"Surface Contraction Waves" have been described in eggs of a number of amphibian species at the end of the first and subsequent cell cycles. In each cell cycle, a first wave (SCW-1) occurs at the time of mitosis and is in fact a wave of cortical relaxation. SCW-2 is a true cortical contraction associated with the rounding up of the egg and cleavage furrow formation.

In Xenopus (Movies : 430 Kb and 17.6Mb) , labelling of subcortical mitochondrial islands using a vital dyes allows clear visualisation of SCW-1 and to a lesser extent SCW-2.The movement in the first cell cycle is atypical, sweeping across the vegetal pole region. In subsequent cycles the waves terminate at the vegetal pole (Pérez-Mongiovi et al, 1998). The SCWs thus contribute to the progressive concentration of the germ plasm at the vegetal pole of the embryo.

In Beroe (Movie : 750 Kb) eggs, waves similar to the SCWs travel across the egg starting from the site of the zygote nucleus prior to first cleavage. A microtubule-dependent cytoplasmic reorganisation, apparent as the dispersal of accummulated fluorescence around suppernumerary sperm These correlate spatially and temporally with the establishment of the unique embryonic axis, although no functional link with axis specification has been demonstrated (Houliston et al, 1993).

We have shown that SCW-1 in Xenopus is driven by localised activation of MPF, the universal mitotic kinase. MPF activation is triggered in the animal half of the egg and then propagates to the vegetal pole, probably involving the reciprocal activation of Cdc2 and Cdc25 by dephosphorylation/phosphorylation (Pérez-Mongiovi et al, 1998).
Ectopic waves (Movie : 900 Ko) resembling SCW-1 can be provoked by localised micro-injection of MPF.

Studies in egg fragments and in cytoplasmic extracts show that nuclei and the centrosomes can stimulate MPF activation (Pérez-Mongiovi et al, 2000). This suggests that the endogenous MPF activation wave is initiated in association with the animal-located nucleus/centrosome complex

Fractionation of Xenopus egg cytoplasm , along with imaging of cyclinB, has shown that nuclear envelope structures asscoiate with MPF, and are contained in a fraction that stimulates MPF activation (Beckhelling et al, 2003)