The nuclei of Giardia lamblia--new ultrastructural observations.

Giardia lamblia is a parasite possessing a complex cytoskeleton and an unusual morphology of bearing two nuclei. Here, the interphasic nuclei of trophozoites, using field emission scanning electron microscopy, routine scanning and transmission electron microscopy, immunocytochemistry, and 3D reconstruction, are presented. An approach using plasma-membrane extraction allowed the observation of the two nuclei still attached in their original positions. The observations are as follows: (1) Giardia nuclei and cytoskeleton were studied in demembranated cells by routine scanning electron microscopy and field emission; (2) both nuclei are anchored to basal bodies of the anterior flagella and to the descending posterior-lateral and ventral flagella, at the right and left nuclei, respectively, in cells attached by its ventral disc; (3) this attachment occurs by proteinaceous links, which were labeled by anti-actin and anti-centrin but not by anti-dynein or anti-tubulin antibodies; (4) fibrilar connections between the nuclei and the disc were also observed; and (5) nuclei exhibited a pendular movement when living cells were treated with cytochalasin, although the nuclei were still connected by their anterior region. Our analysis indicated that the nuclei have a defined position, and fibrils perform an anchoring system. This raises the possibility of a mechanism for nuclei-fidelity migration during mitosis.