Delinking of S phase and cytokinesis in the protozoan parasite Entamoeba histolytica

Abstract

SummaryThe alternation of DNA replication in S phase and chromosome segregation in M phase is a hallmark in the cell cycle of most well-studied eukaryotes and ensures that the progeny do not have more than the normal complement of genes and chromosomes. An exception to this rule has been described in cancer cells that occasionally become polyploid as a result of failure to restrain S phase despite the failure to undergo complete mitosis. Here, we describe the cell division cycle of the human pathogen, Entamoeba histolytica, which routinely accumulates polyploid cells. We have studied DNA synthesis in freshly subcultured cells and show that, unlike most eukaryotes, Entamoeba cells reduplicate their genome several times before cell division occurs. Furthermore, polyploidy may occur without nuclear division so that single nuclei may contain 1-10 times or more genome contents. Multinucleated cells may also accumulate several genome contents in each nuclei of one cell. Thus, checkpoints that normally prevent DNA reduplication until after cytokinesis in most eukaryotes are not observed in E. histolytica.

Entamoeba histolytica Encodes Unique Formins, a Subset of Which Regulates DNA Content and Cell Division

“…Our previous studies have shown that an increased population of cells with 4ϫ or more genome contents identified by flow cytometry could be due to an increase in the number of multinucleated cells or in the number of genome copies in uninucleated cells (12,13,18). An increase in the number of multinucleated cells signifies a delay in cytokinesis, while an increase in the DNA content of individual nuclei suggests Increased expression of Ehformin-1 and -2 delays both cell division and mitosis.…”

“…Log-phase cultures may accumulate multinucleated cells containing heterogeneous amounts of DNA (12,18). Our previous observations suggest that genome reduplication without mitosis and irregularity in cytokinesis contribute maximally to the observed heterogeneity (12,36).…”

Entamoeba histolytica EhDEAD1 is a conserved DEAD-box RNA helicase with ATPase and ATP-dependent RNA unwinding activities

“…EhDead1 mRNA is over expressed in S phase of cell cycle EhDEAD1 exhibits 70% homology to yeast DED1 RNA helicase (Table 1), which participates in cell cycle regulation (Warbrick and Glover, 1994;Forbes et al, 1998;Grallert et al, 2000). Although axenic cultures of E. histolytica are made of a heterogeneous population of cells with varying DNA content, various studies have described cell cycle phases in log phase cultures in distinct strains or clones (Orozco et al, 1988;Dvorak et al, 1995;Gangopadhyay et al, 1997;Vohra et al, 1998;Das and Lohia 2002;Dastidar et al, 2007). Here, we used trophozoites of clone L6, which is routinely synchronized by the mitotic blocker colchicine in our laboratory and whose cell cycle phases lasting is well characterized (Orozco et al, 1988;Marchat et al, 2003).…”

Genome Re-duplication and Irregular Segregation Occur During the Cell Cycle of Entamoeba histolytica

“…Similar distribution was observed in bi-and tri-nucleated cells (quantitative data not available). Genome content of individual nuclei was estimated by DAPI fluorescence in a scanning cytometer and data from 2000 nuclei was normalized (Adapted from Das and Lohia 2002). Average distribution (%) of genome content in uni-nucleated cells was calculated from more than three independent sets of experiments.…”

“…3 Heterogeneity of genome content in E. histolytica trophozoites during vegetative growth. This cartoon is summarized from observations presented in Gangopadhyay et al (1997a), Das and Lohia (2002) and Dastidar et al (2007). Majority of cells in log phase of growth are euploid with single nucleus containing 1x-2x genome contents (A).…”