Nitta KR et al. (2006), Expression of Sox1 during Xenopus early embryog...

XB-ART-34733

Biochem Biophys Res Commun 2006 Dec 08;3511:287-93. doi: 10.1016/j.bbrc.2006.10.040.

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Expression of Sox1 during Xenopus early embryogenesis.

Nitta KR , Takahashi S , Haramoto Y , Fukuda M , Onuma Y , Asashima M .

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Sox B1 group genes, Sox1, Sox2, and Sox3 (Sox1-3), are involved in neurogenesis in various species. Here, we identified the Xenopus homolog of Sox1, and investigated its expression patterns and neural inducing activity. Sox1 was initially expressed in the anterior neural plate of Xenopus embryos, with expression restricted to the brain and optic vesicle by the tailbud stage. Expression subsequently decreased in the eye region by the tadpole stage. Sox1 expression in animal cap explants was induced by inhibition of BMP signaling in the same manner as Sox2, Sox3, and SoxD. In addition, overexpression of Sox1 induced neural markers in ventral ectoderm and in animal caps. These results implicate Xenopus Sox1 in neurogenesis, especially brain and eye development.

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Species referenced: Xenopus laevis
Genes referenced: chrd ncam1 nos1 sox1 sox15 sox17a sox2 sox3

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	Fig. 1. (A) Alignment of Sox1 amino acid sequences in various species. Identical amino acids are shaded in gray, and conserved amino acid substitutions are shaded in light gray. The conserved Sox1-type HMG-box domain is boxed. Xenopus Sox1 shares 71% sequence identity with newt Sox1, 69% with chick, 68% with mouse, and 69% with human. (B) Rooted phylogeny of Sox1–3, SoxD, and Sox17a amino acid sequences. X. laevis Sox17a was used as the outlier. Xl, X. laevis; Cp, Cynops pyrrhogaster; Gg, Gallus gallus; Mm, Mus musculus; Hs, Homo sapiens. Sequence sources (GenBank Accession Nos.) are as follows: X. laevis Sox2 (AAB62821) [24], Sox3 (CAA68828) [12], SoxD (AB013896) [14], Sox17a (CAA04957) [25]; Cynops pyrrhogaster Sox1 (AB154820) [26]; G. gallus Sox1 (BAA25092) [27], Sox2 (P48430) [27,28], Sox3 (P48433) [28]; Mus musculus Sox1 (AB108672) [29], Sox2 (P48432) [30], Sox3 (P53784) [8,29,31]; Homo sapiens Sox1 (O00570) [32], Sox2 (CAA83435) [33], Sox3 (P41225) [34].
	Fig. 2. Temporal expressions of Sox1–3 and SoxD during Xenopus development. RT-PCR analysis was performed at various developmental stages. Sox1 and Sox2 transcripts appeared at stage 11 and were detected until stage 38. Sox3 and SoxD transcripts were detected in unfertilized eggs and in embryos up to stage 38. Numbers indicate developmental stages. U, unfertilized egg.
	Fig. 3. Spatial expression patterns of Sox1–3 and SoxD revealed by whole-mount in situ hybridization. In dorsal views of stage 13 and 17, the anterior is at the bottom of the panel. Arrowheads and arrows indicate the dorsal lip and the yolk plug, respectively. Sox1 expression was not detected at stage 11. At stage 35, Sox1 expression was detected throughout the brain and the tail.
	Fig. 4. Expression patterns of Sox1-3 and SoxD in sectioned embryos. Fixed embryos were dissected at the line indicated in (A) (stage 28) and in (B) (stage 35). Sox1–3 and SoxD were expressed in the diencephalon at stage 28 (C–F). Sox1, Sox2, and SoxD were also expressed in the optic vesicle (C,D,F). Sox3 was expressed strongly in the epidermis of the optic vesicle (E, arrowhead). At stage 35, Sox1 was expressed in the diencephalon and was weakly expressed in the eye (G). Sox2 and SoxD were expressed in the diencephalon, the neural retina, and the lens (H,J). Sox3 was expressed in the diencephalon and the lens, but not in the neural retina (I, arrowhead). A bar in (C) indicates 200 lm. dc, diencephalon; ep, epidermis; nr, neural retina; ov, optic vesicle; ln, lens.
	Fig. 5. Sox1–3 and SoxD are induced by inhibition of BMP signaling in animal caps. Animal caps were dissected at stage 9 from embryos uninjected () or injected with 50 pg of chordin mRNA (+), and were cultured until the sibling embryos reached stages 11, 13, 18, and 25. W.E., whole embryos.
	Fig. 6. Sox1 induces neural tissue and neural gene expression. (A,B) Embryos were coinjected with 100 pg of Sox1 mRNA and b-gal mRNA into both A4 blastomeres of 32-cell stage embryos. Overexpression of Sox1 induced neural tissue recognized by NEU-1. (A0,B0) High magnification views of (A) and (B). Arrowheads indicate overexpressed regions. (C) Overexpression of Sox1 mRNA induces neural genes, NCAM, and Ntublin (N-tub), without inducing a mesodermal gene, MS-actin in animal caps. Animal caps were dissected from embryos injected with 100 pg of Sox1 mRNA, and cultured until sibling embryos reached stage 32. W.E., whole embryos.