Role of serum in regulating the Entamoeba histolytica cell cycle: a flowcytometric analysis.

To identify stage-specific molecules that might be important in pathogenicity, we focused on synchronizing Entamoeba histolytica HM1:1MSS axenic cultures by serum deprivation. By growing trophozoites in medium containing 2% serum for 16 h and then replacing with complete medium, we found that most of the trophozoites were in the G0/G1 phase of the cell cycle. Subsequently, the distribution of trophozoites in G0/G1, S and G2/M phases was studied for up to 24 h and it was observed that after 8 h, the trophozoites began to come out of the quiescent G0/G1 phase and the S and G2/M populations increased, indicating that certain serum factors regulate induction of cell division. It will be important to investigate these factors to find serum substitutes for cultivation media.