Expression of RhoGAP71EScer\UAS.ORF.T:Ivir\HA1 under the control of Scer\GAL4mat.αTub67C.T:Hsim\VP16 does not disrupt the pulsatile contractions of embryonic cells and increases their maximum constriction rate. RhoGAP71EScer\UAS.ORF.T:Ivir\HA1 expression significantly increases the fraction of unratcheted pulses (relative to ratcheted and unconstricting pulse types), also prevents the gradual increase in pulse frequency observed in wild-type embryos and 'locks' the pulse frequency at an intermediate interval.