Fig. 5

Small molecules perturb segmentation at distinct steps. Wild type embryos after in situ hybridization for xirp2a mRNA at 36 hpf to mark myotome boundaries a–c, j–l, her7 mRNA at 10 ss to show segmentation clock expression d–f, and live at 12 ss to show somite boundaries, N = 3 g–i, treatments as indicated. a 0.5% DMSO-treated control embryos. b 3 µM SB225002 treatment from tailbud (tb), myotome boundary defects of the mid-trunk, segments 3–15 (brackets, inset). c 2 µM XRP44X, segment defects along axis (brackets), ectopic staining of xirp2a within myotomes (inset). d-f Cyclic her7 mRNA normal in all treatments. Blue outline indicates PSM, broken lines indicate area of formed somites, (n = 45, 3 of 3 experiments). g 0.5% DMSO and i 2 µM XRP44X showed normal somite formation with intact formed somite boundaries (arrows). h 3 µM SB225002, no clear somite boundaries posterior to somite 5 (arrowheads). Last somite boundary not detectable (n = 30, 2 of 3 experiments). j–l Treatments starting from 10 ss as indicated. j Normal segmentation in control. k 3 µM SB225002 no effect on myotome boundaries (inset) (n = 50, 5 of 7 experiments). l 2 µM XRP44X, myotome boundary defects along axis (brackets, insets), affecting segments formed prior to treatment (n = 40, 3 of 4 experiments). Scale bar for a–c, j–l = 200 µm, d–i = 50 µm