Fig. 1

Expression of netrin-1 and of its receptors DCC and UNC-5 in stage 45 Xenopus optic tectum. a Schematic of coronal section of Xenopus retinotectal circuit. RGC axons (green) travel from the contralateral eye to connect with tectal neurons in the neuropil (blue). b, c In situ hybridization with Xenopus-specific antisense netrin-1 probes. Coronal sections of the midbrain at the level of the optic tectum show ventral-high (double arrows) to dorsal-low (arrow) netrin-1 mRNA expression along the ventricle wall. d–g Coronal and h, i horizontal sections show DCC and UNC-5 expression. d–g Co-immunostaining illustrates the differential distribution of UNC-5 (red) and DCC (green) immunoreactivity. d DCC immunoreactivity (green) is localized to the cell bodies in the dorsal tectum and proximal dendrites and to incoming axons near the dorsal neuropil (arrow). The tectal neuropil (np) is also positive for DCC. The low- (e, f) and high- (g) magnification coronal images show UNC-5 (red) and DCC (green) co-localization, with UNC-5 being localized to a subset of cells that also expresses DCC (g, arrowheads). f Counterstaining with DAPI (blue) serves to distinguish nuclear staining from cytoplasmic UNC-5 (red) and DCC (green) expression in tectal cells. h UNC-5 immunoreactivity (green) is localized to a subset of cell bodies in the dorsal area of the tectum and area adjacent to the tectal neuropil identified by immunostaining with antibodies to the presynaptic protein SNAP-25 (red). i Anterograde labeling with rhodamine dextran shows that RGC axons (red) terminate in the areas of the tectal neuropil (arrow) where UNC-5 immunopositive neurons localize (green). D dorsal, V ventral, C caudal, R rostral, L lateral, np neuropil. Scale bars: 50 μm in b–f, 20 μm in g, 20 μm in h–i