Fig. 3

Primary cilia first appear in RGC neuroblasts during apical process retraction and in an apical position. a-b Blastomeres from double transgenic embryos (atoh7:gap-RFP/Arl13b-GFP) were transplanted into wild type hosts. The resulting embryos were imaged through time-lapse confocal microscopy from around 30 hpf onwards. Montages from 3D maximum intensity projections of the stacks are shown. a A progenitor is shown, which loses its primary cilium (arrowhead) at t = 4.00 h, previous to entering M phase. b Neuroblast imaged throughout apical process retraction. The full arrowhead denotes the presence and position of the primary cilium, while the double arrowhead denotes the apical tip of the retracting process and the empty arrowhead the region of axonal outgrowth. c Plot of the relative apico-basal position of the neuroepithelium in which primary cilia first appear during the retraction of the apical process. The final position occupied by the neuroblast cell bodies (grey dashed line) and the median value of the data (black line) are also shown. d Plot of the individual values and median time-delay (black line) between the initiation of apical retraction and primary cilia appearance. e TEM micrograph from a 35 hpf embryo, showing a primary cilium at the apical tip of a retracting process. The white arrowhead indicates the basal body. RPE: retinal pigment epithelium. Time is shown in hrs:min. Scale bars: A-B, 10 µm; E, 1 µm