NFIX Regulates Neural Progenitor Cell Differentiation During Hippocampal Morphogenesis

Cerebral Cortex January 2014;24:261–279 doi:10.1093/cercor/bhs307 Advance Access publication October 4, 2012 NFIX Regulates Neural Progenitor Cell Differentiation During Hippocampal Morphogenesis Yee Hsieh Evelyn Heng1, Robert C. McLeay3, Tracey J. Harvey1, Aaron G. Smith1, Guy Barry2, Kathleen Cato1, Céline Plachez4, Erica Little2, Sharon Mason2, Chantelle Dixon1, Richard M. Gronostajski5, Timothy L. Bailey3, Linda J. Richards1,2 and Michael Piper1,2 1 The School of Biomedical Sciences, 2Queensland Brain Institute, 3Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia, 4School of Medicine, The University of Maryland, Baltimore, MD, USA and 5 Department of Biochemistry and the Program in Neuroscience, Developmental Genomics Group, New York State Center of Excellence in Bioinformatics and Life Sciences, State University of New York at Buffalo, Buffalo, NY, USA Address correspondence to M. Piper, The School of Biomedical Sciences and the Queensland Brain Institute, The University of Queensland, Brisbane 4072, Queensland, Australia. Email: Keywords: glia, glial fibrillary acidic protein, neural progenitor cell, nuclear factor one X, SOX9 Introduction During nervous system formation, one of the most important developmental events to occur is the differentiation of neural progenitor cells into neurons and glia. The embryonic forebrain provides a cogent example of this, with neural progenitor cells within the proliferative ventricular zone, region executing a program of proliferation, then differentiation, to generate the postmitotic cells of the cortex and hippocampus (Sauvageot and Stiles 2002). The abnormal proliferation or differentiation of cortical neural progenitor cells during development can lead to severe functional consequences, such as lissencephaly and microcephaly, both of which can cause mental retardation (Manzini and Walsh 2011). As such, understanding the regulatory processes controlling whether neural progenitor cells either divide and self-renew or exit the cell cycle and differentiate is critical to our understanding of both normal and pathological cortical development. A number of recent studies have begun to elucidate some of the key molecules and signaling pathways that control how neural progenitor cell proliferation and differentiation is © The Author 2012. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: coordinated during development. Examples include the Notch (Shimojo et al. 2008; Imayoshi et al. 2010), fibroblast growth factor (Sahara and O’Leary 2009; Rash et al. 2011), and Sonic hedgehog (SHH; Komada et al. 2008) signaling pathways, all of which have been implicated in regulating progenitor cell identity during development of the cortex. Transcription factors of the Sry-related HMG box (SOX) family have also been shown to play a role in the maintenance of progenitor cell identity (Stolt and Wegner 2010). For instance, both SOX2 and SOX3 are expressed by neural progenitor cells within the developing and adult forebrain (Avilion et al. 2003; Wang et al. 2006), and SOX2 has been implicated in maintaining progenitor cell identity within the developing neocortex (Bani-Yaghoub et al. 2006) and the adult hippocampus (Suh et al. 2007). Another suite of molecules known to play a role in regulating the differentiation of neural progenitor cells are the transcription factors of the Nuclear factor one (NFI) family (Piper et al. 2007; Mason et al. 2009), which in vertebrates comprises 4 members; Nfia, Nfib, Nfic, and Nfix (Rupp et al. 1990; Kruse et al. 1991). Mice lacking either Nfia or Nfib display neurological phenotypes including dysgenesis of the corpus callosum (Shu, Butz, et al. 2003; Shu, Puche, et al. 2003; Piper, Moldrich, et al. 2009; Piper, Plachez, et al. 2009), hippocampal malformation (Barry et al. 2008; Piper et al. 2010), and delays in cerebellar development (SteelePerkins et al. 2005; Wang et al. 2007). Mechanistically, Nfi genes have been implicated in regulating glial development via promoting the expression of astrocyte-specific genes (Gopalan et al. 2006; Brun et al. 2009), and Nfia and Nfib were recently shown to promote progenitor cell differentiation in a complementary fashion within the developing telencephalon through the repression of the Notch signaling pathway (Piper et al. 2010). Nfix−/− mice also display severe neurological phenotypes (Driller et al. 2007; Campbell et al. 2008), and NFIX has previously been implicated in driving the expression of astrocytic genes during neural development (Gopalan et al. 2006; Piper et al. 2011). However, the mechanism by which NFIX regulates morphogenesis of the nervous system in vivo remains undefined. Here, using the developing hippocampus of Nfix−/− mice as a model, we reveal that NFIX regulates the differentiation of neural progenitor cells through the transcriptional regulation of progenitor-specific pathways. Our data demonstrate that Nfix −/− mice display delayed progenitor cell differentiation, which culminates in deficits in both neuronal and glial formation. Moreover, the formation of progenitor cells within the postnatal dentate gyrus is abnormal in Nfix −/− 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. mice. Finally, we show that SOX9, a central mediator of progenitor cell self-renewal that acts downstream of SHH signaling during corticogenesis (Scott et al. 2010), is a target for transcriptional repression by NFIX. Taken together, these data reveal a central role for NFIX in orchestrating the timely differentiation of neural progenitor cells within the embry (...truncated)