Entamoeba histolytica: cell cycle and nuclear division.

The cell cycle of Entamoeba histolytica, the duration of its phases, and the details of the nuclear division stages are described in this paper. Trophozoites from clone L-6, strain HM1:IMSS, were synchronized by colchicine. Synchrony was observed immediately after treatment and cultures remained synchronous for at least three replicative cycles with synchrony indexes between 13 and 15 hr. The stages of nuclear division were studied by light and electron microscopy. Four stages of the nuclear division were defined: prophase, early anaphase, late anaphase, and telophase. No metaphase stage was observed by light or electron microscopy. One of the first events in the nuclear division was the presence of a bud close to the juxtanuclear body, which grew to a daughter nucleus. The karyosome and the nuclear membrane remained throughout the mitotic process. Bundles of intranuclear microtubules were observed forming a "V" from the center of the nucleus to one of the poles, and associated with them, 12 to 16 chromosomes-like structures appeared. The results of these studies strongly suggest that division of E. histolytica involved a pleuromitotic process which is carried out in about 120 min.