The doublecortin-expressing population in the developing and adult brain contains multipotential precursors in addition to neuronal-lineage cells
Doublecortin (DCX) has recently been promulgated as a selective marker of cells committed to the neuronal lineage in both the developing and the adult brain. To explore the potential of DCX-positive (DCX+) cells more stringently, these cells were isolated by flow cytometry from the brains of transgenic mice expressing green fluorescent protein under the control of the DCX promoter in embryonic, early postnatal, and adult animals. It was found that virtually all of the cells (99.9%) expressing high levels of DCX (DCX high) in the embryonic brain coexpressed the neuronal marker βIII-tubulin and that this population contained no stem-like cells as demonstrated by lack of neurosphere formation in vitro. However, the DCX + population from the early postnatal brain and the adult subventricular zone and hippocampus, which expressed low levels of DCX (DCX low), was enriched for neurosphere-forming cells, with only a small subpopulation of these cells coexpressing the neuronal markers βIII-tubulin or microtubule-associated protein 2. Similarly, the DCXlow population from embryonic day 14 (E14) brain contained neurosphere-forming cells. Only the postnatal cerebellum and adult olfactory bulb contained some DCXhigh cells, which were shown to be similar to the E14 DCX high cells in that they had no stem cell activity. Electrophysiological studies confirmed the heterogeneous nature of DCX + cells, with some cells displaying characteristics of immature or mature neurons, whereas others showed no neuronal characteristics whatsoever. These results indicate that DCXhigh cells, regardless of location, are restricted to the neuronal lineage or are bone fide neurons, whereas some DCXlow cells retain their multipotentiality.