Tubulin polyglycylation: a morphogenetic marker in ciliates

The occurrence of the tubulin post-translational modification, polyglycylat ion, in stable microtubular structures was investigated during morphogenesi s in two ciliates, Paramecium and Frontonia atra, belonging to the Epiplasm ata group. This analysis was carried out by means of immunofluorescence and postembedding immunoelectron microscopy using two monoclonal antibodies, T AP 952 and AXO 49, respectively recognizing mono- and polyglycylated sites in alpha- and beta -tubulin. In the course of cell division, the TAP 952 ep itope is detected in all microtubular structures including the newly assemb led ones, such as cortical and oral basal bodies and cilia. In contrast, th e AXO 49 epitope is only present in 'old' microtubular structures such as p arental cortical and oral basal bodies and cilia. Our observations show tha t, in ciliates: 1) this tubulin post-translational modification takes place early in the course of morphogenesis; and 2) the lengthening of the polygl ycine chains occurs after a great delay following addition of the first gly cine residues on the tubulin glycylation sites, and following microtubule a ssembly. Thus, a sequential mechanism of polyglycylation is shown to take p lace in the tubulin molecule and during morphogenesis in Paramecium and Fro ntonia atra. Accordingly, polyglycylation, through a time-dependent polygly cine chain elongation process, appears to be a morphogenetic marker in cili ates. (C) 2000 Editions scientifiques et medicales Elsevier SAS.