Early postnatal in vivo gliogenesis from nestin-lineage progenitors requires Cdk5

The early postnatal period is a unique time of brain development, as diminishing amounts of neurogenesis coexist with waves of gliogenesis. Understanding the molecular regulation of early postnatal gliogenesis may provide clues to normal and pathological embryonic brain ontogeny, particularly in regards to the development of astrocytes and oligodendrocytes. Cyclin dependent kinase 5 (Cdk5) contributes to neuronal migration and cell cycle control during embryogenesis, and to the differentiation of neurons and oligodendrocytes during adulthood. However, Cdk5’s function in the postnatal period and within discrete progenitor lineages is unknown. Therefore, we selectively removed Cdk5 from nestin-expressing cells and their progeny by giving transgenic mice (nestin-CreERT2/R26R-YFP/CDK5flox/flox [iCdk5] and nestin-CreERT2/R26R-YFP/CDK5wt/wt [WT]) tamoxifen during postnatal (P) days P2-P 4 or P7-P 9, and quantified and phenotyped recombined (YFP+) cells at P14 and P21. When Cdk5 gene deletion was induced in nestin-expressing cells and their progeny during the wave of cortical and hippocampal gliogenesis (P2-P4), significantly fewer YFP+ cells were evident in the cortex, corpus callosum, and hippocampus. Phenotypic analysis revealed the cortical decrease was due to fewer YFP+ astrocytes and oligodendrocytes, with a slightly earlier influence seen in oligodendrocytes vs. astrocytes. This effect on cortical gliogenesis was accompanied by a decrease in YFP+ proliferative cells, but not increased cell death. The role of Cdk5 in gliogenesis appeared specific to the early postnatal period, as induction of recombination at a later postnatal period (P7-P9) resulted in no change YFP+ cell number in the cortex or hippocampus. Thus, glial cells that originate from nestin-expressing cells and their progeny require Cdk5 for proper development during the early postnatal period

B Cells Migrate into Remote Brain Areas and Support Neurogenesis and Functional Recovery after Focal Stroke in Mice

Lymphocytes infiltrate the stroke core and penumbra and often exacerbate cellular injury. B cells, however, are lymphocytes that do not contribute to acute pathology but can support recovery. B cell adoptive transfer to mice reduced infarct volumes 3 and 7 d after transient middle cerebral artery occlusion (tMCAo), independent of changing immune populations in recipient mice. Testing a direct neurotrophic effect, B cells cocultured with mixed cortical cells protected neurons and maintained dendritic arborization after oxygen-glucose deprivation. Whole-brain volumetric serial two-photon tomography (STPT) and a custom-developed image analysis pipeline visualized and quantified poststroke B cell diapedesis throughout the brain, including remote areas supporting functional recovery. Stroke induced significant bilateral B cell diapedesis into remote brain regions regulating motor and cognitive functions and neurogenesis (e.g., dentate gyrus, hypothalamus, olfactory areas, cerebellum) in the whole-brain datasets. To confirm a mechanistic role for B cells in functional recovery, rituximab was given to human CD20+ (hCD20+) transgenic mice to continuously deplete hCD20+-expressing B cells following tMCAo. These mice experienced delayed motor recovery, impaired spatial memory, and increased anxiety through 8 wk poststroke compared to wild type (WT) littermates also receiving rituximab. B cell depletion reduced stroke-induced hippocampal neurogenesis and cell survival. Thus, B cell diapedesis occurred in areas remote to the infarct that mediated motor and cognitive recovery. Understanding the role of B cells in neuronal health and disease-based plasticity is critical for developing effective immune-based therapies for protection against diseases that involve recruitment of peripheral immune cells into the injured brain

Inducible knockout of Mef2a, -c, and -d from nestin-expressing stem/progenitor cells and their progeny unexpectedly uncouples neurogenesis and dendritogenesis in vivo

Myocyte enhancer factor (Mef)‐2 transcription factors are implicated in activity‐dependent neuronal processes during development, but the role of MEF2 in neural stem/progenitor cells (NSPCs) in the adult brain is unknown. We used a transgenic mouse in which Mef2a, ‐c, and ‐d were inducibly deleted in adult nestin‐expressing NSPCs and their progeny. Recombined cells in the hippocampal granule cell layer were visualized and quantified by yellow fluorescent protein (YFP) expression. In control mice, postmitotic neurons expressed Mef2a, ‐c, and ‐d, whereas type 1 stem cells and proliferating progenitors did not Based on this expression, we hypothesized that Mef2a, ‐c, and ‐d deletion in adult nestin‐expressing NSPCs and their progeny would result in fewer mature neurons. Control mice revealed an increase in YFP+ neurons and dendrite formation over time. Contrary to our hypothesis, inducible Mef2 KO mice also displayed an increase in YFP+ neurons over time—but with significantly stunted dendrites—suggesting an uncoupling of neuron survival and dendritogenesis. We also found non‐cell‐autonomous effects after Mef2a, ‐c, and ‐d deletion. These in vivo findings indicate a surprising functional role for Mef2a, ‐c, and ‐d in cell‐ and non‐cell‐autonomous control of adult hippocampal neurogenesis that is distinct from its role during development.—Latchney, S. E., Jiang, Y., Petrik, D. P., Eisch, A. J., Hsieh, J. Inducible knockout of Mef2a, ‐c, and ‐d from nestin‐expressing stem/progenitor cells and their progeny unexpectedly uncouples neurogenesis and dendritogenesis in vivo

Inducible knockout of Mef2a, -c, and -d from nestin-expressing stem/progenitor cells and their progeny unexpectedly uncouples neurogenesis and dendritogenesis in vivo

Myocyte enhancer factor (Mef)‐2 transcription factors are implicated in activity‐dependent neuronal processes during development, but the role of MEF2 in neural stem/progenitor cells (NSPCs) in the adult brain is unknown. We used a transgenic mouse in which Mef2a, ‐c, and ‐d were inducibly deleted in adult nestin‐expressing NSPCs and their progeny. Recombined cells in the hippocampal granule cell layer were visualized and quantified by yellow fluorescent protein (YFP) expression. In control mice, postmitotic neurons expressed Mef2a, ‐c, and ‐d, whereas type 1 stem cells and proliferating progenitors did not Based on this expression, we hypothesized that Mef2a, ‐c, and ‐d deletion in adult nestin‐expressing NSPCs and their progeny would result in fewer mature neurons. Control mice revealed an increase in YFP+ neurons and dendrite formation over time. Contrary to our hypothesis, inducible Mef2 KO mice also displayed an increase in YFP+ neurons over time—but with significantly stunted dendrites—suggesting an uncoupling of neuron survival and dendritogenesis. We also found non‐cell‐autonomous effects after Mef2a, ‐c, and ‐d deletion. These in vivo findings indicate a surprising functional role for Mef2a, ‐c, and ‐d in cell‐ and non‐cell‐autonomous control of adult hippocampal neurogenesis that is distinct from its role during development.—Latchney, S. E., Jiang, Y., Petrik, D. P., Eisch, A. J., Hsieh, J. Inducible knockout of Mef2a, ‐c, and ‐d from nestin‐expressing stem/progenitor cells and their progeny unexpectedly uncouples neurogenesis and dendritogenesis in vivo

Chromatin remodeling factor Brg1 supports the early maintenance and late responsiveness of nestin-lineage adult neural stem and progenitor cells

Insights from embryonic development suggest chromatin remodeling is important in adult neural stem cells (aNSCs) maintenance and self‐renewal, but this concept has not been fully explored in the adult brain. To assess the role of chromatin remodeling in adult neurogenesis, we inducibly deleted Brg1—the core subunit of SWI/SNF‐like Brg1/Brm‐associated factor chromatin remodeling complexes—in nestin‐expressing aNSCs and their progeny in vivo and in culture. This resulted in abnormal adult neurogenesis in the hippocampus, which initially reduced hippocampal aNSCs and progenitor maintenance, and later reduced its responsiveness to physiological stimulation. Mechanistically, deletion of Brg1 appeared to impair cell cycle progression, which is partially due to elevated p53 pathway and p21 expression. Knockdown of p53 rescued the neurosphere growth defects caused by Brg1 deletion. Our results show that epigenetic chromatin remodeling (via a Brg1 and p53/p21‐dependent process) determines the aNSCs and progenitor maintenance and responsiveness of neurogenesis

Chromatin remodeling factor Brg1 supports the early maintenance and late responsiveness of nestin-lineage adult neural stem and progenitor cells

Insights from embryonic development suggest chromatin remodeling is important in adult neural stem cells (aNSCs) maintenance and self‐renewal, but this concept has not been fully explored in the adult brain. To assess the role of chromatin remodeling in adult neurogenesis, we inducibly deleted Brg1—the core subunit of SWI/SNF‐like Brg1/Brm‐associated factor chromatin remodeling complexes—in nestin‐expressing aNSCs and their progeny in vivo and in culture. This resulted in abnormal adult neurogenesis in the hippocampus, which initially reduced hippocampal aNSCs and progenitor maintenance, and later reduced its responsiveness to physiological stimulation. Mechanistically, deletion of Brg1 appeared to impair cell cycle progression, which is partially due to elevated p53 pathway and p21 expression. Knockdown of p53 rescued the neurosphere growth defects caused by Brg1 deletion. Our results show that epigenetic chromatin remodeling (via a Brg1 and p53/p21‐dependent process) determines the aNSCs and progenitor maintenance and responsiveness of neurogenesis

Early postnatal in vivo gliogenesis from nestin-lineage progenitors requires Cdk5

The early postnatal period is a unique time of brain development, as diminishing amounts of neurogenesis coexist with waves of gliogenesis. Understanding the molecular regulation of early postnatal gliogenesis may provide clues to normal and pathological embryonic brain ontogeny, particularly in regards to the development of astrocytes and oligodendrocytes. Cyclin dependent kinase 5 (Cdk5) contributes to neuronal migration and cell cycle control during embryogenesis, and to the differentiation of neurons and oligodendrocytes during adulthood. However, Cdk5’s function in the postnatal period and within discrete progenitor lineages is unknown. Therefore, we selectively removed Cdk5 from nestin-expressing cells and their progeny by giving transgenic mice (nestin-CreERT2/R26R-YFP/CDK5flox/flox [iCdk5] and nestin-CreERT2/R26R-YFP/CDK5wt/wt [WT]) tamoxifen during postnatal (P) days P2-P 4 or P7-P 9, and quantified and phenotyped recombined (YFP+) cells at P14 and P21. When Cdk5 gene deletion was induced in nestin-expressing cells and their progeny during the wave of cortical and hippocampal gliogenesis (P2-P4), significantly fewer YFP+ cells were evident in the cortex, corpus callosum, and hippocampus. Phenotypic analysis revealed the cortical decrease was due to fewer YFP+ astrocytes and oligodendrocytes, with a slightly earlier influence seen in oligodendrocytes vs. astrocytes. This effect on cortical gliogenesis was accompanied by a decrease in YFP+ proliferative cells, but not increased cell death. The role of Cdk5 in gliogenesis appeared specific to the early postnatal period, as induction of recombination at a later postnatal period (P7-P9) resulted in no change YFP+ cell number in the cortex or hippocampus. Thus, glial cells that originate from nestin-expressing cells and their progeny require Cdk5 for proper development during the early postnatal period