[Show abstract][Hide abstract] ABSTRACT: The adult mouse subependymal zone (SEZ) harbors neural stem cells that are thought to exclusively generate GABAergic interneurons of the olfactory bulb. We examined the adult generation of glutamatergic juxtaglomerular neurons, which had dendritic arborizations that projected into adjacent glomeruli, identifying them as short-axon cells. Fate mapping revealed that these originate from Neurog2- and Tbr2-expressing progenitors located in the dorsal region of the SEZ. Examination of the progenitors of these glutamatergic interneurons allowed us to determine the sequential expression of transcription factors in these cells that are thought to be hallmarks of glutamatergic neurogenesis in the developing cerebral cortex and adult hippocampus. Indeed, the molecular specification of these SEZ progenitors allowed for their recruitment into the cerebral cortex after a lesion was induced. Taken together, our data indicate that SEZ progenitors not only produce a population of adult-born glutamatergic juxtaglomerular neurons, but may also provide a previously unknown source of progenitors for endogenous repair.
[Show abstract][Hide abstract] ABSTRACT: Little is known of the transcription factors expressed by adult neural progenitors produced in the hippocampal neurogenic niche. Here, we study the expression of the proneural basic helix-loop-helix (bHLH) transcription factor Neurogenin-2 (Ngn2) in the adult hippocampus. We have characterized the pattern of expression of Ngn2 in the adult hippocampus using immunostaining for Ngn2 protein and a Ngn2-green fluorescent protein (GFP) reporter mouse strain. A significant proportion of Ngn2-expressing cells were mitotically active. Ngn2-GFP expression was restricted to the subgranular zone and declined with age. Neuronal markers were used to determine the phenotype of Ngn2-expressing cells. The vast majority of Ngn2-GFP-positive cells expressed the immature neuronal markers, doublecortin (DCX) and polysialic acid-neural cell adhesion molecule (PSA-NCAM). Finally, the pattern of Ngn2 expression was studied following seizure induction. Our data show an increase in neurogenesis, detected in these animals by bromodeoxyuridine (BrdU) and DCX staining that was contemporaneous with a marked increase in Ngn2-GFP-expression. Taken together, our results show that Ngn2-GFP represents a specific marker for neurogenesis and its modulation in the adult hippocampus. Ngn2 transient expression in proliferating neuronal progenitors supports the idea that it plays a significant role in adult neurogenesis.
European Journal of Neuroscience 06/2007; 25(9):2591-603. DOI:10.1111/j.1460-9568.2007.05541.x · 3.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The dentate gyrus continues to produce new granule cells throughout life. Understanding the mechanisms underlying their integration into the pre-existing hippocampal circuitry is of crucial importance. In the present study, we developed an approach allowing visual tracking of newborn granule cells in hippocampal organotypic slices. By crossing neurogenin 2 (Ngn2-CreER) with Cre-reporter mice expressing YFP or GFP reporter genes, it was possible to observe living cells after treating slice cultures with 4-hydroxytamoxifen to induce Cre recombinase activation. Colocalization of GFP with the mitotic marker BrdU demonstrated that the GFP-expressing granule cells were born in vitro. They mature and integrate normally into the hippocampal circuitry, as shown using morphological and electrophysiological techniques. This ex vivo approach therefore offers a highly accessible model to study the effects of long-term treatments on maturation and integration of newborn granule cells.