Sema3D and Sema7A have distinct expression patterns in chick embryonic development

Abstract

By RT-PCR, we isolated a partial cDNA clone for the chick Semaphorin7A (Sema7A) gene. We further analyzed its expression patterns and compared them with those of the Sema3D gene, in chick embryonic development. Sema3D and Sema7A appeared to be expressed in distinct cell populations. In mesoderm-derived structures, Sema7A expression was detected in the newly formed somites, whereas Sema3D expression was found in the notochord. In ectoderm-derived tissues, Sema3D is expressed broadly in the surface ectoderm, lens and nasal placodes. Sema3D is also expressed in the developing nervous system including diencephalon, dorsal neural tube, optical and otic vesicles. In the limb bud, Sema3D expression was found throughout the ectoderm excluding the apical ectoderm ridge (AER), where Sema7A is concentrated. Although both genes appeared to be expressed in the migrating neural crest cells, Sema3D expression is limited to neural crest cells migrating out of the midbrain/hindbrain regions, while Sema7A expression is widespread in both cranial and trunk neural crest cells.

Fig. 1

Sequence analysis of the Sema7A-2 clone. A: Nucleotide sequence of Sema7A-2. The 44-nucleotides that are different from the annotated Sema7A gene are underlined. B: Comparison of amino acid sequence translated from the Sema7A-2 sequence with that of the annotated Sema7A gene. Note that the amino acid sequence is identical except the16–amino acid stretch. C: Comparison of the 16–amino acid sequences encoded by human, mouse, bovine, and chick Sema7A genes with that by Sema7A-2. Note that the 16–amino acid sequence of the chick Sema7A-2 is more homologous to the mammalian Sema7A proteins than the annotated chick Sema7A.

Fig. 2

Expression of Sema3D in early chick embryos (HH7 to HH12). Dorsal sides of embryos are shown for whole mount in situ hybridization results. For sections, the dorsal sides of the embryons are oriented upward. Whole mount in situ hybridization results are shown for embryos of (A) HH7, (B) HH10, (C) HH12 at a low magnification, and (D) HH12 at a higher magnification. After whole mount in situ hybridization, the embryos were sectioned. The planes of sections were shown with broken arrows and the numbers in parentheses next to the arrows indicate the figures showing the section results. E–H: Results from four section planes (1–4) of the HH12 embryo are shown after in situ hybridization with the Sema3D probe. n, notochord; nc, neural crest; nt, neural tube; mb, midbrain; hb, hindbrain; ov, otic vescicle; opv, optic vescicle; dnt, dorsal neural tube. Scale bars = 100 μm.

Fig. 3

Expression of Sema7A transcripts in early chick embryos at HH12. HH12 chick embryos were hybridized with the Sema7A-2 RNA probe, shown at the dorsal side of the embryo (A) and in the hindbrain region (B). The boxed area (1) in A is shown at a higher magnification in B. Note its expression in a restricted domain in hindbrain region and in some premigratory neural crest cells at the dorsal midline of the neural tube. The embryos were sectioned after whole mount in situ hybridization at the indicated section planes (2)–(4). nc, neural crest, hb, hindbrain, so, somite. Scale bars = 100 μm.

Fig. 4

Expression of Sema3D transcripts at HH stage 17. Lateral views (A, B) and a rear view (C) of the embryos are shown after whole mount in situ hybridization. The embryos were sectioned and the planes of sections are indicated by broken arrows. The numbers in parentheses next to the broken arrows indicate the figure numbers showing the section results. Note that the purple staining in the lens vesicles appears inside of the cells (D), suggesting that this is a signal of in situ hybridization, not trapping. aer, apical ectoderm ridge; np, nasal placode; fl, forelimb; hl, hindlimb; l, lens; nc, neural crest; oft, outflow tract; dnt, dorsal neural tube; sec, surface ectoderm. Scale bar in D = 250 μm, in E = 100 μm.

Fig. 5

Expression of Sema7A transcripts in HH17 chick embryos. Lateral views of the embryos (A, C) and a dorsal view of the midbrain/hindbrain regions (B) are shown. The section plane is indicated by a broken arrow and the section result is shown in D. Note the expression of Sema7A in migrating neural crest cells in cranial facial region (arrowheads in C) and in trunk region (D). so, somites; nc, neural crest; dm, dermomyotome; nt, neural tube. Scale bar = 100 μm.

Fig. 6

Expression of Sema3D transcripts in E3.5 chick embryos. A lateral view (A) and a frontal view in the forelimb bud area (B) are shown. Section planes are indicated by broken arrows and the results of the sections are shown in C–E. Note the staining in the otic vesicle in (A) is due to trapping. Dien, diencephalon; oft, outflow tract; aer, apical ectoderm ridge; sec, surface ectoderm. Scale bars = 100 μm.

Fig. 7

Expression of Sema7A transcripts in E3.5 chick embryos. A: In situ hybridizations were performed on whole mount E3.5 chick embryos. Section planes are shown with broken arrows and the results of section after in situ hybridization are shown in B–D (1–3). aer, apical ectodermal ridge; sec, surface ectoderm; dm, dermomyotome; nc, dorsal-laterally migrated neural crest cells; vnc, ventral-medially migrated neural crest cells. Scale bars = 100 μm.