Fig. 10. Modulation of the Pax2-positive astrocyte precursor cell population at the optic disc by Shh signaling. Optic cups of E12 (A-C) and E14 (D-H) C57BL/6 embryos were cultured for 48 hours, untreated (A,E) or treated with recombinant Shh-N (B,D,F,H) or the anti-Shh antibody 5E1 (C,G), and sectioned for in situ hybridization for Pax2 (A-G) and Gli (H) expression. Compared with control (A), the size of the Pax2-positive cell population at the optic disc was markedly increased by Shh-N treatment (B), whereas 5E1 treatment (C) resulted in an almost complete loss of these cells. (D,H) The kinetics of Hh responsiveness by optic disc cells is maintained in vitro, as the Pax2-positive cells (arrow in D) of the E14 Shh-N treated explants downregulate Gli (arrow in H) expression by the second day in culture. Consistent with this observation, the size of the Pax2-positive cell population at the optic disc did not differ much between controls (E) and Shh-N treated (F) cultures, but was much reduced in the 5E1 (G) treated explants at E14.

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