Fig. 2

Knockdown of sulf1 leads to somite defects including loss of the horizontal myoseptum. (A) Whole mount view of three fish injected with control morpholino and fixed at 24 hpf, showing normal tail development. (B) Whole mount view of three fish injected with 0.25 pmol sulf1 MO, showing curvature and widening of the tail. (C) Higher magnification view of a control fish at 24 hpf, showing normal chevron-shaped somites. (D) Higher magnification view of a sulf1 morphant fish showing more closely spaced, obtusely angled somites. (E) Lateral view of whole-mount of 48 hpf control zebrafish labeled with 488-conjugated phalloidin. Again normal chevron-shaped somites can be seen. (F) Cross-section of control zebrafish labeled with 488-conjugated phalloidin with arrows marking the distinct horizontal myoseptum that runs along the midline of the fish, counterstained with DAPI. (G) Lateral view of whole-mount of 48 hpf sulf1 morphant zebrafish labeled with 488-conjugated phalloidin, taken at the same exposure and settings as (E). Labeled muscle fibers are much less dense than in controls, and the somites appear rounded, more obtusely angled, and closer together. (H) Cross-section of sulf1 morphant fish at 48 hpf, showing the sparser muscle fibers and the absence of a morphological horizontal myoseptum. (I and J) Quantification of somite width (I) and angle (J) between control and sulf1 morphant fish. Quantification was done on the two somites closest to the proctodeum (approximately somite 15). sulf1 morphants had significantly narrower somites that had a significantly more obtuse angle than control fish (p<0.001 for both, T-test). (K and L) Vibratome cross-section of control (K) or sulf1 morphant (L) zebrafish at 48 hpf stained with hemotoxylin and eosin showing the decreased density of muscle fibers and loss of the horizontal myoseptum in sulf1 morphants. Scale bars: A, B: 500 μm; C, D: 250 μm; E, G: 50 μm; F, H: 50 μm; K, L: 50 μm.