Fig. 5. Sphingosine kinase 1 mRNA expression in the developing optic pathway. (A) Schematic diagram of a stage 40 Xenopus brain showing the optic pathway followed by retinal axons leaving the eye. OC, optic chiasm; Tel, telencephalon; Di, diencephalon; Tec, tectum. (B,C) Lateral views of stage 40 Xenopus brains, showing SphK1 mRNA expression alone (B) or together with retinal ganglion cell (RGC) axons visualized by HRP (brown, C). The dashed line qualitatively demarcates the anterior tectal border. (D,E) Transverse sections (60 µm) through the diencephalon and tectum of a stage 40 embryo showing SphK1 mRNA expression (B, blue) and RGC axons. Cells surrounding the migratory route of RGC axons are intensively labelled (dashed white box, D). (E) High magnification of D. SphK1 mRNA signal is absent in axon tracts (dashed white line and arrow). Ve, ventricle. Scale bars: in B, 100 µm for B,C; in D, 100 µm; in E, 50 µm.