Fig. 8. Anterior identity confers neurogenic potential in the FP cells. Otx2 (A) or Mash1 (B) are ectopically expressed under the control of the FP-specific enhancer of the Shh gene. Images show the ventral midline region of the metencephalon at E11.5 (A) or at E12.5 (B). The transgene is selectively expressed in the cFP region. In Otx2-transgenic embryos, cFP cells acquire mesFP-like characteristics and mesDA neurogenesis occurs in the cFP region. By contrast, in Mash1-transgenic embryos, cFP cells differentiate into neurons positive for Th and Lmx1b, but negative for other mesDA markers.