Fig. 2

The Brn3c:mGFP transgenic line reveals the architecture of the retinotectal projection. (A-C) Lateral view of the retinofugal projection in a 6 dpf fixed larva, whose eye has been removed (projection of a confocal z-stack). Specimen was only lightly fixed to preserve GFP label. (A) Brn3c:mGFP transgene expression. Four arborization fields, AF-6, AF-7, AF-8 and tectum (AF-10), are visible, as well as neuromasts of the lateral line. (B) Retinofugal projection, labeled with DiI following intraocular injection. (C) Merged view of the two labels shown in A and B. (D) Transverse section of 7 dpf Brn3c:mGFP transgenic larva, showing AF-7, AF-8 and the tectal layers. (E-G) Optical sections of tecta in 6 dpf live larvae (dorsal view; anterior is upwards, midline is towards the right). (E) Shh:GFP labels all four retinorecipient layers in the tectum. (F) Brn3c:mGFP labels the SO and SFGS. (G) Double-labeling in vivo with DiI and Brn3c:mGFP, showing the absence of GFP in one of the three SFGS sublaminae. For technical reasons, live DiI staining is always incomplete. As a result, some GFP-only (green) fibers are seen in the SFGS. (H) Summary of the Brn3c:mGFP labeling pattern. RGCs project to ten AFs. The largest AF, the tectum, has four layers. Only the green areas receive significant Brn3c:mGFP input. Red areas are devoid of GFP label. Yellow area (SO) is innervated mainly by non-GFP fibers, but also receives weak Brn3:mGFP innervation. AF, arborization field; SO, stratum opticum; SFGS, stratum fibrosum et griseum superficiale; SGC, stratum griseum centrale; SAC, stratum album centrale; SPV, stratum periventriculare; asterisks, melanophores in the skin. Scale bars: 50 µm in A-D; 20 µm in E-G.