Authors: Niculescu Vladimir F
Entamoebae are anaerobe pathogenic eukaryotes capable of asymmetric cell division, self renewal, mitotic cell cycle arrest and differentiation. Key regulator of amoebic growth and differentiation is the ambient oxygen. Host’s intestine and oxygen consuming cultures (OCB cultures) are low oxygen micro-environments favouring Entamoeba’s asymmetric cell fate. In contrast, axenic cultures and extraintestinal oxygen pressure favour symmetric cell fate, identical progeny and logarithmic growth. In OCB cultures one of both daughter cells is the self-renewing cell and the other enters a state of G1 arrest (G0 quiescence) or differentiates terminally forming a tetranucleated cyst. Quiescent G0 cells have dual potential for proliferation and differentiation similar to the cycling cells prior RP commitment. Entry, maintenance and exit of quiescence are controlled by a network of intrinsic mechanisms including oxygen sensing and oxygen signalling pathways. Strong hypoxic conditions near anoxia abolish asymmetric cell division and asymmetric cell fate; the progeny consisting of identical daughter cells (ISH cells) arrest at the G2 check point. This post replicative state of quiescence is temporarily. Hypoxia decrease leads ISH cells back into asymmetric proliferation. Increased oxygen pressure as occurring in upper intestinal gradient zones (≤ 5.5% O2) favours terminal differentiation. Oxygen contents above 5.5% as occurring in axenic cultures replace asymmetric by symmetric cell division.
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