Rapid genetic targeting of pial surface neural progenitors and immature neurons by neonatal electroporation

Abstract

BackgroundRecent findings have indicated the presence of a progenitor domain at the marginal zone/layer 1 of the cerebral cortex, and it has been suggested that these progenitors have neurogenic and gliogenic potential. However, their contribution to the histogenesis of the cortex remains poorly understood due to difficulties associated with genetically manipulating these unique cells in a population-specific manner.ResultsWe have adapted the electroporation technique to target pial surface cells for rapid genetic manipulation at postnatal day 2. In vivo data show that most of these cells proliferate and progressively differentiate into both neuronal and glial subtypes. Furthermore, these cells localize to the superficial layers of the optic tectum and cerebral cortex prior to migration away from the surface.ConclusionsWe provide a foundation upon which future studies can begin to elucidate the molecular controls governing neural progenitor fate, migration, differentiation, and contribution to cortical and tectal histogenesis. Furthermore, specific genetic targeting of such neural progenitor populations will likely be of future clinical interest.

Noncanonical Sites of Adult Neurogenesis in the Mammalian Brain

“…Interestingly, Tamura and colleagues found that a subpopulation of NG2 þ /DCX þ (doublecortin) cells resides in the rat neocortex, some of which could acquire neuronal specification (Tamura et al 2007). Neuronal progenitors have also been described in cortical layer 1 of neonatal (Breunig et al 2012) as well as adult rats (Ohira et al 2010), wherein they increase 1.6-fold after mild ischemia. No clear evidence of spontaneous neurogenesis has been shown in the intact mouse (as opposed to rat) cerebral cortex, thus confirming the importance of the animal species in parenchymal neurogenesis (see Table 1) and the possible differences existing in cortical structural plasticity when comparing rats and mice.…”

“…To further complicate the picture is the existence of glial progenitors retaining proliferative capacity in wide areas of the mature CNS (reviewed in Dawson et al 2000;Butt et al 2005;Nishiyama et al 2009;Trotter et al 2010). The largest class of these cells express NG2 (Horner et al 2000) and are often referred to simply as NG2 cells.…”

“…The largest class of these cells express NG2 (Horner et al 2000) and are often referred to simply as NG2 cells. They are also called synantocytes (Butt et al 2005) or polydendrocytes (Nishiyama et al 2009), and are morphologically, antigenically, and functionally distinct from mature astrocytes, oligodendrocytes, and microglia. NG stands for neuron-glia, and NG2 þ cells can express neuronal markers during differentiation (see Crociara et al 2013) leading to confusion and perhaps erroneous data interpretation in the literature.…”

Neonatal Pial Surface Electroporation

“…In large part, this has been due to the development of increasingly precise genetic tools, such as nervous system specific Cre recombination of floxed alleles or retroviral lineage tracing 4 . However, one progenitor region-the pial surface progenitor zone-has only recently been described in any detail [5][6][7] and awaits comprehensive examination.…”

“…In the adult brain, it has been reported that interneurons can be born from pial surface progenitors following hypoxic challenge 7 . However, the contribution of this region to his to genensis during embryonic and postnatal development has remained obscure in part due to the difficulty of specifically investigating this region 6 . In the superior colliculus and in the cerebral cortex, superficial (or layer I in the cortex) interneurons may modulate the circuit output of underlying excitatory neuron populations and thus contribute significantly to the function of these structures.…”