EXT1 is a protein directly involved with the synthesis of  Heparan sulfate, 
a proteoglycan itself implicated in FGF  signaling.  We use Emx1-cre mice to conditionally 
knock ext1 out specifically in the developing telencephalon, thus allowing us to assess 
the role of heparan sulfate in cortical development.  Phenotypic analysis is based 
on in  situ hybridization of markers indicative of either cortical arealization 
or the expression of FGF target genes.