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Fig. 4. One copy of either Gli2 or Gli3 is required for tissue
autonomous Shh responsiveness. (A) Shh expression was assessed by
whole-mount in situ hybridization at E9.5. Transverse sections through the
trunk reveal dramatically reduced Shh in the notochord and floorplate
of
Gli2/Gli3/
embryos (compare arrowheads in A). (B) PSM tissue was isolated from E9.5
wild-type, Gli3/,
Gli2/,
Gli2/Gli3+/ and
Gli2/Gli3/
embryos and cultured in the presence (+) or absence () of Shh-N for 24
hours. Induction of target genes was assessed by RT-PCR. ß-Actin serves
as a control for normalization. Compared with wild-type PSM,
Gli3/ PSM shows Shh-responsiveness with an
increase in Pax9 expression in the absence of Shh-N (n=4).
Gli2/ PSM shows reduced responsiveness in
activating Ptch and Pax9, but normal induction of other
targets (n=4). In
Gli2/Gli3+/ PSM,
all targets are induced with some reduction in Pax9 induction
(n=2). In Gli2/
Gli3/ PSM, all targets tested are expressed
identically in the presence and absence of Shh-N. There is increased basal
expression of Ptch and Pax9 in
Gli2/Gli3/
PSM independent of Shh-N (n=3).