Dorsoventral patterning of the telencephalon is disrupted in the mouse mutant extra-toes(J)

Little is known about the mechanisms that control the development of region al identity in the mammalian telencephalon. The Gli family of transcription factor genes is involved in the regulation of pattern at many sites in the embryo and is expressed in the embryonic mouse telencephalon. We have anal yzed telencephalic patterning in the extra-toes (J) (Xt(J)) mouse mutant, w hich carries a deletion in the Gli family member Gli3. We report that dorso ventral patterning of the telencephalon is dramatically disrupted in the Xt (J) mutant. Specific dorsal telencephalic cell types and gene expression pa tterns are lost in homozygous Xt(J) mutants, and features of ventral telenc ephalic identity develop ectopically in the dorsal telencephalon. This part ial ventralization of the dorsal telencephalon does not appear to be induce d by an expansion of Sonic hedgehog expression in the telencephalon, but ma y be due to a loss of Bmp and Wnt gene expression in a putative dorsal tele ncephalic signaling center, the cortical hem. Our findings suggest that in dorsal telencephalon Gli3 is needed to repress ventral telencephalic identi ty. (C) 2000 Academic Press.