Fig. 3. Incorporation of BrdU by Fgfr3-expressing cells. We labelled E18 embryos by two intra-peritoneal injections of BrdU, 6 hours apart, into the mother. We harvested the embryos 3 hours later and performed in situ hybridisation for Fgfr3 followed by immunohistochemistry for BrdU. The Fgfr3 (A) and BrdU (B) images were superimposed using Adobe Photoshop (C). Many Fgfr3-expressing cells incorporated BrdU (C, arrows), confirming that they can divide after exiting the VZ and are therefore unlikely to be neurones. Arrowheads in B,C indicate Fgfr3-negative cells that have incorporated BrdU.