Figure 7.

The effect of T4 on skeletogenesis is inhibited by PD98059, an ERK1/2 inhibitor but not p38 inhibitor. (A) Gastrulae were pre-exposed to PD98059 before being exposed to T4 for 20 h (n = 100). Following exposure, spicule initiation was monitored hourly for 5 h. The hypothesis that PD98059 inhibits the effect of T4 on skeletogenesis was tested using a binary logistic regression (D = 232, df = 110). T4 increased the rate of skeletogenesis, while PD98059 inhibited the effect of T4 on skeletogenesis (Bonferroni corrected p <0.0001). The highest levels of PD prevented skeletogenesis completely, an effect which was rescued by T4 (Bonferroni corrected p = 0.0012). This suggests that T4 acts through a MAPK (ERK1/2) cascade. (B) Gastrulae were pre-exposed to SB203580 before being exposed to T4 for 20 h (n = 20). Following exposure, spicule proportion at 41 hpf was observed. The hypothesis that SB inhibits skeletogenesis was tested using a binary logistic regression (D = 11, df = 12). T4 increased the rate of skeletogenesis (Bonferonni corrected p < 0.001), while SB had neither a significant effect on skeletogenesis nor any interaction with the effect of T4 (p = 0.996).