fusion proteins; both PAT and AXO 49 labelled a restricted population of very stable microtubules in Paramecium, consisting of axonemal and cortical ones, and their reactivity was sequentially detected following microtubule assembly; finally, both antibodies stained two upward spread bands in Paramecium axonemal tubulin separated by SDS-PAGE, indicating the recognition of various alpha- and beta-tubulin isoforms displaying different apparent molecular masses. These data, taken as a whole, definitely establish that PAT and AXO 49 recognize a post-translational modification occurring in axonemal microtubules of protozoa as of metazoa. This modification appears to be distinct from the previously known ones, and all the presently available evidence indicates that it corresponds to the very recently discovered polyglycylation of Paramecium axonemal alpha- and beta-tubulin.