Fig. 1

BC Axons Overshoot and Retract to Colonize the Nascent IPL

(A) Schematic showing the general organization of the vertebrate retina, including the neuropil layers, the IPL and OPL, and the retinal neurons and glia that will synapse within them.

(B) An individual BC labeled by MAZe;UAS:mYFP transgenes. The distal process extends to the basal surface (dashed line) of the retina. Branching into the IPL region can be seen, and the distal portion of the axon retracts to this point (arrow). At the same time, the apical process is also retracted from the apical surface of the retina.

(C) Transplantation scheme to create mosaic retinas with clones of vsx1:GFP-expressing BCs and ptf1a:DsRed-expressing ACs in an unlabeled host retina. At the onset of imaging, ptf1a:DsRed-expressing ACs and HCs have migrated to the AC layer. However, a separation between the dACs and ACs is not apparent. Over time, the BC axons appear (arrows) and begin to stratify in between the ptf1a:DsRed-expressing cells. As these BC axons elaborate, the ACs are separated into displaced and nondisplaced populations that are parted by the expanding IPL. Images are confocal reconstructions.

(D) Transplantation scheme to create mosaic embryos with vsx1:GFP-expressing BCs in a host retina where RGCs and ACs are labeled by ath5:GAP-RFP. BC axons (arrows) accumulate coincidentally with the appearance of the IPL, as shown by ath5:GAP-RFP-labeled RGCs and ACs (dashed line). Images represent maximum intensity projections of nine confocal slices. Time shown in hr:min. Imaging begins at ∼40 hpf. Scale bars = 10 μm. GCL, ganglion cell layer; INL, inner nuclear layer; NFL, neurofiber layer; OLM, outer limiting membrane; ONL, outer nuclear layer.

See also Figure S1 and Movies S1, S2, and S3.