Persistent expression of stabilized β-catenin delays maturation of radial glial cells into intermediate progenitors

Abstract

Transgenic mice expressing stabilized beta-catenin in neural progenitors develop enlarged brains resulting from increased progenitor expansion. To more precisely define beta-catenin regulation of progenitor fate, we employed a conditional transgenic approach to delete the beta-catenin regulatory domain from neural progenitors, resulting in expression of stabilized protein from its endogenous promoter in these cells and their progeny. An increased fraction of transgenic cortical cells express the progenitor markers Nestin and LewisX, confirming a relative expansion of this population. Sustained beta-catenin activity expands RC2 and Pax6 expression in the developing cortex while postponing the onset of Tbr2 expression, suggesting a delay in maturation of radial glia into intermediate progenitors. Furthermore, transgenic cortical cells fail to either upregulate ErbB4 or develop a mitogenic response to epidermal growth factor, changes that normally accompany the acquisition of an intermediate fate. Likewise, transgenic brains do not develop a distinct subventricular zone or superficial cortical layers, and overexpression of stabilized beta-catenin by in utero electroporation caused a relative reduction of upper layer vs. lower layer cortical neurons, indicating that persistent beta-catenin activity interferes with the generation of progenitors responsible for the production of upper layer cortical neurons. Collectively, these findings demonstrate that beta-catenin functions to maintain the radial glial population, and suggest that downregulation of beta-catenin signaling may be critical to facilitate the transition to an intermediate progenitor phenotype.

Neural progenitor cells orchestrate microglia migration and positioning into the developing cortex

“…To functionally validate the close relationship between BP generation and microglia recruitment into the VZ/SVZ, we next assessed whether defective neurogenesis might influence Iba1 þ cell recruitment or positioning into the cerebral cortex. We first analysed Gfap Cre /b-Catenin Ex3 mice owing to their propensity to express a stabilized and constitutive active form of b-catenin in cortical RG leading to a dramatic impairment of Tbr2 þ cell generation 29,30 . At E14.5 the expression of Cxcl12 was almost completely abolished in the cortical SVZ of Gfap Cre /b-Catenin Ex3 mice (Fig.…”

“…In mice carrying a constitutive active form of b-Catenin 46 in RG-a genetic alteration that prevents RG to acquire the BP phenotype and to differentiate into Tbr2 þ cells 29,30,47 -the reduction of BP affected Cxcl12 expression in the SVZ and the number of microglia was reduced to B60%. In Pax6 Sey/Sey mice, carrying a null allele for the transcription factor Pax6, Tbr2 þ cells were greatly reduced, Cxcl12 expression was suppressed into the SVZ 6 and a significant reduction of microglia was observed.…”

Non-muscle Mlck is required for β-catenin- and FoxO1-dependent downregulation of Cldn5 in IL-1β-mediated barrier dysfunction in brain endothelial cells

“…Ectopic expression of nmMlck was achieved by using an untagged plasmid (pCMV6 vector) containing the full-length cDNA for the mouse Mylk gene (Origene Technologies, MD). Ectopic expression of transcriptionally active bcatenin (Wrobel et al, 2007) was achieved by using a plasmid (pCAG-GFP vector) containing a mutated Ctnnb1 gene (encoding a protein with a deletion of the first 90 amino acids of b-catenin, Addgene plasmid 26645; Addgene, MA). The introduction of siRNA duplexes and plasmids was achieved using the Nucleofector kit (Amaxa Biosystems, MD).…”

Wnt signaling and its downstream target N-myc regulate basal progenitors in the developing neocortex

“…It is therefore of great interest to elucidate which progenitor populations and which steps in neuron production are being affected by this pathway. Accumulating evidence suggests that activation of the Wnt--catenin pathway promotes proliferation of neural precursor cells (NPCs) that include apical progenitors and basal progenitors (Chenn and Walsh, 2002;Woodhead et al, 2006;Wrobel et al, 2007;Zechner et al, 2003). For instance, persistent expression of a stabilized form of -catenin in NPCs results in an enlarged brain accompanied by excess proliferation of NPCs, presumably due to increased cell cycle re-entry (Chenn and Walsh, 2002;Wrobel et al, 2007).…”

“…Accumulating evidence suggests that activation of the Wnt--catenin pathway promotes proliferation of neural precursor cells (NPCs) that include apical progenitors and basal progenitors (Chenn and Walsh, 2002;Woodhead et al, 2006;Wrobel et al, 2007;Zechner et al, 2003). For instance, persistent expression of a stabilized form of -catenin in NPCs results in an enlarged brain accompanied by excess proliferation of NPCs, presumably due to increased cell cycle re-entry (Chenn and Walsh, 2002;Wrobel et al, 2007). In addition to the proliferation-stimulating roles of Wnt signaling, it has been shown that the Wnt--catenin pathway instructs neuronal differentiation of NPCs during neocortical development (Guillemot, 2007;Hirabayashi et al, 2004;Israsena et al, 2004;Lyu et al, 2008;Muroyama et al, 2004;Zhou et al, 2006).…”