Characterization of cis-regulatory elements of the homeobox gene Xanf-1.

Investigation of molecular mechanisms underlying early patterning of the nervous system is an important task of modern developmental biology. Previously, we identified a novel homeobox gene, Anf, that is expressed in the most anterior zone at the beginning of neuroectoderm specification. The expression pattern of Anf corresponds to primordia of the telencephalon and the rostral part of the diencephalon. In the present work, we investigated cis-regulation of expression of the Xenopus laevis Anf, Xanf-1. Two elements, highly conserved in Xenopus, chick and human, were identified within the Xanf-1 promoter region. The first element, located near position -500, is necessary for overall enhancement of the Xanf-1 expression. The second element, near position -200, is crucial for maintenance of the Xanf-1 expression at moderate levels and also for specific localization of the expression in the anterior neuroectoderm. Thus, the distal part of this element is responsible for suppression of Xanf-1 posterior to the normal expression domain of this gene. The data obtained corroborate with the Nieuwkoop two-signal model of neural induction. This model states that at the first step of induction, all neuroectoderm acquires potencies to develop toward forebrain structures, but later these potencies are suppressed in posterior regions.