Fig. 3. Effect of reduction of her7 function on segmentation. The myotome boundaries of the trunk marked by twitchin expression are shown in 26 hpf embryos in lateral view, anterior towards the left and dorsal upwards (A-D). The expression of segmental genes in the presomitic mesoderm and trunk somites of embryos at 14 hpf (10 somites) are shown in dorsal view after flat mounting with anterior upwards (F-U). Arrows and arrowheads indicate localized defects and brackets indicate the extent of larger regions of abnormalities. The effect of increasing her7m2 dose on myotome boundaries at 26 hpf is shown in A-D. (A) Uninjected control. Embryos injected with 1 ng/µl (B), 3 ng/µl (C) and 5 ng/µl (D) her7m2. (E) Histogram showing the restricted distribution of the most anterior segmental defect, assayed at 26 hpf. The effect of increasing her7m1 dose on the expression of myod is shown in F-I. (F) Uninjected control, (G) injected with 3 ng/µl, (H) 4 ng/µl and (I) 5 ng/µl her7m1. The disruption of segment organization and polarity by her7m2 injection is shown in J-U. The expression of dld (J,K), notch5 (L,M), paraxial protocadherin (N,O), mespa (P,Q), mespb (R,S) and notch1a (T,U) is shown for uninjected controls (J,L,N,P,R,T) and after injection with 7 ng/µl her7m2 (K,M,O,Q,S,U, indicated with +). Scale bar: in A, 250 µm for A-D.