Fig. 10

Genetic effect of FGF inhibition via SU5402 treatment (4 × 50 µM) on caudal denticle development. There was a reduction in staining intensity of bmp4 (a–bi), dlx2 (c–di), fgf3 (e–fi), fgf8 (g–hi) and shh (i–ji) in SU5402-treated specimens compared to DMSO-treated controls. We propose this resulted from the interruptions to the following GRN interactions. SU5402 inhibits FGF activity by blocking FGFR activity, thereby reducing expression of fgf3 and fgf8 (e–hi). This reduced shh and dlx2 expression as a FGF—shh positive feedback loops that would normally promote shh and dlx2 expression (as observed during feather development) were interrupted (i–ji, c–di) [78]. The fgf4–shh positive feedback loop that promotes bmp4 was also interrupted by the SU5402 treatment, reducing shh and bmp4 expression (i–ji, a–bi) [36]. SU5402-treated and DMSO control specimens both underwent the colour reaction of the WMISH protocol for the same length of time. The dashed lines show where the section was taken from. Scale bars for WMISH are 200 µm in length, and for the WMISH sections they are 100 µm in length