Fig. S1

Eye development proceeds normally in bum^-/- embryos until 2 dpf. (A–D) Toluidine blue-stained transversal semi-thin sections through the central part of the eyes of 36 hpf (A, B) and 2 dpf (C, D) bum^-/- mutant embryos. A and C show cross-sections of entire heads, B and D shows higher magnifications of individual eyes. (E, F) Thin-section electron microscopy images of transversal sections through the central part of the lens of 2 dpf bum^-/- zebrafish larvae: overview (E) and higher magnification of the lens’ bow region (F) comprising the early differentiating secondary lens fibre cells. These images demonstrate that the hyperproliferation of the anterior lens epithelium and the degenerative changes in the secondary lens fibre cells observed in bum^-/- mutant larvae at later developmental stages are not apparent at these earlier stages. Brackets in panels B and D–F indicate the monolayer of anterior lens epithelial cells. The overall morphology of the head (A, C) and eye (B, D), including the development of the neural retina are also normal in bum^-/- mutant larvae. Abbreviations: C, cornea; L, lens; LE, lens epithelium; n, elongated nuclei of the differentiating secondary lens fibre cells; NR, neural retina; ON, optic nerve leaving the eye; PFC, primary lens fibre cells; SFC, secondary lens fibre cells.