Induction of neural differentiation by the transcription factor neuroD2

PKN1 Is a Novel Regulator of Hippocampal GluA1 Levels

Alterations in the processes that control α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) expression, assembly and trafficking are closely linked to psychiatric and neurodegenerative disorders. We have recently shown that the serine/threonine kinase Protein kinase N1 (PKN1) is a developmentally active regulator of cerebellar synaptic maturation by inhibiting AKT and the neurogenic transcription factor neurogenic differentiation factor-2 (NeuroD2). NeuroD2 is involved in glutamatergic synaptic maturation by regulating expression levels of various synaptic proteins. Here we aimed to study the effect of Pkn1 knockout on AKT phosphorylation and NeuroD2 levels in the hippocampus and the subsequent expression levels of the NeuroD2 targets and AMPAR subunits: glutamate receptor 1 (GluA1) and GluA2/3. We show that PKN1 is expressed throughout the hippocampus. Interestingly, not only postnatal but also adult hippocampal phospho-AKT and NeuroD2 levels were significantly elevated upon Pkn1 knockout. Postnatal and adult Pkn1 ^-/- hippocampi showed enhanced expression of the AMPAR subunit GluA1, particularly in area CA1. Surprisingly, GluA2/3 levels were not different between both genotypes. In addition to higher protein levels, we also found an enhanced GluA1 content in the membrane fraction of postnatal and adult Pkn1 ^-/- animals, while GluA2/3 levels remained unchanged. This points toward a very specific regulation of GluA1 expression and/or trafficking by the novel PKN1-AKT-NeuroD2 axis. Considering the important role of GluA1 in hippocampal development as well as the pathophysiology of several disorders, ranging from Alzheimer's, to depression and schizophrenia, our results validate PKN1 for future studies into neurological disorders related to altered AMPAR subunit expression in the hippocampus.

A stochastic model of adult neurogenesis coupling cell cycle progression and differentiation

Long-term tissue homeostasis requires a precise balance between stem cell self-renewal and the generation of differentiated progeny. Recently, it has been shown that in the adult murine brain, neural stem cells (NSCs) divide mostly symmetrically. This finding suggests that the required balance for tissue homeostasis is accomplished at the population level. However, it remains unclear how this balance is enabled. Furthermore, there is experimental evidence that proneural differentiation factors not only promote differentiation, but also cell cycle progression, suggesting a link between the two processes in NSCs. To study the effect of such a link on NSC dynamics, we developed a stochastic model in which stem cells have an intrinsic probability to progress through cell cycle and to differentiate. Our results show that increasing heterogeneity in differentiation probabilities leads to a decreased probability of long-term tissue homeostasis, and that this effect can be compensated when cell cycle progression and differentiation are positively coupled. Using single-cell RNA-Seq profiling of adult NSCs, we found a positive correlation in the expression levels of cell cycle and differentiation markers. Our findings suggest that a coupling between cell cycle progression and differentiation on the cellular level is part of the process that maintains tissue homeostasis in the adult brain.

Maternal hyperglycemia disturbs neocortical neurogenesis via epigenetic regulation in C57BL/6J mice

Offspring of mothers with hyperglycemia during pregnancy have a higher incidence of long-term neuropsychiatric disorders than offspring from a normal pregnancy, indicating that neocortical neurogenesis might be affected by maternal hyperglycemia. A paucity of study evaluating the effects of hyperglycemia on neocortical neurogenetic differentiation of neural stem cells, and the mechanism remains unclear. We sought to investigate the the roles and possible molecular mechanism of maternal hyperglycemia on neocortical neurogenetic differentiation of neural stem cells. We established a mouse model of a hyperglycemic pregnancy to study effects of intrauterine exposure to maternal hyperglycemia on neocortical neurogenesis. We observed morphological changes in the neocortex and detected the neurogenetic differentiation of neural stem cells in offspring affected by high glucose levels. We investigated the regulatory network between epigenetic modification and transcription factors in differentiated neural stem cells under hyperglycemic conditions. Maternal hyperglycemia disturbs neocortical lamination in some non-malformed offspring. Our results suggested that hyperglycemia altered the early-born neuron fate and the distribution of newborn neurons in deep layers by promoting the earlier differentiation of neural stem cells. Altered histone acetylation and its regulation on the transcription of proneural genes might be correlated to the disrupted differentiation of neural stem cells and altered distribution of newborn projection neurons in the neocortex. Our data raised the possibility that maternal hyperglycemia in pregnancy disturbs the laminar distribution of neocortical projection neurons in some non-malformed offspring via epigenetic regulation on neural stem cell differentiation and the birthdate of neocortical neurons.

CADPS2 gene expression is oppositely regulated by LRRK2 and alpha-synuclein

The Ca²⁺-dependent activator protein for secretion 2 (CADPS2) is a member of the CAPS/CADPS protein family that plays crucial roles in synaptic vesicle dynamics. Genomic variability in the CADPS2 gene has been associated to autism spectrum disorders and Alzheimer's disease, both characterized by altered neurotransmission. Biological evidence also linked CADPS2 to Parkinson's disease (PD), as a disease-causing mutation in leucine-rich repeat kinase 2 (LRRK2) was reported to increase CADPS2 gene and protein expression. Furthermore, restoration of CADPS2 physiologic levels was able to provide neuroprotection in patient-derived neurons, consistent with the synaptic dysfunction postulated to underlie PD. However, little is known about the influence of PD-related proteins on transcriptional regulation of critical synaptic genes such as CADPS2. Here we aimed at investigating the transcriptional effects of LRRK2 and alpha-synuclein (aSyn) on CADPS2 gene expression, using a combination of in silico analyses and cell biology techniques. First, we identified a predicted promoter in the human CADPS2 genomic sequence, which we then utilized in a luciferase-based gene reporter assay. This approach enabled us to disclose a differential effect of high levels of LRRK2 and aSyn on CADPS2 promoter activity. Specifically, CADPS2 transcriptional activity was enhanced by high cellular levels of LRRK2 and reduced by overexpression of aSyn. Consistently, CADPS2 mRNA levels were diminished in aSyn overexpressing cells. Our results indicate that LRRK2 and aSyn participate in the dysregulation of CADPS2 by altering transcription and support the hypothesis that synaptic dysfunctions, through different mechanisms, might contribute to the neuronal defects of diseases such as PD.

Circuit-wide Transcriptional Profiling Reveals Brain Region-Specific Gene Networks Regulating Depression Susceptibility

Depression is a complex, heterogeneous disorder and a leading contributor to the global burden of disease. Most previous research has focused on individual brain regions and genes contributing to depression. However, emerging evidence in humans and animal models suggests that dysregulated circuit function and gene expression across multiple brain regions drive depressive phenotypes. Here, we performed RNA sequencing on four brain regions from control animals and those susceptible or resilient to chronic social defeat stress at multiple time points. We employed an integrative network biology approach to identify transcriptional networks and key driver genes that regulate susceptibility to depressive-like symptoms. Further, we validated in vivo several key drivers and their associated transcriptional networks that regulate depression susceptibility and confirmed their functional significance at the levels of gene transcription, synaptic regulation, and behavior. Our study reveals novel transcriptional networks that control stress susceptibility and offers fundamentally new leads for antidepressant drug discovery.

Fluorescence imaging of in vivo miR-124a-induced neurogenesis of neuronal progenitor cells using neuron-specific reporters

Background

Facilitation of the differentiation of the stem cells toward neuronal lineage is crucial for enhancing the differentiation efficacy of grafted stem cells for the possible treatment of neurodegenerative disorders. MicroRNA124a (miR-124a) has been considered as a neuronal lineage regulator, possessing the capability to activate neuronal differentiation. In this study, using a neuronal promoter-based reporter and live-cell fluorescence imaging, we visualized in vitro and in vivo the enhanced neuronal differentiation of neuronal progenitor cells with miR-124a overproduction.

Methods

The neuron specific alpha1 tubulin promoter-driven RFP reporter (pTa1-RFP) was used to trace the miR-124a-induced neuronal differentiation in live cell condition. MiR-124a or miR-scramble in 10 % glucose buffer was mixed with in vivo-jetPEITM and in vivo fluorescence images were obtained daily using Maestro spectral fluorescent imager.

Results

Neurite outgrowth was clearly seen in F11 cells after miR-124a transfection, and immunofluorescence staining showed increase of Tuj1 and NF at 48 hours. When pTa1-RFP-transfected F11 cells were implanted simultaneously with miR-124a into the nude mice, gradually increasing reporter signals and morphological changes indicated neuronal differentiation for 48 hours in live cells in vitro. The miR-124a-treated F11 cells showed higher reporter signals on in vivo fluorescence imaging than miR-scramble-treated cells, which were verified by ex vivo confirmation of Tuj1 and NF expression.

Conclusions

These results indicated that neuronal reporter-based neurogenesis imaging can be used for monitoring miR-124a acting as neuronal activator when miRNA was injected in in vivo PEI-coated form for miRNA-mediated regenerative therapy.

SIRB, sans iron oxide rhodamine B, a novel cross-linked dextran nanoparticle, labels human neuroprogenitor and SH-SY5Y neuroblastoma cells and serves as a USPIO cell labeling control

This is the first report of the synthesis of a new nanoparticle, sans iron oxide rhodamine B (SIRB), an example of a new class of nanoparticles. SIRB is designed to provide all of the cell labeling properties of the ultrasmall superparamagnetic iron oxide (USPIO) nanoparticle Molday ION Rhodamine B (MIRB) without containing the iron oxide core. MIRB was developed to label cells and allow them to be tracked by MRI or to be manipulated by magnetic gradients. SIRB possesses a similar size, charge and cross-linked dextran coating as MIRB. Of great interest is understanding the biological and physiological changes in cells after they are labeled with a USPIO. Whether these effects are due to the iron oxide buried within the nanoparticle or to the surface coating surrounding the iron oxide core has not been considered previously. MIRB and SIRB represent an ideal pairing of nanoparticles to identify nanoparticle anatomy responsible for post-labeling cytotoxicity. Here we report the effects of SIRB labeling on the SH-SY5Y neuroblastoma cell line and primary human neuroprogenitor cells (hNPCs). These effects are contrasted with the effects of labeling SH-SY5Y cells and hNPCs with MIRB. We find that SIRB labeling, like MIRB labeling, (i) occurs without the use of transfection reagents, (ii) is packaged within lysosomes distributed within cell cytoplasm, (iii) is retained within cells with no loss of label after cell storage, and (iv) does not alter cellular viability or proliferation, and (v) SIRB labeled hNPCs differentiate normally into neurons or astrocytes. Copyright © 2016 John Wiley & Sons, Ltd.

Transcriptional regulatory events initiated by Ascl1 and Neurog2 during neuronal differentiation of P19 embryonic carcinoma cells

As members of the proneural basic-helix-loop-helix (bHLH) family of transcription factors, Ascl1 and Neurog2 direct the differentiation of specific populations of neurons at various times and locations within the developing nervous system. In order to characterize the mechanisms employed by these two bHLH factors, we generated stable, doxycycline-inducible lines of P19 embryonic carcinoma cells that express comparable levels of Ascl1 and Neurog2. Upon induction, both Ascl1 and Neurog2 directed morphological and immunocytochemical changes consistent with initiation of neuronal differentiation. Comparison of Ascl1- and Neurog2-regulated genes by microarray analyses showed both shared and distinct transcriptional changes for each bHLH protein. In both Ascl1- and Neurog2-differentiating cells, repression of Oct4 mRNA levels was accompanied by increased Oct4 promoter methylation. However, DNA demethylation was not detected for genes induced by either bHLH protein. Neurog2-induced genes included glutamatergic marker genes while Ascl1-induced genes included GABAergic marker genes. The Neurog2-specific induction of a gene encoding a protein phosphatase inhibitor, Ppp1r14a, was dependent on distinct, canonical E-box sequences within the Ppp1r14a promoter and the nucleotide sequences within these E-boxes were partially responsible for Neurog2-specific regulation. Our results illustrate multiple novel mechanisms by which Ascl1 and Neurog2 regulate gene repression during neuronal differentiation in P19 cells.

Human neural progenitor cells retain viability, phenotype, proliferation, and lineage differentiation when labeled with a novel iron oxide nanoparticle, Molday ION Rhodamine B

Ultrasmall superparamagnetic iron-oxide particles (USPIOs) loaded into stem cells have been suggested as a way to track stem cell transplantation with magnetic resonance imaging, but the labeling, and post-labeling proliferation, viability, differentiation, and retention of USPIOs within the stem cells have yet to be determined for each type of stem cell and for each type of USPIO. Molday ION Rhodamine B™ (BioPAL, Worcester, MA, USA) (MIRB) has been shown to be a USPIO labeling agent for mesenchymal stem cells, glial progenitor cells, and stem cell lines. In this study, we have evaluated MIRB labeling in human neuroprogenitor cells and found that human neuroprogenitor cells are effectively labeled with MIRB without use of transfection reagents. Viability, proliferation, and differentiation properties are unchanged between MIRB-labeled neuroprogenitors cells and unlabeled cells. Moreover, MIRB-labeled human neuroprogenitor cells can be frozen, thawed, and replated without loss of MIRB or even without loss of their intrinsic biology. Overall, those results show that MIRB has advantageous properties that can be used for cell-based therapy.

Regulation of gene expression during early neuronal differentiation: evidence for patterns conserved across neuron populations and vertebrate classes

Analysis of transcription factor function during neurogenesis has provided a huge amount of data on the generation and specification of diverse neuron populations in the central and peripheral nervous systems of vertebrates. However, an understanding of the induction of key neuron functions including electrical information processing and synaptic transmission lags seriously behind. Whereas pan-neuronal markers such as neurofilaments, neuron-specific tubulin and RNA-binding proteins have often been included in developmental analysis, the molecular players underlying electrical activity and transmitter release have been neglected in studies addressing gene expression during neuronal induction. Here, I summarize the evidence for a distinct accumulation pattern of mRNAs for synaptic proteins, a pattern that is delayed compared with pan-neuronal gene expression during neurogenesis. The conservation of this pattern across diverse avian and mammalian neuron populations suggests a common mechanism for the regulation of various sets of neuronal genes during initial neuronal differentiation. The co-regulation of genes coding for synaptic proteins from embryonic to postnatal development indicates that the expression of the players required for synaptic transmission shares common regulatory features. For the ion channels involved in neuronal electrical activity, such as voltage-gated sodium channels, the situation is less clear because of the lack of comparative studies early during neurogenesis. Transcription factors have been characterized that regulate the expression of synaptic proteins in vitro and in vivo. They currently do not explain the co-regulation of these genes across different neuron populations. The neuron-restrictive silencing factor NRSF/REST targets a large gene set, but not all of the genes coding for pan-neuronal, synaptic and ion channel proteins. The discrepancy between NRSF/REST loss-of-function and silencer-to-activator-switch studies leaves the full functional implications of this factor open. Together with microRNAs, splicing regulators, chromatin remodellers and an increasing list of transcriptional regulators, the factor is embedded in feedback circuits with the potential to orchestrate neuronal differentiation. The precise regulation of the coordinated expression of proteins underlying key neuronal functions by these circuits during neuronal induction is a major emerging topic.