NFIX Regulates Neural Progenitor Cell Differentiation During Hippocampal Morphogenesis

Abstract

Neural progenitor cells have the ability to give rise to neurons and glia in the embryonic, postnatal and adult brain. During development, the program regulating whether these cells divide and self-renew or exit the cell cycle and differentiate is tightly controlled, and imbalances to the normal trajectory of this process can lead to severe functional consequences. However, our understanding of the molecular regulation of these fundamental events remains limited. Moreover, processes underpinning development of the postnatal neurogenic niches within the cortex remain poorly defined. Here, we demonstrate that Nuclear factor one X (NFIX) is expressed by neural progenitor cells within the embryonic hippocampus, and that progenitor cell differentiation is delayed within Nfix(-/-) mice. Moreover, we reveal that the morphology of the dentate gyrus in postnatal Nfix(-/-) mice is abnormal, with fewer subgranular zone neural progenitor cells being generated in the absence of this transcription factor. Mechanistically, we demonstrate that the progenitor cell maintenance factor Sry-related HMG box 9 (SOX9) is upregulated in the hippocampus of Nfix(-/-) mice and demonstrate that NFIX can repress Sox9 promoter-driven transcription. Collectively, our findings demonstrate that NFIX plays a central role in hippocampal morphogenesis, regulating the formation of neuronal and glial populations within this structure.

Transcriptional regulation of intermediate progenitor cell generation during hippocampal development

“…Previous studies have demonstrated that neural progenitor cells in the hippocampal neuroepithelium express NFIX during development from at least E13.5 onwards (Heng et al, 2014); however, the cell type-specific identity of these cells has not been established. The transition of radial glia to IPCs during development is demarcated by the sequential expression of PAX6 then TBR2 (EOMES) (Englund et al, 2005).…”

“…We have previously reported elevated numbers of PAX6 + cells (indicative of increased numbers of radial glial cells) and delayed neuronal differentiation in the hippocampus of Nfix −/− mice at E16.5 (Heng et al, 2014). It remained unclear, however, when these developmental defects first become apparent and which stage of the lineage transition from a stem cell to a mature neuron is affected in these mice.…”

“…Mice lacking Nfix exhibit markedly reduced numbers of astrocytes throughout the embryonic cerebral cortex and cerebellum (Piper et al, 2011;Heng et al, 2014). In addition to promoting astrocyte lineage progression, individual Nfi knockout mice also exhibit elevated numbers of progenitor cells and delayed expression of neuronal markers within the ammonic neuroepithelium of the presumptive hippocampus during embryonic development (Piper et al, 2010(Piper et al, , 2014Heng et al, 2014).…”

Epigenomic enhancer annotation reveals a key role for NFIX in neural stem cell quiescence

“…Thus, NFIX is expressed by a subset of quiescent NSCs in vivo and might play a similar role in regulating their gene expression programs, as we observed in cultured quiescent NS cells. Nfix-null mutant mice present severe morphological defects in both the SEZ and DG at postnatal stages as well as defects in progenitor cell differentiation in the DG at birth (Campbell et al 2008;Heng et al 2012b). They die at 3 wk of age, which precludes an analysis of hippocampal NSCs by label retention, but postnatal hippocampal NSCs can also be identified by their radial morphology and the coexpression of Nestin and GFAP.…”

“…Nfix mutants present an overexpansion of the embryonic brain and a delay of hippocampal progenitor differentiation that are not seen in other Nfi mutants (Driller et al 2007;Campbell et al 2008;Heng et al 2012b). Moreover, manipulation of Nfia expression alongside that of Nfix in NS cells shows that the two genes have different activities in the cells, and Nfia does not have a prominent role in the regulation of quiescence (B Martynoga, unpubl.).…”