Participation of the adhesive disc during karyokinesis in Giardia lamblia.

Evidence is presented for a potential involvement of the adhesive disc on the nucleus division in Giardia lamblia. The trophozoite mitotic nucleus was studied by transmission electron microscopy, freeze-fracture, freeze-substitution and also by immunofluorescence microscopy using anti-tubulin antibodies specific to spindle microtubules and Panotic staining. Prior to cell division the nucleus elongated and a displaced disc fragment, established contact with the nucleus. A progressive nucleus indentation was coincident with the concomitant presence of a disc fragment at the constricted region. One nucleus each time progressively divided until the karyokinesis was finished and two daughter-nuclei were observed. After the first karyokinesis a second karyokinesis takes place following the same procedure. When Giardia gets the four nuclei, cytokinesis occurs. Duplicated basal bodies were seen in between the first and the second karyokinesis. Immunofluorescence microscopy, using a panel of anti-tubulin antibodies, and electron microscopy of cells processed using microtubule stabilizer buffers, or cells fast-frozen and freeze-substituted, did not reveal the presence of a typical spindle. We propose that Giardia lamblia presents an uncommon mitotic behavior where the adhesive disc, a microtubular structure, seems to participate in the karyokinesis process.