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Results: 4

1.
Fig. 3.

Fig. 3. From: Direct and indirect roles for Nodal signaling in two axis conversions during asymmetric morphogenesis of the zebrafish heart.

Asymmetric cardiac jogging results in a L/R to D/V axis conversion. Shown are dorsal views of lefty2 expression in the heart at 20 hpf and 24–26 hpf (A, B, E, and F) and in transverse histological sections at 24–26 hpf with heart tubes outlined in black (C, D, G, and H). Sections in D and H have been stained with hematoxylin and eosin. In WT, lefty2 expression changes from left restricted expression at 20 hpf (A) to a symmetric extension at 24–26 hpf (B). Sections reveal that lefty2 localization is restricted to the dorsal side of the heart (C and D). swt morphants that likely express lefty2 on the right at 20 hpf (E) consistently display reversed cardiac jogging but also exhibit symmetric expression of lefty2 along the length of the heart tube (F). However, sections reveal a dorsal localization of lefty2 RNA, similar to WT (G and H). D, dorsal; V, ventral.

Kari Baker, et al. Proc Natl Acad Sci U S A. 2008 September 16;105(37):13924-13929.
2.
Fig. 2.

Fig. 2. From: Direct and indirect roles for Nodal signaling in two axis conversions during asymmetric morphogenesis of the zebrafish heart.

Asymmetric atrial cell migration promotes rotation of the cardiac cone. (A–H) Dorsal views of the heart in Tg(cmlc2:egfp) embryos between 18–21 hpf. (A–D) Dotted white lines indicate the embryonic midline. (E–H) Arrows indicate trajectories of left (red) and right (yellow) cells. A, E, C, and G are the first frames of time lapses (0 min), and B, F, D, and H are the final frames (180 min). A, B, E, and F are frames from a time lapse of a single WT embryo, and C, D, G, and H are frames from a time lapse of a single swt morphant. In WT embryos, the left atrial myocardium migrates asymmetrically along the left of the cone toward the left and anterior (E and F). The right cardiac cells also migrate toward the anterior and left, but rather than sweeping along the lateral edge of the cone, these cells migrate toward the lumen (E and F). In swt morphants the L/R directionality of these cellular trajectories is reversed (C, D, G, and H). L, left; R, right.

Kari Baker, et al. Proc Natl Acad Sci U S A. 2008 September 16;105(37):13924-13929.
3.
Fig. 1.

Fig. 1. From: Direct and indirect roles for Nodal signaling in two axis conversions during asymmetric morphogenesis of the zebrafish heart.

lefty2 expression temporally correlates with establishment of morphological asymmetries in the heart. Dorsal (A–C) and ventral (D–F) views of the heart from 20–30 hpf. Arrows indicate the ventricle and arrowheads the atrium (Di–Fiii). Cardiac cells were visualized by RNA in situ hybridization for cmlc2, expressed in all myocardial cells, and lefty2. In WT, lefty2 expression is restricted to the left myocardium at 20 hpf (Aii), but extends symmetrically along the length of the left-jogged heart by 22–28 hpf (Bii, Cii, and Dii). A swt morphant exhibits reversed lefty2 expression in the right myocardium (Aiii) at 20 hpf. At 22–28 hpf, lefty2 is expressed along the length of the right-jogged heart in swt morphants (Biii, Ciii, and Diii). At 28–30 hpf, lefty2 expression becomes restricted to the left side of the heart in WT (Eii) and is expressed exclusively along the left margin of the looping heart at 30 hpf (Fii). This process is reversed in swt morphants at 29 hpf. In this embryo, lefty2 expression is still visible across the atrium (Eiii, arrowhead) but it restricted to the right side of the ventricle (Eiii, arrow). Right-sided localization is more pronounced by 30 hpf, with lefty2 expression restricted to the right in both chambers (Fiii). The diagrams show atrial cells (light blue), ventricular cells (dark blue), localization of lefty2 (black hatchmarks). L, left; R, right; A, anterior; P, posterior.

Kari Baker, et al. Proc Natl Acad Sci U S A. 2008 September 16;105(37):13924-13929.
4.
Fig. 4.

Fig. 4. From: Direct and indirect roles for Nodal signaling in two axis conversions during asymmetric morphogenesis of the zebrafish heart.

A second rotation in the heart at 28–30 hpf converts the D/V axis back to the L/R axis. Cells are labeled with cmlc2::Dendra (green) and cmlc2::dsRED (red). A--H are dorsal views at 18–20 hpf; A2–H2 are ventral views at 48 hpf. White lines indicate the embryonic midline. WT embryos with left (A) or right (B) GFP at 20 hpf display a left-directed rotation of the heart at 28–30 hpf (A1 and B1). This rotation positions the original left cells from the dorsal side of the heart tube to the left of the looped heart (A2 and A3) where they contribute to the outer atrial (A2, arrowhead) chamber curvature. The original right cells are repositioned from the ventral side of the linear heart to the right of the looped heart at 48 hpf (B2 and B3) where they contribute to the outer curvature of the ventricle (B2, arrow) and the inner curvature of the atrium (B2, arrowhead). swt morphants with left jog and right loop display the same leftward rotation of the heart and contribution of original left cells to the inner ventricular (C2, arrow) and outer atrial (C2, arrowhead) chamber curvatures (C–C3). The asterisk in C marks GFP-expressing cells at 18 hpf that are to the right of midline. The asterisk in C2 marks the likely localization of these cells at 48 hpf on the right side of the looped heart. swt morphants with left GFP at 20 hpf (D) and exhibiting right jog and left loop display a right-directed rotation of the heart at 28–30 hpf (D1). This rotation positions the left, GFP-expressing cells to the left of the 48 hpf heart (D2 and D3) where they consistently contribute to the outer curvature of the ventricle (D2, arrow) and the inner curvature of the atrium (D2, arrowhead). spaw morphants with left jog and right loop display the same direction of heart-tube rotation and positioning of original left and right cardiac cells at 48 hpf as both WT and swt embryos with left jog and right loop (E–E3). The asterisk in E marks GFP-expressing cells at 18 hpf that are to the right of midline. The asterisk in E2 marks the likely localization of these cells at 48 hpf on the right side of the looped heart. spaw morphants with right jog and left loop show the same reversed direction of heart-tube rotation as swt morphants with this phenotype (F1). In this embryo, the original right cells (F) are repositioned to the right of the heart at 48 hpf (F2 and F3) and contribute to the inner curvature of the ventricle (F2, arrow) and the outer curvature of the atrium (F2, arrowhead). The same reversed direction of heart-tube rotation is observed in spaw morphants with right jog and right loop (G1). In this embryo, the original left cardiac cells (G) are positioned to the left of the heart at 48 hpf (G2 and G3). These cells are localized to the outer curvature of the ventricle (G2, arrow) and the inner curvature of the atrium (G2, arrowhead). spaw morphants lacking directional jog also lack a directed rotation of the heart tube at 28–30 hpf (H1). spaw morphants with original right expression of GFP at 20 hpf (H) display a maintenance of these cells on the right of the heart at 24–28 hpf and at 48 hpf (H2 and H3). In this embryo, the right GFP-expressing cells are localized to the inner curvature of the ventricle (H2, arrow) and the outer curvature of the atrium (H2, arrowhead). L, left; R, right; N, no; D, dorsal; V, ventral.

Kari Baker, et al. Proc Natl Acad Sci U S A. 2008 September 16;105(37):13924-13929.

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