Tis21 is required for adult neurogenesis in the subventricular zone and for olfactory behavior regulating cyclins, BMP4, Hes1/5 and Ids.

Stefano Farioli-Vecchioli,Irene Cinã,Manuela Ceccarelli,Laura Micheli,Luca Leonardi,Marco Costanzi,Vincenzo Cestari,Andrea Mattera,Sara Cannas,Raffaella Scardigli,Daniele Saraulli,Felice Tirone,Francesca Dâ€™Alessandro

doi:10.3389/fncel.2014.00098

Abstract

Bone morphogenic proteins (BMPs) and the Notch pathway regulate quiescence and self-renewal of stem cells of the subventricular zone (SVZ), an adult neurogenic niche. Here we analyze the role at the intersection of these pathways of Tis21 (Btg2/PC3), a gene regulating proliferation and differentiation of adult SVZ stem and progenitor cells. In Tis21-null SVZ and cultured neurospheres, we observed a strong decrease in the expression of BMP4 and its effectors Smad1/8, while the Notch anti-neural mediators Hes1/5 and the basic helix-loop-helix (bHLH) inhibitors Id1-3 increased. Consistently, expression of the proneural bHLH gene NeuroD1 decreased. Moreover, cyclins D1/2, A2, and E were strongly up-regulated. Thus, in the SVZ Tis21 activates the BMP pathway and inhibits the Notch pathway and the cell cycle. Correspondingly, the Tis21-null SVZ stem cells greatly increased; nonetheless, the proliferating neuroblasts diminished, whereas the post-mitotic neuroblasts paradoxically accumulated in SVZ, failing to migrate along the rostral migratory stream to the olfactory bulb. The ability, however, of neuroblasts to migrate from SVZ explants was not affected, suggesting that Tis21-null neuroblasts do not migrate to the olfactory bulb because of a defect in terminal differentiation. Notably, BMP4 addition or Id3 silencing rescued the defective differentiation observed in Tis21-null neurospheres, indicating that they mediate the Tis21 pro-differentiative action. The reduced number of granule neurons in the Tis21-null olfactory bulb led to a defect in olfactory detection threshold, without effect on olfactory memory, also suggesting that within olfactory circuits new granule neurons play a primary role in odor sensitivity rather than in memory.

Highlights

The subventricular zone (SVZ) of the lateral ventricles is one of the two neurogenic niches, together with the dentate gyrus of the hippocampus, where new neurons are continuously generated throughout adulthood (Zhao et al, 2008)
A parallel analysis of mRNA expression was performed on neurosphere cultures derived from the neural stem cells isolated from the SVZ of P60 mice, as previously described (Farioli-Vecchioli et al, 2012a)
In the SVZ we analyzed the expressions of the basic helix-loop-helix (bHLH) pro-neural genes NeuroD1, which is necessary for the differentiation of SVZ neurons (Gao et al, 2009), and Mash1, which is expressed in transient amplifying progenitor cells and is required for the generation of both neurons and oligodendrocytes (Parras et al, 2004)

Summary

Introduction

The subventricular zone (SVZ) of the lateral ventricles is one of the two neurogenic niches, together with the dentate gyrus of the hippocampus, where new neurons are continuously generated throughout adulthood (Zhao et al, 2008). According to a prevailing hypothesis, the new neurons in the SVZ are generated by resident radial glia-like cells that represent quiescent neural stem cells (reviewed by Alvarez-Buylla and Lim, 2004). These are a glial fibrillary acidic protein-positive (GFAP) subset of astrocytes, termed type B cells (Doetsch et al, 1999), which give rise to rapidly proliferating transient amplifying cells which are GFAP-negative and express the transcription factors of the Dlx family (type C cells; Doetsch et al, 2002). A possibility which reconciles these views is that BMPs are required to maintain quiescence as well as self-renewal of SVZ stem cells, as observed in the dentate gyrus (Mira et al, 2010)

Methods

Results

Conclusion