Fig. 4. VEGFA expression correlates with formation of the PNVP. E8.5-9.5 Vegf-lacZ^+/– embryos were dissected and processed for either ß-gal or PECAM antibody staining. (A) An embryo at E8.5-9.0 with 12 somites (left), and an embryo at E9.5 with 20-25 somites (right). The lines indicate the level of transverse sections shown in B-J. (B) Posterior section through an E9.5 wild-type embryo ß-gal stained as a negative control. (C,D) Posterior sections through E8.5 Vegf-lacZ^+/– embryos stained for ß-gal (C) or PECAM (D). Note the lack of ß-gal staining in the neural tube (asterisk) and the ß-gal reactivity in the underlying endoderm in C, and the lack of vessels around the neural tube in D. (E,F) Anterior sections through E8.5 Vegf-lacZ^+/– embryos stained for ß-gal (E) or PECAM (F). Note the diffuse ß-gal reactivity in the neural tube, and the stronger signal from the underlying endoderm in E, and the partial PNVP in F. (G,H) Posterior sections through E9.5 Vegf-lacZ^+/– embryos stained for ß-gal (G) or PECAM (H). (I,J) Anterior sections through E9.5 Vegf-lacZ^+/– embryos stained for ß-gal (I) or PECAM (J). Note the stronger ß-gal reactivity that is partially localized to the lateral edge of the neural tube in I, and the fully formed PNVP in J. Asterisks indicate the central canal of the neural tube in B-J. Scale bars: 50 µm in B-H; 100 µm in I,J. A is reproduced, with permission, from Kaufman (Kaufman, 1992).