Fate map of the avian anterior forebrain at the four-somite stage, based on the analysis of quail-chick chimeras

To better understand the topological organization of the primordia within t he anterior forebrain, we made a fate map of the rostral neural plate in th e chick. Homotopic grafts at the four-somite stage were allowed to survive for up to 9 days to enable an analysis of definitive brain structures. In s ome cases, the topography of the grafted neuroepithelia was compared with g ene expression patterns. The midpoint of the anterior neural ridge maps upo n the anterior commissure in the closed neural tube, continuing concentrica lly into the preoptic area and optic field. Non-neural epithelium just in f ront of this median ridge gives rise to the adenohypophysis. Areas for the presumptive pallial commissure, septum, and prosencephalic choroidal tissue lie progressively more posteriorly along the ridge, peripheral to the tele ncephalic entopeduncular and striatopallidal primordia (the subpallium), an d the pallium (olfactory bulb, dorsal ventricular ridge, and cortical domai ns). Subpallial structures lie topologically anterior to the pallial format ions, and both are concentric to the septum. Within the pallium, the major cortical domains (Wulst and caudolateral, parahippocampal, and hippocampal cortices) appear posterior to the dorsal ventricular ridge. The amygdaloid region appears concentrically across both the subpallial and pallial region s. This fate map shows that the arrangement of the prospective primordia in the neural plate is basically a flattened representation of topological re lationships present in the mature brain, though marked phenomena of differe ntial growth and selective tangential migration of some cell populations co mplicate the histogenetic constitution of the mature telencephalon. (C) 200 1 Academic Press.