Fig. 3. Constructing a Wnt3a-IRES-xneox-dt-a mouse line to ablate the hem. (A, top to bottom) Wild-type Wnt3a allele; Wnt3a-IRES-xneox-dt-a allele; activation of dt-a toxin by Cre-recombination, using an Emx1-IRES-Cre mouse line (Gorski et al., 2002). (B) Recombination in the telencephalon was confined to the hem, which was almost completely ablated by E10 in Wnt3a^{IRESxneoxdt-a/+};Emx1^IRESCre/+ mice (dorsal views). Wnt3a expression marks the hem at E12.5 (medial view) but not in a hem-ablated brain (arrow indicates caudal hem remnant). Expression of Lmx1a marks the hem and cpx; a part of the cpx (arrow) remains in the hem-ablated mouse.