THE SURFACE CONTRACTION WAVES OF XENOPUS EGGS REFLECT THE METACHRONOUS CELL-CYCLE STATE OF THE CYTOPLASM

Activated Xenopus laevis eggs undergo a series of surface contractions in response to cell-cycle progression but fail to cleave unless the s perm centrosome is present, These surface contraction waves (SCWs) beg in at the animal pole and progress around the egg, occur every cell cy cle and precede cleavage [1-3]. The SCWs are biphasic, comprising a re laxation phase (SCWa) and a contraction phase (SCWb), To investigate h ow these events are linked to the underlying cell cycle, we studied th e temporal and spatial relationship between the SCWs and previously ch aracterized biochemical markers of cell cycle progression. We found th at the relaxation phase was a response to activated maturation-promoti ng factor (MPF), In contrast, the contraction phase required inactivat ion of MPF and was blocked when MPF activity was maintained at elevate d levels, We also found that a wave of MPF activity traveled within th e cell from the animal to the vegetal hemisphere, Taken together, thes e experiments suggest that the SCWs are a local response to a wave of MPF activation and inactivation, The egg cytoplasm, therefore, is meta chronous in terms of cell-cycle progression; multiple cell-cycle state s are present and spatially distinct within the egg at the same time.