Role of Pax3/7 in the tectum regionalization

Pax3/7 is expressed in the alar plate of the mesencephalon. The optic tectu m. differentiates from the alar plate of the mesencephalon, and expression of Pax3/7 is well correlated to the tectum development. To explore the func tion of Pax3 and Pax7 in the tectum development, we misexpressed Pax3 and P ax7 in the diencephalon and ventral mesencephalon. Morphological and molecu lar marker gene analysis indicated that Pax3 and Pax7 misexpression caused fate change of the alar plate of the presumptive diencephalon to that of th e mesencephalon, that is, a tectum and a torus semicircularis were formed e ctopically. Ectopic tectum in the diencephalon appeared to be generated thr ough sequential induction of Fgf8, En2 and Pax3/7. In ventral mesencephalon , which expresses En but does not differentiate to the tectum in normal dev elopment, Pax3 and Pax7 misexpression induced ectopic tectum. In normal dev elopment, Pax3 and Pax7 expression in the mesencephalon commences after Otx 2, En and Pax2/5 expression. In addition, expression domain of Pax3 and Pax 7 is well consistent with presumptive tectum region in a dorsoventral axis. Taken together with normal expression pattern of Pax3 and Pax7, results of misexpression experiments suggest that Pax3 and Pax7 define the tectum. re gion subsequent to the function of Otx2 and En.