Mechanism of cell division in entamoeba histolytica

Abstract

The cell division cycle of Entamoeba histolytica shows important differences from that of unicellular and higher eukaryotes. We have observed that E. histolytica cultures are made up of a heterogeneous population of cells that contain one or many nuclei and varying DNA content in each nucleus. Chromosome segregation occurs on a variety of atypical microtubular assemblies, and daughter cells are formed from mechanical rupture of cytoplasmic extensions that may need “helper cells” to complete the separation. Our observations suggest that whole genome copies are lost when cells shift from axenic to xenic cultures or from trophozoites to cysts. Gain or loss of whole genome copies during changes in growth conditions is possibly sustained by the inherent plasticity of the amoeba genome. Molecular studies have shown that orthologues of conserved checkpoint proteins that regulate the eukaryotic cell cycle are absent in this organism. Absence of checkpoint control leads to unregulated DNA synthesis, asymmetrical chromosome segregation, and aberrant cytokinesis in eukaryotes. In spite of the perceived lack of control and atypical mode of genome multiplication and partitioning, these cells survive in a foreign host, to multiply and cause disease or remain dormant for long periods of time, followed by active growth. Absence of known regulatory mechanisms coupled to a unique form of cell division and propagation makes the events leading to formation of Entamoeba daughter cells an interesting and challenging study. This chapter summarizes our recent attempts in understanding the cell division process of Entamoeba histolytica.