A change in the premitotic period of the cell cycle is associated with bradyzoite differentiation in Toxoplasma gondii.
We have demonstrated that bradyzoites return to the tissue-cyst stage by a developmental pathway that is indistinguishable from that initiated by sporozoites. Mature bradyzoites, like sporozoites from oocysts, were non-proliferative as they contained uniform 1N DNA contents, and replication occurred only in parasites that de-differentiated back into tachyzoites. Moreover, tachyzoites emergent from the bradyzoite-initiated pathway underwent a spontaneous growth shift prior to the onset of tissue cyst formation in a timeframe that was identical to cultures infected with sporozoites. In sporozoite-infected cultures, a novel premitotic, near-diploid subpopulation was detected during bradyzoite differentiation that co-expressed tachyzoite and bradyzoite markers. These observations suggest that activation of a G2-related cell cycle mechanism is required during bradyzoite development, and indicates that equivalent cell cycle mechanisms may govern development in the intermediate life cycle regardless of the origin of infection.
D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle; D002454:Cell Differentiation; D005434:Flow Cytometry; D016195:G2 Phase; D018507:Gene Expression Regulation, Developmental; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008938:Mitosis; D033661:Oocysts / Q000254:growth & development / Q000502:physiology; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase; D014122:Toxoplasma / Q000166:cytology* / Q000235:genetics / Q000254:growth & development*
D000953:Antigens, Protozoan; C106179:BAG1 protein, Toxoplasma; D006360:Heat-Shock Proteins; D015800:Protozoan Proteins; C047168:SAG1 antigen, Toxoplasma