Members of the Wnt, Fz, and Frp gene families expressed in postnatal mouse cerebral cortex.

The functions of Wingless-Int (Wnt) signaling, studied intensely in embryonic brain development, have been comparatively little investigated in the postnatal brain. We report remarkably patterned gene expression of Wnt signaling components in postnatal mouse cerebral cortex, lasting into young adulthood. Wnt genes are expressed in gene-specific regional and lamina patterns in each of the major subdivisions of the cerebral cortex: the olfactory bulb (OB), the hippocampal formation, and the neocortex. Genes encoding Frizzled (Fz) Wnt receptors, or secreted Frizzled-related proteins (sFrps), are also expressed in regional and lamina patterns. These findings suggest that Wnt signaling is active and regulated in the postnatal cortex and that different cortical cell populations have varying requirements for a Wnt signal. The OB, in particular, shows gene expression of a large variety of Wnt signaling components, making it a prime target for future functional studies. The penultimate components of the canonical Wnt pathway are the Tcf/Lef1 transcription factors, which regulate transcription of Wnt signaling target genes. Surprisingly, we found little Tcf/Lef1 expression in the postnatal neocortex. These observations suggest that noncanonical Wnt pathways predominate, which will require functional testing. However, Lef1 is widely expressed in the dorsal thalamus, and Wnt ligands and receptors are expressed, respectively, in cortical areas and thalamic nuclei that are interconnected. Thus, canonical Wnt signaling could be utilized in a major cortical input by Fz- and Lef1-expressing thalamic cells that innervate the Wnt-expressing cortex.