The plasmodia of Physarum polycephalum, an elegant system to demonstrate the importance of genome integrity in traversing the G2/M checkpoint of the cell cycle

In this communication we show the usefulness of the plasmodia of Physarum p olycephalum to demonstrate important concepts in cell cycle regulation, suc h as the need for an undamaged chromosomal DNA to allow the transition from late G2 to prophase (G2/M checkpoint). In Physarum,, chromosomal DNA synth esis is confined approximately to the first one-third of the cell cycle whi ch comprises the S phase, and rDNA and mitochondrial DNA are synthesized th roughout the cycle except during mitosis and early S phase. Taking advantag e of these facts, DNA of the plasmodia was substituted with 5-bromo-2'-deox yuridine at a concentration where it had no effect on DNA synthesis per se during different phases of the cell cycle before exposure to UV during late G2, A strong synergistic effect between BrdU and UV, in terms of mitotic d elay, was observed only in plasmodia treated with the base analogue during the early S phase, thereby showing that the integrity of chromosomal DNA is an important prerequisite for the initiation of mitosis, It is suggested t hat this system is ideal for molecular level studies on this aspect of chec kpoint operation.