Frizzled9 protein is regionally expressed in the developing medial cortical wall and the cells derived from this region.

We used a newly generated antiserum specific for the Wnt receptor Frizzled9 to examine the distribution of this protein in the telencephalon. Previous studies showed expression of the mRNA for Frizzled9 in a medial high to lateral low gradient during cortical development 6. Our studies with the Frizzled9 antiserum supported this localization during mid-gestation mouse embryos. Later in gestation, the expression of Frizzled9 persisted in all cellular derivatives of the medial cortical neuroepithelium. From birth through adulthood, Frizzled9 continues to be expressed in the principal neuronal cells of the hippocampus. Interestingly, Frizzled9 was also expressed by astrocytic cells and dividing neuronal precursors in the adult dentate gyrus. Thus, Frizzled9 expression marks are a regional marker of medially derived cortical derivatives throughout rodent life and will be a useful marker in the study of regulation of cortical arealization.