Proliferation of Murine Midbrain Neural Stem Cells Depends upon an Endogenous Sonic Hedgehog (Shh) Source

Abstract

The Sonic Hedgehog (Shh) pathway is responsible for critical patterning events early in development and for regulating the delicate balance between proliferation and differentiation in the developing and adult vertebrate brain. Currently, our knowledge of the potential role of Shh in regulating neural stem cells (NSC) is largely derived from analyses of the mammalian forebrain, but for dorsal midbrain development it is mostly unknown. For a detailed understanding of the role of Shh pathway for midbrain development in vivo, we took advantage of mouse embryos with cell autonomously activated Hedgehog (Hh) signaling in a conditional Patched 1 (Ptc1) mutant mouse model. This animal model shows an extensive embryonic tectal hypertrophy as a result of Hh pathway activation. In order to reveal the cellular and molecular origin of this in vivo phenotype, we established a novel culture system to evaluate neurospheres (nsps) viability, proliferation and differentiation. By recreating the three-dimensional (3-D) microenvironment we highlight the pivotal role of endogenous Shh in maintaining the stem cell potential of tectal radial glial cells (RGC) and progenitors by modulating their Ptc1 expression. We demonstrate that during late embryogenesis Shh enhances proliferation of NSC, whereas blockage of endogenous Shh signaling using cyclopamine, a potent Hh pathway inhibitor, produces the opposite effect. We propose that canonical Shh signaling plays a central role in the control of NSC behavior in the developing dorsal midbrain by acting as a niche factor by partially mediating the response of NSC to epidermal growth factor (EGF) and fibroblast growth factor (FGF) signaling. We conclude that endogenous Shh signaling is a critical mechanism regulating the proliferation of stem cell lineages in the embryonic dorsal tissue.

Sonic hedgehog (SHH) signaling improves the angiogenic potential of Wharton’s jelly-derived mesenchymal stem cells (WJ-MSC)

“…Furthermore, the use of 5E1 as a blocking antibody allows us to conclude that WJ-MSC display basal SHH pathway activity in vitro as evidenced by PTCH1 and GLI1 modulation. Our results suggest that WJ-MSC display SHH autocrine or paracrine signaling as shown already for MSC in other niches [ 97 – 100 ]. However, we must keep in mind that there seems to be a subpopulation of SHH-positive cells within the WJ.…”

Sonic Hedgehog modulates EGFR dependent proliferation of neural stem cells during late mouse embryogenesis through EGFR transactivation

“…This potentiates the mitogenic effects of low EGF concentrations. Taking into account the recently described Shh constitutive autocrine modulation in NSCs (Bigelow et al, 2005; Ruiz i Altaba et al, 2007; Martínez et al, 2013), our results suggest that downstram activation of EGFR might provide the necessary strength to the intracellular pathways to mount a mitogenic response in NSCs. This might eventually increase the expression of EGFR, as previously reported for other EGFR transactivating receptors (Buvinic et al, 2007).…”

Morphogenetic and Histogenetic Roles of the Temporal-Spatial Organization of Cell Proliferation in the Vertebrate Corticogenesis as Revealed by Inter-specific Analyses of the Optic Tectum Cortex Development

“…Shh also exhibits a versatile role, acting as a morphogen in the ventral basal plate ( Li et al, 2005 ; Bayly et al, 2007 ) and as a mitogen in the midbrain dorsal alar plate ( Agarwala et al, 2001 ; Feijóo et al, 2011 ; Rapacioli et al, 2012a ; Martínez et al, 2013 ). Shh exhibits several developmental roles in the midbrain and metencephalon (r1) primordia and their derivatives (OT and cerebellum respectively; Dahmane and Ruiz i Altaba, 1999 ).…”