Fig. 3. OD precursors, characterised by the combined expression of Pax2, Vax1, Raldh3 and netrin 1 are absent in Bmp7-null embryos. Frontal sections of the optic cup from wild-type (A,C,E,G) and Bmp7-null (B,D,F,H) E12.5 embryos were immunostained with antibodies against PAX2 (A,B) or hybridised with specific probes for netrin 1 (C,D), Raldh3 (E,F) and Vax1 (G,H). Arrowheads in A,C,E,G indicate labelled OD precursors in wild-type optic cup. No stained precursors are observed in corresponding sections from mutant embryos. However, staining in the optic stalk (arrows in B,D,H) or ventral retina (arrow in F) precursors is observed in mutants as in wild type (arrows A,C,E,G). (I) The schematic drawing summarises the expression of the different markers shown above for E10.5 (left) and E12.5 (right) optic cups. The top drawings represent PAX2 expression in parasagittal sections at different proximodistal levels (as indicated) of the cup. The overlap between the different markers demarcates the OD. Scale bar: 50 µm