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

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 pr esent a thorough description of the Xvax2 expression pattern all along Xeno pus embryogenesis, and compare this pattern in detail to that shown by Xvax 1b and Xpax2, two genes also involved in ventral eye development. At early neurula stages, while Xpax2 starts to be expressed within the eye field, bo th Xvax2 and Xvax1b are exclusively activated in the presumptive ventral te lencephalon. Since midneurula stages, Xvax2 and Xvax1b are also transcribed in the medial aspect of the eye field. At tailbud and tadpole stages, Xvax 2, Xvax1b and Xpax2 expression overlaps in the optic stalk and nerve and in the optic disk, while Xvax2 and Xvax1b also display specific activation do mains in the ventral retina as well as in the ventral telencephalon and die ncephalon. Finally, during metamorphosis a high level of both Xvax2 and Xva x1b transcription is maintained in the optic chiasm. In addition, Xvax1b is transcribed in the ventral hypothalamus and in the hypophysis, whereas a s trong Xvax2 expression is retained in the ventral portion of the mature ret ina. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.