Expression of sema3G in the somites. (A) Diagram of zebrafish embryo at 19 hpf, showing locations of the cross-sections through the anterior (B), posterior (C), and tail (D) somites. (B) In the anterior trunk somites sema3G is expressed in the cells at the lateral somite surface. (C) In the posterior trunk somites sema3G is expressed in cells adjacent to the neural tube and notochord. (D) In the tail, sema3G is expressed in a column of somite cells adjacent to the notochord (arrowheads). (E) Lateral view at 24 hpf showing that sema3G first diminishes in the central trunk region. (F and G) Higher magnification images of embryo in (E), showing sema3G expression remains in the anterior somites (arrowheads in F) and in the new somites of the tail (arrowheads in G). Arrow in (F) indicates out-of-focus labeling of the pronephros along the yolk. (H) Confocal projection (dorsal view) of embryo at 18 hpf, double-stained for sema3G mRNA (red) and F59 antibody (green), which stains myosin heavy chain isoforms in fish. (I) Lateral views of the trunk of yot (top) and wild type embryos (bottom) at 18 hpf. yot embryos do not express sema3G in the trunk. Asterisk: notochord. Scale bar in panels B–D and F–H=50 μm. Scale bars in E and I=100 μm.

Expression of sema3G in the brain. (A and B) Ventral views of midbrain region in 24 hpf (A) and 28 hpf (B) embryos showing sema3G expression in bilateral clusters in the ventral midbrain (arrowheads). At 28 hpf, bilateral expression is also seen in the diencephalon (arrows in B). (C) Diagram showing relative positions of thick cross-sections of the midbrain regions (red, D–G) and telencephalon (green, H–K). (D) Cross section through midbrain at 36 hpf shows sema3G is expressed in the ventral midbrain (arrowheads) and diencephalon (arrows). (E–H) Sections at 48 hpf (E–F) and 60 hpf (G–H). (E) sema3G is expressed in the diencephalon (arrows), with diffuse expression in the ventral midbrain. (F) Staining with a sense probe to sema3G does not show this expression. (G) sema3G still is expressed in the diencephalon at 60 hpf (arrows). (H) At 60 hpf sema3G is expressed in the region of the optic nerve head (arrowhead). (I–K) Anterior views at 48 hpf (I), 60 hpf (J) and 84 hpf (K) shows expression in the telencephalon has formed a distinct bilateral pattern, with strongly expressing cells (arrowheads) dorsomedial to the olfactory epithelium (oe). The arrow in (K) indicates a melanocyte. (L) Sagittal section at 84 hpf shows that sema3G is expressed in close proximity to the olfactory epithelium. Anterior is to the left and dorsal is up. The eye was removed to facilitate viewing. Scale bars=50 μm.

Expression of sema3G in the pharyngeal arches, pectoral fin buds, and pronephric ducts. (A) Ventral view at 48 hpf of the developing pharyngeal arches showing that sema3G is expressed in the ventral part of each arch (arrowheads). (B and C) Sagittal sections at 48 hpf (B) and 60 hpf (C) showing the expression of sema3G in the arch mesenchyme. (D and E) Lateral views of the pectoral fin bud at 48 hpf (D) and 60 hpf (E) showing that sema3G is expressed in the mesenchyme of the developing pectoral fin bud, but is not detected in the apical ectodermal ridge (arrowhead in E). (F) Lateral view of trunk at 22 hpf showing sema3G expression in the developing pronephric ducts (arrowheads). Scale bars for A to E=50 μm. Scale bar in F=25 μm.

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