Abstract
The neurogenic niche of the subventricular zone (SVZ) in adult brain tissue takes the form of a pinwheel-like cytoarchitectural structure, with mono-ciliated astrocytes displaying neural stem cell (NSC) characteristics present in the core surrounded by ciliated ependymal cells. For the first time, we have demonstrated the formation of similar pinwheel structures in spinal cord and SVZ tissue-derived neurospheres cultured in vitro. To investigate whether the organization and integrity of these pinwheel structures depends on the appropriate organization of ciliated astrocytes and ependymal cells, we modified neurosphere cell arrangements via the application of the methyltransferase inhibitor 5-aza-2′-deoxycytidine (5-aza-dc) or the antiviral drug ganciclovir (GCV) in transgenic mice expressing herpes simplex virus thymidine kinase from the GFAP promoter (GFAP-TK). Treatment of neurospheres with 5-aza-dc increased FoxJ1 expression, a crucial factor for ciliogenesis, by reducing methylation of the FoxJ1 CpG island. 5-aza-dc also increased the expression of the astrocyte marker GFAP and caused aberrant accumulation of ciliated astrocytes. However, the ablation of dividing astrocytes within neurospheres by GCV treatment led to an increase in the accumulation of ciliated ependymal cells, as evidenced by the increased expression of the ependymal cell markers Vimentin or CD24. While 5-aza-dc and GCV treatment differentially affected cell arrangement, both compounds significantly diminished the number of pinwheel structures present in neurospheres. Thus, we suggest that the ratio of ciliated astrocytes to ependymal cells plays a crucial role in the correct formation of the pinwheel structures in spinal cord tissue-derived neurospheres in vitro.
Highlights
Exploration of the subventricular zone (SVZ) of adult brain tissue has revealed the presence of a pinwheel structure specific to the adult neurogenic niche (Mirzadeh et al, 2008)
We detected astrocyte-like extensions that connected adjacent core centers in neurospheres (Figure 1A, indicated by white arrows in the schematic) similar to those described in the SVZ (Mirzadeh et al, 2008)
We observed regions of small cells delineated by β-catenin (Figure 1B, indicated by continuous white lines in schematic) containing a single basal body detected by γ-tubulin (Figure 1B, an example marked by empty arrowhead), similar to structures usually positioned at the pinwheel structure core identified as astrocytes in the SVZ (Mirzadeh et al, 2008)
Summary
Exploration of the subventricular zone (SVZ) of adult brain tissue has revealed the presence of a pinwheel structure specific to the adult neurogenic niche (Mirzadeh et al, 2008). The pinwheel core consists of mono-ciliated glial fibrillary acidic protein (GFAP)positive astrocyte-like cells that possess properties of neural stem cells (NSCs) surrounded at Pinwheels in Spinal Cord-Derived Neurospheres the periphery by bi- or multi-ciliated ependymal cells. The cilia of astrocytes within the SVZ make contact with the ventricular fluid, and these mono-ciliated cells confer the pinwheel architecture to the ventricular surface in neurogenic regions of the adult brain and may regulate NSC behavior (Mirzadeh et al, 2008). Radial glial cells serve as primary progenitor cells in the CNS and can differentiate into ependymal stem-like cells and astrocytes during early postnatal periods (Jacquet et al, 2009). In addition to ependymal cells, cell subpopulations within the epithelium of the spinal cord central canal, such as dividing GFAP+ astrocytes (Alfaro-Cervello et al, 2012) possess cilia
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