Abnormal Positioning of Diencephalic Cell Types in Neocortical Tissue in the Dorsal Telencephalon of Mice Lacking Functional Gli3

Abstract

The transcription factor Gli3 (glioma-associated oncogene homolog) is essential for normal development of the mammalian forebrain. One extreme requirement for Gli3 is at the dorsomedial telencephalon, which does not form in Gli3Xt/Xt mutant mice lacking functional Gli3. In this study, we analyzed expression of Gli3 in the wild-type telencephalon and observed a high dorsal-tolow ventral gradient of Gli3 expression and predominance of the cleaved form of the Gli3 protein dorsally. This graded expression correlates with the severe dorsal-tomild ventral telencephalic phenotype observed in Gli3Xt/Xt mice. We characterized the abnormal joining of the telencephalon to the diencephalon and defined the medial limit of the dorsal telencephalon in Gli3Xt/Xt mice early in corticogenesis. Based on this analysis, we concluded that some of the abnormal expression of ventral telencephalic markers previously described as being in the dorsal telencephalon is, in fact, expression in adjacent diencephalic tissue, which expresses many of the same genes that mark the ventral telencephalon. We observed occasional cells with diencephalic character in the Foxg1 (forkhead box)-expressing Gli3Xt/Xt telencephalon at embryonic day 10.5, a day after the anatomical subdivision of the forebrain vesicle. Large clusters of such cells appear in the Gli3 Xt/Xt neocortical region at later ages, when the neocortex becomes highly disorganized, forming rosettes comprising mainly neural progenitors. We propose that Gli3 is indispensable for formation of an intact telencephalic-diencephalic boundary and for preventing the abnormal positioning of diencephalic cells in the dorsal telencephalon.

TheGli3Hypomorphic MutationPdnCauses Selective Impairment in the Growth, Patterning, and Axon Guidance Capability of the Lateral Ganglionic Eminence

“…Confirming previous findings, Gli3 transcripts are restricted mainly to the ventricular zones of the developing cortex, VT, and thalamus of wild-type embryos (Fig. 1A-D) (Hui et al, 1994;Fotaki et al, 2006). In the VT, Gli3 shows a lateral high to medial low gradient of expression with low expression levels in the MGE.…”

“…8, available at www.jneurosci.org as supplemental material). Collectively, these phenotypes suggest that normal LGE development is highly sensitive to changes in Gli3 expression levels consistent with its position between the dorsal telencephalon, in which the Gli3 repressor predominates, and the MGE with high levels of Gli3 activator (Fotaki et al, 2006). The relative severity of the LGE phenotypes in Pdn/Pdn mutants is also in contrast to mice lacking Gli3 completely.…”

“…Protein was extracted from VT of E12.5 wild-type and Pdn/Pdn embryos as described previously (Fotaki et al, 2006). Equivalent amounts of protein were subjected to gel electrophoresis on a 3-8% gradient Tris-acetate gel (Invitrogen), and protein was transferred to a nitrocellulose membrane, which was incubated with rabbit polyclonal anti-Gli3 antibody (1:500; Abcam).…”

“…Similarly, Gli transcription factors, critical components of the Shh signaling pathway, are required for telencephalic development. Mutations in Gli3, in particular, affect the development of both ventral and dorsal components of the telencephalon (Grove et al, 1998;Theil et al, 1999;Tole et al, 2000;Kuschel et al, 2003;Theil, 2005;Fotaki et al, 2006;Friedrichs et al, 2008;Quinn et al, 2009;Yu et al, 2009a). In the dorsal telencephalon, Gli3 controls patterning independently of Shh, but in the VT, Gli3 transcription and cleavage of Gli3 protein into its repressor form are suppressed by Shh signaling, resulting in a dorsal high to ventral low gradient of Gli3 expression.…”

A Crucial Role for Primary Cilia in Cortical Morphogenesis

“…Several phenotypes seen in cbs/cbs mutants resemble that seen in the Gli3 deletion mutant Xt J , including polydactyly, defects in the determination of dorsal telencephalic tissue, the formation of rosette-shaped heterotopias in the dorsal cortex, and the relaxation of the telencephalic-diencephalic boundary (Johnson, 1967;Theil et al, 1999;Tole et al, 2000;Fotaki et al, 2006). This prompted us to examine Gli3 expression patterns in the cbs mutant.…”