Pax6-dependent regulation of adhesive patterning, R-cadherin expression and boundary formation in developing forebrain.

Mutations in the gene for the transcription factor, Pax6, induce marked developmental abnormalities in the CNS and the eye, but the cellular mechanisms that underlie the phenotype are unknown. We have examined the adhesive properties of cells from the developing forebrain in Small eye, the Pax6 mutant mouse. We have found that the segregation normally observed in aggregates of cortical and striatal cells in an in vitro assay is lost in Small eye. This correlates with an alteration of in vivo expression of the homophilic adhesion molecule, R-cadherin. Moreover, the boundary between cortical and striatal regions of the telencephalon is dramatically altered in Small eye: radial glial fascicles do not form at the border, and the normal expression of R-cadherin and tenascin-C at the border is lost. These data suggest a link between the transcription factor, Pax6, R-cadherin expression, cellular adhesion and boundary formation between developing forebrain regions.