THE GELSOLIN-RELATED FLIGHTLESS-I PROTEIN IS REQUIRED FOR ACTIN DISTRIBUTION DURING CELLULARISATION IN DROSOPHILA

We have analysed the developmental defects in Drosophila embryos lacki ng a gelsolin-related protein encoded by the gene flightless I. Such e mbryos have previously been reported to gastrulate abnormally, We now show that the most dramatic defects are seen earlier, in actin-depende nt events during cellularisation of the syncytial blastoderm, a proces s with similarities to cytokinesis, The blastoderm nuclei migrate to t he periphery of the egg normally but lose their precise cortical posit ioning during cellularisation. Cleavage membranes are initially formed , but invaginate irregularly and often fail to close at the basal end of the newly formed cells. The association of actin with the cellulari sation membranes is irregular, suggesting a role for flightless I in t he delivery of actin to the actin network, or in its stabilisation.