A vertebrate gene related to orthodenticle contains a homeodomain of the bicoid class and demarcates anterior neuroectoderm in the gastrulating embryo.

We studied the expressionoftwovertebratehomeobox genes, Otxl and Otx2, related to orthodenticle, a gene expressed in the developing head of Drosophila. Both genes are expressed in restricted regions of thedeveloping rostral brain including the presumptive cerebral cortex and olfactory bulbs. The expression patterns of the two genes in diencephalon suggest that they both have a role in establishing the boundary between presumptive dorsal and ventral thalamus.They are also expressed in regions of the developing olfactory,auricolar and ocular system, including the covering of the optic nerve.Otxl expression is detectable from day 8 of gestation in telencephalic, diencephalic and mesencephalic regions. From day 10.5 ofgestationitsexpressionextendstosomemetencephalic areas. Otx2 appears to be already expressed in the epiblast of prestreak embryos. It persists in the entire embryonic ectoderm for some time after the onset of gastrulation.In midstreak embryos its expression appears progressively restricted to the anterior embryonic ectoderm corresponding to presumptive fore- and mid- brain.In early midgestation embryos it is expressed in telencephalic,diencephalic and mesencephalic regions but from day 11.75 of gestation its expression disappears from dorsal telencephalon and is confimed to diencephalic and mesencephalic regions. Otx2 is one of the earliest genes expressed in the epiblast and immediately afterwards is expressed in anterior neuroectoderm, demarcating rostral brain regions even before headfold formation.Its gene product contains a homeodomain of the bicoid class and is able to recognize and transactivate a bicoid target sequence.