Mitotic patterns and DNA synthesis in dinitrophenol-treated sea urchin eggs

Eggs of Paracentrotus exposed to 1 mM 2,4-dinitrophenol (DNP) in sea water at 10-min intervals from 10 to 40 min after insemination and returned to normal sea water 60 min later, divide into two cells. If, however, such eggs are treated for 60 min beginning at 50 min after insemination, they cleave directly into four cells. Division centers can split and separate in the DNP solution though the asters appear very faint and the spindle considerably reduced in size. This means that DNP has an inhibitory effect on duplication of division centers but not on the splitting and separation of centers already duplicated. Cytophotometric comparison of the DNA content in di-, tri- and tetrapolar mitosis of DNP-treated and control eggs revealed no difference showing that chromosome cycle and centrosome cycle are independent events in the cell cycle.