Postnatal neurogenesis and gliogenesis in the olfactory bulb from NG2-expressing progenitors of the subventricular zone.

We used a 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP)-enhanced green fluorescent protein (EGFP) transgenic mouse to study postnatal subventricular zone (SVZ) progenitor fate, with a focus on the olfactory bulb (OB). The postnatal OB of the CNP-EGFP mouse contained EGFP+ interneurons and oligodendrocytes. In the anterior SVZ, the majority of EGFP+ progenitors were NG2+. These NG2+/EGFP+ progenitors expressed the OB interneuron marker Er81, the neuroblast markers doublecortin (DC) and Distalless-related homeobox (DLX), or the oligodendrocyte progenitor marker Nkx2.2. In the rostral migratory stream (RMS), EGFP+ cells displayed a migrating phenotype. A fraction of these cells were either NG2-/Er81+/DC+/DLX+ or NG2+/Nkx2.2+. DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) injection into the lateral ventricle (LV) of early postnatal mice demonstrated that NG2+/EGFP+ progenitors migrate from the SVZ through the RMS into the OB. Moreover, fluorescence-activated cell-sorting-purified NG2+/CNP-EGFP+ or NG2+/beta-actin-enhanced yellow fluorescent protein-positive (EYFP+) progenitors transplanted into the early postnatal LV displayed extensive rostral and caudal migration. EYFP+ or EGFP+ graft-derived cells within the RMS were DLX+/Er81+ or Nkx2.2+, migrated to the OB, and differentiated to interneurons and oligodendrocytes. In the subcortical white matter (SCWM), grafted cells differentiated to either oligodendrocytes or astrocytes. Transplantation of NG2+/EYFP+ progenitors selectively purified from the SVZ showed that these cells were migratory and generated glia and neurons in the OB, hippocampus, and striatum. In contrast, cortical, OB, or cerebellar NG2+ cells had a very limited migratory potential and gave rise to glia in the SCWM and striatum. Our findings indicate region-specific differences between NG2+ progenitor cells and show that NG2+ cells can migrate throughout the RMS and contribute to both gliogenesis and neurogenesis in the postnatal OB.