Development of the tracheal system from stage 15 to stage 16 of embryogenesis. DB migrates toward dorsal midline and fuses with its counterpart that comes from contralateral hemisegment. Note that the diameter of DB becomes smaller and is accompanied by cell rearrangement. Numerous floating cells are also observed. They are likely to be the cells that have failed to remain in the tracheal epithelium. For this and other movies, tracheal cells are labeled with GFP-moesin expressed by the btl enhancer. Elapsed time is shown at the top right-hand corner. Anterior is towards the left. and dorsal is upwards.

Effect of reduced Rac activity on dorsal branch migration. DRac1N17 was overexpressed by the btl enhancer. Although cells at the tip extend numerous cell extensions, they fail to reach the dorsal midline. The stalk of DB is thinner and contains fewer cells compared with the control.

Close up of view of DRac1V12 phenotype. While apicobasal polarity is becoming lost, as can be seen by the abnormal accumulation of GFP-moesin inside of dorsal branch, numerous cells become rounded and dissociated.