The Cortical Hem in the Chick Telencephalon: Evidence of a Signaling Center Implicated in Patterning the Dorsal Forebrain
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Embryonic signaling centers regulate cell fate specification and patterning of the developing organism. The notochord, floor plate, and roofplate are putative signaling centers responsible for patterning the dorsoventral axis of the developing central nervous system. They are characterized by their inductive capacity and the expression of distinct signal peptides including Wnts, sonic hedgehog, and bone morphogenetic proteins (Bmp) , all of which mediate cell-cell communication and facilitate embryonic induction. The cortical hem is a recently discovered signaling center in mouse which expresses multiple Wnt genes and Bmps. Located at the junction of the choroid plexus epithelium and the presumptive hippocampus, the cortical hem is positioned to provide signaling information to pattern the dorsal telencephalon. We sought to characterize the hem in the chick telencephalon. A chick model of the hem would greatly facilitate further experimentation using explant cultures and retroviral infection. Using in situ hybridization techniques, we have obtained data indicating the presence of the cortical hem in chick. Though the precise molecules that may define the chick cortical hem continue to elude us, PCR data suggest that Wnt genes are present in the medial wall of the telencephalon. To examine the role of Bmps in the hem, we attempted to block Bmp activity by expressing a dominant negative Bmp receptor using an avian retroviral vector. Though initial results were inconclusive, control experiments have shed light on viral transfection efficiency, the scope of viral infection after injection, and the overall feasibility of this potentially powerful approach.With honors.