Expression of the BMP antagonist Dan during murine forebrain development.

Dan (Differential screening-selected gene aberrative in neuroblastoma, also known as N03) is a member of a class of glycoproteins shown to be secreted inhibitors of the transforming growth factor-beta (TGF-beta) and bone morphogenic protein pathways. We examined Dan expression during murine forebrain development from embryonic day 10.5 to postnatal day 14 and found that Dan was expressed in highly specific spatiotemporal patterns. In early telencephalic development, Dan is highly expressed in the fibroblasts covering the cortex. From E12.5-E14.5, Dan is also weakly expressed in a region of neuroepithelium at the medial margin of the telencephalon called the cortical hem. From E17.5 on, Dan is expressed strongly in CA3 pyramidal neurons of the hippocampus as well as in the developing thalamus and amygdala. To determine if Dan expression is correlated with the expression of any of its known ligand targets, we examined the expression of GDF-5, -6 and -7 in the forebrain and found that GDF-5 is expressed in Cajal-Retzius cells in Layer I of cortex, immediately adjacent to the expression of Dan in the meninges.