INVOLVEMENT OF WNT-1 IN THE FORMATION OF THE MES METENCEPHALIC BOUNDARY

Wnt-1, a putative signaling molecule, is required before the 7 somite stage (E8.5) for the development of midbrain structures in the mouse. We show here that Wnt-1 is also needed for the formation of a boundary between the mesencephalic and metencephalic domains of the neural tub e. In embryos homozygous for the Wnt-1(sw) allele, mesencephalic and m etencephalic markers fail to segregate and the establishment of a stra ight limit of Otx-2 and Wnt-1 expression at the mid-hindbrain junction is impaired. In addition, as observed previously in heterotopic mes/m etencephalic transplantation experiments in avian embryos, Wnt-1 expre ssion is induced at the border of ectopic mes- and metencephalic islan ds observed in Wnt-1(sw/sw) mutants, suggesting that, in situ, interac tions between mes- and metencephalic cells reinforce Wnt-1 expression at the boundary.