In utero fate mapping reveals distinct migratory pathways and fates of neurons born in the mammalian basal forebrain

Recent studies suggest that neurons born in the developing basal forebrain migrate long distances perpendicularly to radial glia and that many of thes e cells reach the developing neocortex. This form of tangential migration, however, has not been demonstrated in vivo, and the sites of origin, pathwa ys of migration and final destinations of these neurons in the postnatal br ain are not fully understood. Using ultrasound-guided transplantation in ut ero, we have mapped the migratory pathways and fates of cells born in the l ateral and medial ganglionic eminences (LGE and MGE) in 13.5-day-old mouse embryos. We demonstrate that LGE and MGE cells migrate along different rout es to populate distinct regions in the developing brain. We show that LGE c ells migrate ventrally and anteriorly, and give rise to the projecting medi um spiny neurons in the striatum, nucleus accumbens and olfactory tubercle, and to granule and periglomerular cells in the olfactory bulb. By contrast , we show that the NIGE is a major source of neurons migrating dorsally and invading the developing neocortex. MGE cells migrate into the neocortex vi a the neocortical subventricular zone and differentiate into the transient subpial granule neurons in the marginal zone and into a stable population o f GABA-, parvalbumin- or somatostatin-expressing interneurons throughout th e cortical plate.