Fig. 1

Hedgehog signaling down-regulates pax3/7 expression after the 19-somite stage. A clutch of smu^+/- embryos was hybridized with pax3 or pax7 probes during early embryonic stages. (A) Dorsal view of embryos at 10S and 14S stages. At the 10S stage, myoD and myf5 are expressed in adaxial cells (arrows) and the posterior part of newly formed somites. Neither pax3 nor pax7 is expressed in adaxial cells (arrows). pax3 is expressed initially throughout the non-adaxial portion of the somite; pax3 is also expressed in the neural folds (n). pax7 is not expressed in the somites. At the 14S stage, pax7 is expressed in the anterior part of somites, at this stage the somitic expression of pax3 is very similar but has much higher expression in neural tissue. (B) Lateral view of embryos at 17S stage, the expression of pax3 and pax7 continues to be strongest in the anterior part of somites, and is indistinguishable between wild-type and smu mutant embryos. (C) After the 19-somite stage, pax3 expression is down-regulated in wild-type embryos, while the segmented expression of pax3 is maintained in embryos mutant for smu(smo), at least until the end of segmentation stage (30S). pax7 expression is also down-regulated during this period in wild-type embryos, while the segmented expression of pax7 is maintained at high levels in embryos mutant for smu(smo). Scale bar = 100 μm.