Mammalian cells are not synchronized in G1-phase by starvation or inhibition: considerations of the fundamental concept of G1-phase synchronization.

Synchronization of mammalian cells by starvation-refeeding or by inhibition-release are among the most commonly used techniques for division cycle analysis. An alternative analysis--in the form of a Gedanken or thought experiment--is presented, casting doubt on the utility of this synchronization method. Arresting cell growth produces a culture where all cells contain a G1 amount of DNA. However, these cells are not arrested at a particular point in the G1-phase. Analysis of 'G1 arrested cells' suggests that, upon resumption of growth, the cells are not synchronized.