The HECT-domain ubiquitin ligase Huwe1 controls neural differentiation and proliferation by destabilizing the N-Myc oncoprotein

Development of the nervous system requires that timely withdrawal from the cell cycle be coupled with initiation of differentiation. Ubiquitin-mediated degradation of the N-Myc oncoprotein in neural stem/progenitor cells is thought to trigger the arrest of proliferation and begin differentiation. Here we report that the HECT-domain ubiquitin ligase Huwe1 ubiquitinates the N-Myc oncoprotein through Lys 48-mediated linkages and targets it for destruction by the proteasome. This process is physiologically implemented by embryonic stem (ES) cells differentiating along the neuronal lineage and in the mouse brain during development. Genetic and RNA interference-mediated inactivation of the Huwe1 gene impedes N-Myc degradation, prevents exit from the cell cycle by opposing the expression of Cdk inhibitors and blocks differentiation through persistent inhibition of early and late markers of neuronal differentiation. Silencing of N-myc in cells lacking Huwe1 restores neural differentiation of ES cells and rescues cell-cycle exit and differentiation of the mouse cortex, demonstrating that Huwe1 restrains proliferation and enables neuronal differentiation by mediating the degradation of N-Myc. These findings indicate that Huwe1 links destruction of N-Myc to the quiescent state that complements differentiation in the neural tissue

Cloning and characterisation of gripe: a novel interacting partner of e12 during brain development

Deposited with permission of the author. © 2002 Dr. Julian Ik Tsen Heng.The mammalian cerebral cortex is a remarkable product of brain evolution, and is the structure that most distinctively delineates the human species from others (Northcutt and Kaas, 1995; Rakic, 1988). Neurons in the adult brain are organised into cytoarchitectonic areas, defined by distinct biochemical, morphological and physiological characteristics (Rakic 1988). Remarkably, this complex structure is generated from a simple neuroepithelium. What are the signalling mechanisms that direct neuron formation and subsequent functional-parcellation of the cerebral cortex? Key to the study of this process is an understanding of neuronal fate determination. Available evidence demonstrates an intrinsic programming potential by neuronal progenitors within subdomains of the developing cerebral cortex that is instructive for proper corticogenesis. These regional domains are demarcated by expression of certain transcription factors, including members of the Helix-Loop-Helix (HLH) family of proteins. The HLH family of transcription factors are key contributors to a wide array of developmental processes, including neurogenesis and haematopoiesis. These factors are thought to exert their regulatory influences by binding to cognate promoter-DNA sequences as dimers. While studies in mice have convincingly demonstrated that neurogenic HLH proteins such as NeuroD (Lee et al., 1995; Miyata et al., 1999; Liu et al., 2000) and Mash1 (Casarosa et al., 1999) are intimately involved in neuronal fate determination and terminal differentiation, the role of the ubiquitously expressed HLH protein, E12, in mammalian neurogenesis remains ambiguous. Originally discovered as an important regulator of lymphopoiesis, expression studies revealed its widespread expression in proliferative zones of multiple nascent organs of the embryo, including the developing cerebral cortex; implying a role for E12 in development of the nervous system. Since the function of E12 is, in part, coded by its capacity for protein dimerisation, a search was undertaken for binding partners in developing mouse brain, and using a yeast 2-hybrid assay. Yeast 2-hybrid prey libraries were constructed using complementary DNA (cDNA) isolated from embryonic mouse forebrain tissue at early (embryonic day e11.5) and peak (e15.5) stages of neurogenesis. Screening of these libraries for binding partners to an E12 bait resulted in cloning of HLH factors, such as Mash1, NSCL and Id2. Importantly, a novel binding partner, named GRIPE, was cloned as a novel GAP Related Interacting Protein to E12. GRIPE binds to the HLH region of E12, and may require E12 for nuclear import. Furthermore, GRIPE may negatively regulate E12-dependent target gene transcription. High levels of GRIPE and E12 mRNA were coincidently detected during embryogenesis, but only GRIPE mRNA levels remained high in adult brain, particularly in neurons of the cortex and hippocampus. These observations were reconfirmed through an in vitro model of neurogenesis. Taken together, these results indicate that GRIPE is a novel protein whose dimerisation with E12 has important consequences for cells undergoing neuronal differentiation. A model is proposed to suggest how neurogenic HLH proteins that dimerise to E12 may promote signalling cascades driving early neuroblast differentiation

Insights into the Biology and Therapeutic Applications of Neural Stem Cells

The cerebral cortex is essential for our higher cognitive functions and emotional reasoning. Arguably, this brain structure is the distinguishing feature of our species, and yet our remarkable cognitive capacity has seemingly come at a cost to the regenerative capacity of the human brain. Indeed, the capacity for regeneration and neurogenesis of the brains of vertebrates has declined over the course of evolution, from fish to rodents to primates. Nevertheless, recent evidence supporting the existence of neural stem cells (NSCs) in the adult human brain raises new questions about the biological significance of adult neurogenesis in relation to ageing and the possibility that such endogenous sources of NSCs might provide therapeutic options for the treatment of brain injury and disease. Here, we highlight recent insights and perspectives on NSCs within both the developing and adult cerebral cortex. Our review of NSCs during development focuses upon the diversity and therapeutic potential of these cells for use in cellular transplantation and in the modeling of neurodevelopmental disorders. Finally, we describe the cellular and molecular characteristics of NSCs within the adult brain and strategies to harness the therapeutic potential of these cell populations in the treatment of brain injury and disease

Bacurd2 is a novel interacting partner to Rnd2 which controls radial migration within the developing mammalian cerebral cortex.

BACKGROUND: During fetal brain development in mammals, newborn neurons undergo cell migration to reach their appropriate positions and form functional circuits. We previously reported that the atypical RhoA GTPase Rnd2 promotes the radial migration of mouse cerebral cortical neurons (Nature 455(7209):114-8, 2008; Neuron 69(6):1069-84, 2011), but its downstream signalling pathway is not well understood. RESULTS: We have identified BTB-domain containing adaptor for Cul3-mediated RhoA degradation 2 (Bacurd2) as a novel interacting partner to Rnd2, which promotes radial migration within the developing cerebral cortex. We find that Bacurd2 binds Rnd2 at its C-terminus, and this interaction is critical to its cell migration function. We show that forced expression or knockdown of Bacurd2 impairs neuronal migration within the embryonic cortex and alters the morphology of immature neurons. Our in vivo cellular analysis reveals that Bacurd2 influences the multipolar-to-bipolar transition of radially migrating neurons in a cell autonomous fashion. When we addressed the potential signalling relationship between Bacurd2 and Rnd2 using a Bacurd2-Rnd2 chimeric construct, our results suggest that Bacurd2 and Rnd2 could interact to promote radial migration within the embryonic cortex. CONCLUSIONS: Our studies demonstrate that Bacurd2 is a novel player in neuronal development and influences radial migration within the embryonic cerebral cortex

Correction to: Rp58 and p27kip1 coordinate cell cycle exit and neuronal migration within the embryonic mouse cerebral cortex [Neural Dev. (2017);12:8.] doi: 10.1186/s13064-017-0084-3

© 2018 The Author(s). Correction: After publication of the original article [1] it was realised that there were errors in figures 2a,b,f,g, which arose as a result of preparing figures from data collected and analysed at the same time as the work reported in [2] (Supplementary Figure 1 of [2]). An updated Fig. 2 is included with this Correction

p27(kip1) independently promotes neuronal differentiation and migration in the cerebral cortex

The generation of neurons by progenitor cells involves the tight coordination of multiple cellular activities, including cell cycle exit, initiation of neuronal differentiation, and cell migration. The mechanisms that integrate these different events into a coherent developmental program are not well understood. Here we show that the cyclin-dependent kinase inhibitor p27(Kip1) plays an important role in neurogenesis in the mouse cerebral cortex by promoting the differentiation and radial migration of cortical projection neurons. Importantly, these two functions of p27(Kip1) involve distinct activities, which are independent of its role in cell cycle regulation. p27(Kip1) promotes neuronal differentiation by stabilizing Neurogenin2 protein, an activity carried by the N-terminal half of the protein. p27(Kip1) promotes neuronal migration by blocking RhoA signaling, an activity that resides in its C-terminal half. Thus, p27(Kip1) plays a key role in cortical development, acting as a modular protein that independently regulates and couples multiple cellular pathways contributing to neurogenesis

The atypical Rho GTPase Rnd2 is critical for dentate granule neuron development and anxiety-like behavior during adult but not neonatal neurogenesis

International audienceDespite the central role of Rho GTPases in neuronal development, their functions in adult hippocampal neurogenesis remain poorly explored. Here, by using a retrovirus-based loss-of-function approach in vivo , we show that the atypical Rho GTPase Rnd2 is crucial for the survival, positioning, somatodendritic morphogenesis and functional maturation of adult-born dentate granule neurons. Interestingly, most of these functions are specific to granule neurons generated during adulthood since the deletion of Rnd2 in neonatally-born granule neurons only affects dendritogenesis. In addition, suppression of Rnd2 in adult-born dentate granule neurons increases anxiety-like behaviour whereas its deletion in pups has no such effect, a finding supporting the adult neurogenesis hypothesis of anxiety disorders. Thus, our results provide mechanistic insight into the differential regulation of hippocampal neurogenesis during development and adulthood, and establishes a causal relationship between Rnd2 expression and anxiety

Coupling of cell migration with neurogenesis by proneural bHLH factors

After cell birth, almost all neurons in the mammalian central nervous system migrate. It is unclear whether and how cell migration is coupled with neurogenesis. Here we report that proneural basic helix-loop-helix (bHLH) transcription factors not only initiate neuronal differentiation but also potentiate cell migration. Mechanistically, proneural bHLH factors regulate the expression of genes critically involved in migration, including down-regulation of RhoA small GTPase and up-regulation of doublecortin and p35, which, in turn, modulate the actin and microtubule cytoskeleton assembly and enable newly generated neurons to migrate. In addition, we report that several DNA-binding-deficient proneural genes that fail to initiate neuronal differentiation still activate migration, whereas a different mutation of a proneural gene that causes a failure in initiating cell migration still leads to robust neuronal differentiation. Collectively, these data suggest that transcription programs for neurogenesis and migration are regulated by bHLH factors through partially distinct mechanisms