Liu Y et al. (2001), Expression of the Xvax2 gene demarcates presump...

XB-ART-9832

Mech Dev 2001 Jan 01;1001:115-8. doi: 10.1016/s0925-4773(00)00505-0.

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Expression of the Xvax2 gene demarcates presumptive ventral telencephalon and specific visual structures in Xenopus laevis.

Liu Y , Lupo G , Marchitiello A , Gestri G , He RQ , Banfi S , Barsacchi G .

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vax2 is a recently isolated homeobox gene, that plays an important role in controlling the dorso-ventral patterning of the retina. In this paper we present a thorough description of the Xvax2 expression pattern all along Xenopus embryogenesis, and compare this pattern in detail to that shown by Xvax1b and Xpax2, two genes also involved in ventral eye development. At early neurula stages, while Xpax2 starts to be expressed within the eye field, both Xvax2 and Xvax1b are exclusively activated in the presumptive ventral telencephalon. Since midneurula stages, Xvax2 and Xvax1b are also transcribed in the medial aspect of the eye field. At tailbud and tadpole stages, Xvax2, Xvax1b and Xpax2 expression overlaps in the optic stalk and nerve and in the optic disk, while Xvax2 and Xvax1b also display specific activation domains in the ventral retina as well as in the ventral telencephalon and diencephalon. Finally, during metamorphosis a high level of both Xvax2 and Xvax1b transcription is maintained in the optic chiasm. In addition, Xvax1b is transcribed in the ventral hypothalamus and in the hypophysis, whereas a strong Xvax2 expression is retained in the ventral portion of the mature retina.

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Species referenced: Xenopus laevis
Genes referenced: foxg1 pax2 rax vax1 vax2

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	Fig. 1. Whole-mount single or double in situ hybridizations on stage 13/14 (A,D,F,G,J,L,M,P,R), stage 15/16 (B,E,H,K,N,Q) and stage 19 (C,I,O) Xenopus embryos, showing expression of Xvax2 (Aâ€“F,R, blue staining) in comparison with Xvax1b (Gâ€“L, blue staining) and Xpax2 (Mâ€“Q, blue staining; R, magenta staining). Xrx1 (D,E,J,K,P,Q, magenta staining) and XBF1 (F,L, magenta staining) are used as markers of eye field and telencephalon, respectively.
	Fig. 2. Expression of Xvax2 (A,D), Xvax1b (B,E) and Xpax2 (C,F) as detected in transverse sections of stage 23 Xenopus embryos following whole-mount in situ hybridization, cut at the level of the anterior (Aâ€“C) or posterior (Dâ€“F) optic vesicle. m, mesencephalon; ov, otic vesicle.
	Fig. 3. Expression of Xvax2 (Aâ€“D), Xvax1b (Eâ€“H), Xpax2 (Iâ€“K) as detected in transversal sections of stage 30 Xenopus embryos following whole-mount in situ hybridization. Left to right sections show expression at progressively posterior levels. h, hypothalamus; m, mesencephalon; os, optic stalk; vt, ventral telencephalon.
	Fig. 4. Expression of Xvax2 (Aâ€“D), Xvax1b (Eâ€“H), Xpax2 (Iâ€“K) as detected in transversal sections of stage 33 Xenopus embryos following whole-mount in situ hybridization. Left to right sections show expression at progressively posterior levels. h, hypothalamus; os, optic stalk; vt, ventral telencephalon.
	Fig. 5. Expression of Xvax2 (Aâ€“C,G,H) and Xvax1b (Dâ€“F,I) as detected in transversal sections of stage 41/42 Xenopus embryos following whole-mount in situ hybridization. (Aâ€“F) Left to right sections show expression at progressively posterior levels; arrowhead points to the hypophysis. (Gâ€“I) Transversal sections under a higher magnification show the expression of Xvax2 in the ventral part of the retina (G,H) and the coexpression of Xvax2 (H) and Xvax1b (I) in the optic nerve (arrows). h, hypothalamus; ch, optic chiasm.
	Fig. 6. Expression of Xvax2 (Aâ€“C,G,H) and Xvax1b (Dâ€“F) as detected in dissected brains (Aâ€“F) and neural retinas (G,H) of stage 48 (A,B,D,E,G) and stage 59/60 (C,F,H) embryos by whole-mount in situ hybridization. (A,D) Lateral views; (B,C,E,F) Ventral views. Anterior is to the left for (Aâ€“F) and dorsal is up for (A,D,G,H). (Aâ€“F) From anterior to posterior, the staining locates at ventral telencephalon (vt), optic chiasm (ch), hypothalamus (h) and pituitary gland (p), respectively, as labeled in (C,F).
	vax2 (ventral anterior homeobox 2) gene expression in Xenopus laevis embryo via in situ hybridization, transverse section through head region, anterior to optic vesicle, NF stage 23. anterior top.
	vax1 (ventral anterior homeobox 1) gene expression in Xenopus laevis embryo via in situ hybridization, transverse section through head region, anterior to optic vesicle, NF stage 23, anterior top.