Fig. 2. Development of PAX2-positive RF and IB4-positive hyaloid artery precursors is impaired in Bmp7^-/- embryos. (A-P) Parasagittal sections at different distoproximal levels of E10.5 (A-F) or E12.5 (G-P) optic cup from wild-type or microphthamic Bmp7^-/- embryos stained with antibodies against PAX2 or with the isolectin B4 (IB4) as indicated. At E10.5, PAX2-positive staining is progressively reduced along the distoproximal axis (arrows in D-F), and by E12.5 is completely absent from the optic cup (arrows, J-L) of Bmp7 null embryos. PAX2-positive RF precursors are absent from the prospective ventral neural retina in the proximal optic cup from Bmp7-null embryos (empty arrows in E,K) when compared with the wild type (arrow in B,H). The ventral invagination of PAX2-positive precursors is nearly absent in the proximal optic cup of the mutants (empty arrow in F,L) when compared with the wild type (arrow in C,I). By contrast, PAX2-positive precursors are normally aligned on the wall of the optic stalk in both wild-type and mutant embryos (insets in I and L), although the stalk is smaller in the latter. Staining with the IB4 highlights the presence of hyaloid artery precursors in wild-type (arrow in N) but not in mutant (arrow in P) embryos, while IB4-positive vessels are visible in the distal optic cup in both wild type (M) and mutants (arrow in O). (Q) Schematic drawing summarising the morphological alterations observed in the mutant optic cup. In the mutant, ventral RF precursors are diminished and do not invaginate into the ventral optic cup. pnr, prospective neural retina; prpe, prospective retina pigmented epithelium; rfp, RF precursors. Scale bar: 50 µm in A,B,D,E; 25 µm in C,F;100 µm in G-P.