Figure 8.

Differential rescue of marker genes in Zic1 morphants by overexpression of cyp26a1 and shh mRNA. (A–Z) Forebrain region, dorsal view, rostral to the bottom. (A–T) 22-somite stage; (U–Z) Two-somite stage. (A–E) Abolished vax1 expression in Zic1 morphants can be rescued by overexpression of shh mRNA. Cyp26a1 mRNA overexpression in Zic1 morphants does not rescue vax1 expression. Simultaneous overexpression of shh and cyp26a1 leads to a similar rescue as with shh only. (F–J) Reduced vax2 expression in Zic1 morphants can be rescued to some extent by shh overexpression. Cyp26a1 overexpression in Zic1 morphants causes a further reduction of vax2 expression, however. Simultaneous overexpression of shh and cyp26a1 in Zic1 morphants results in a similar reduction of vax2 expression as with cyp26a1 only. Brackets indicate proximal-distal expansion. (K–O) Overexpression of cyp26a1 rescues dorsal expansion of pax2 in Zic1 morphants. Dorsal expansion of pax2 expression in the prospective retina of Zic1 morphants is promoted by shh overexpression. Simultaneous overexpression of shh and cyp26a1 leads to similar expansion as with shh only. Brackets indicate ventral–dorsal expansion. (P–T) Overexpression of cyp26a1 in Zic1 morphants leads to a rescue of dorsal pax6 retraction. Dorsally retracted pax6 expression in Zic1 morphants is exacerbated by shh overexpression. Pax6 expression after simultaneous overexpression of shh and cyp26a1 in Zic1 morphants resembles pax6 expression in Zic1 morphants. (U–Z) Reduced cyc and shh expression in Zic1 morphants (arrowhead) cannot be rescued by cyp26a1 overexpression. (som) Somite stage; (n/a) not applicable.