I did cell synchronization by serum starvation to my cultured mammalian cells for 24 hours and I did FACS analysis, however I found no G1 arrest, I prolong the starvation for 72 hours but I got G2/M arrest. Is this reasonable?
Hello Sya Retno
No, it may not be reasonable because prolonged incubation (>48 hrs.) in serum-deprived medium may have caused damaging effects on the cells leading to G2/M arrest. The most stringent checkpoint which occurs during G2, abruptly and completely halts cell-cycle progression by imposing a delay that is linearly correlated with the amount of DNA damage. This G2 phase checkpoint which is also known as G2/M-phase checkpoint prevents cells from entering mitosis when DNA is damaged, providing an opportunity for repair and stopping the proliferation of damaged cells.
There is a restriction point in the G1 phase of the mammalian cell cycle which is a unique point at which starved or inhibited cells come to rest. It regulates the entry of a cell into a new round of the cell cycle.
When cells are starved, initiation of S phase ceases, but cells complete the S and G2/M phases in progress and continue until cell division. Cells in G1 phase remain with a G1 phase amount of DNA as the cells do not initiate DNA synthesis. Cells in S and G2/M proceed through the cell cycle to divide and produce daughter cells, each with a G1 phase amount of DNA. Cessation of S phase initiations and completion of S/G2/M phases in progress leads to the accumulation of cells all with a G1 phase amount of DNA. The effects of serum starvation can be reversed by the addition of serum to media once cell synchrony has occurred.
Usually, deprivation of growth factors by serum-starvation is the most commonly used method to arrest cells in G1 phase. If your cells do not show G1 arrest even after 48hrs it simply means that the cells because of its origin may have acquired some additional growth factor independence, a characteristic which is seen in most of the cancer cells.
Which mammalian cells are you using? Is it a cancer cell line?
Best.
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