Emx1-expressing neural stem cells in the subventricular zone give rise to new interneurons in the ischemic injured striatum.

Neural stem cells from different regions within the subventricular zone (SVZ) are able to produce several different subtypes of interneurons in the olfactory bulb throughout life. Previous studies have shown that ischemic stroke induces the production of new neurons in the damaged striatum from the SVZ. However, the origins and genetic profiles of these newborn neurons remain largely unknown as SVZ neural stem cells are heterogeneous. In the present study, using a mouse model of perinatal hypoxic-ischemic (H/I) brain injury combined with BrdU labeling methods, we found that, as in rat brains, virtually all newborn neuroblasts that migrate from the SVZ into the ischemic injured striatum exclusively express the transcription factor Sp8. Furthermore, although newborn neuroblasts are plentiful in the damaged striatum, only a few can differentiate into calretinin-expressing (CR+) interneurons that continuously express Sp8. Genetic fate mapping reveals that newly born CR+ interneurons are generated from Emx1-expressing neural stem cells in the dorsal-lateral SVZ. These results suggest that the fate of the Emx1-expressing lineage in the ischemic damaged striatum is restricted. However, when Sp8 was conditionally inactivated in the Emx1-lineage cells, Pax6 was ectopically expressed by a subpopulation of Emx1-derived CR+ cells in the normal and damaged striatum. Interestingly, these cells possessed large cell bodies and long processes. This work identifies the origin of the newly born CR+ interneurons in the damaged striatum after ischemic brain injury.