Sonic hedgehog signaling in the developing CNS where it has been and where it is going

Aberrant FGF signaling promotes granule neuron precursor expansion in SHH subgroup infantile medulloblastoma

Mutations in Sonic Hedgehog (SHH) signaling pathway genes, for example, Suppressor of Fused (SUFU), drive granule neuron precursors (GNP) to form medulloblastomas (MBSHH). However, how different molecular lesions in the Shh pathway drive transformation is frequently unclear, and SUFU mutations in the cerebellum seem distinct. In this study, we show that fibroblast growth factor 5 (FGF5) signaling is integral for many infantile MBSHH cases and that FGF5 expression is uniquely upregulated in infantile MBSHH tumors. Similarly, mice lacking SUFU (Sufu-cKO) ectopically express Fgf5 specifically along the secondary fissure where GNPs harbor preneoplastic lesions and show that FGFR signaling is also ectopically activated in this region. Treatment with an FGFR antagonist rescues the severe GNP hyperplasia and restores cerebellar architecture. Thus, direct inhibition of FGF signaling may be a promising and novel therapeutic candidate for infantile MBSHH.

Linkage between Fuz and Gpr161 genes regulates sonic hedgehog signaling during mouse neural tube development

Sonic hedgehog (Shh) signaling regulates embryonic morphogenesis utilizing the primary cilium, the cell's antenna, which acts as a signaling hub. Fuz, an effector of planar cell polarity signaling, regulates Shh signaling by facilitating cilia formation, and the G protein-coupled receptor 161 (Gpr161) is a negative regulator of Shh signaling. The range of phenotypic malformations observed in mice bearing mutations in either of the genes encoding these proteins is similar; however, their functional relationship has not been previously explored. This study identified the genetic and biochemical linkage between Fuz and Gpr161 in mouse neural tube development. Fuz was found to be genetically epistatic to Gpr161 with respect to regulation of Shh signaling in mouse neural tube development. The Fuz protein biochemically interacts with Gpr161, and Fuz regulates Gpr161-mediated ciliary localization, a process that might utilize β-arrestin 2. Our study characterizes a previously unappreciated Gpr161-Fuz axis that regulates Shh signaling during mouse neural tube development.

The novel linkage between Fuz and Gpr161 genes regulates sonic hedgehog signaling during mouse embryonic development

Sonic hedgehog (Shh) signaling regulates embryonic morphogenesis utilizing primary cilia, the cell antenna acting as a signaling hub. Fuz, an effector of planar cell polarity (PCP) signaling, involves Shh signaling via cilia formation, while the G protein-coupled receptor 161 (Gpr161) is a negative regulator of Shh signaling. The range of phenotypic malformations observed in mice bearing mutations in either of these two genes is similar; however, their functional relations have not been previously explored. This study identified the genetic and biochemical link between Fuz and Gpr161 in mouse embryonic development. Fuz was genetically epistatic to Gpr161 via Shh signaling during mouse embryonic development. The FUZ biochemically interacted with GPR161, and Fuz regulated Gpr161 ciliary trafficking via β-arrestin2. Our study suggested the novel Gpr161-Fuz axis that regulates Shh signaling during mouse embryonic development.

Serum levels of sonic hedgehog in patients with IgA nephropathy are closely associated with intrarenal arteriolar lesions

BACKGROUND

Intrarenal arteriolar disease is a major risk factor for poor prognosis in immunoglobulin A nephropathy (IgAN). The morphologic factor sonic hedgehog (SHH) plays an important role in a variety of vascular diseases, so it may be directly or indirectly involved in the process of renal arteriolar disease. The purpose of this study was to investigate the correlation between serum SHH levels and renal arteriole disease in patients with IgAN.

METHODS

Subjects with primary IgAN diagnosed by renal biopsy performed between October 2018 and August 2019 at the First Medical Center of the Chinese PLA General Hospital were recruited. Blood specimens were collected from the patients within 1 week before renal biopsy after they signed an informed consent form, and healthy controls were recruited for blood specimen collection during the same period. The concentration of serum SHH was measured by enzyme-linked immunosorbent assay in this population.

RESULTS

Serum SHH levels were significantly lower in the IgAN group than in the control group. 41 of the 94 subjects diagnosed with IgAN had severe renal arteriolosclerosis and, compared to their less severely affected counterparts, were older, more hypertensive, and characterized by lower levels of SHH, higher levels of tubular atrophy/interstitial fibrosis and a higher Lee's classification. Serum SHH concentration was found to be an independent predictor of severe intrarenal arteriolosclerosis in IgAN subjects after correction using multivariate analysis.

CONCLUSION

In this study, serum SHH levels were found to be significantly lower in patients with IgAN than in healthy subjects. Serum SHH may serve as a noninvasive biomarker of intrarenal arteriolosclerosis in patients with IgAN.

Targeting the Hedgehog Pathway in Rhabdomyosarcoma

Aberrant activation of the Hedgehog (Hh) signalling pathway is known to play an oncogenic role in a wide range of cancers; in the particular case of rhabdomyosarcoma, this pathway has been demonstrated to be an important player for both oncogenesis and cancer progression. In this review, after a brief description of the pathway and the characteristics of its molecular components, we describe, in detail, the main activation mechanisms that have been found in cancer, including ligand-dependent, ligand-independent and non-canonical activation. In this context, the most studied inhibitors, i.e., SMO inhibitors, have shown encouraging results for the treatment of basal cell carcinoma and medulloblastoma, both tumour types often associated with mutations that lead to the activation of the pathway. Conversely, SMO inhibitors have not fulfilled expectations in tumours-among them sarcomas-mostly associated with ligand-dependent Hh pathway activation. Despite the controversy existing regarding the results obtained with SMO inhibitors in these types of tumours, several compounds have been (or are currently being) evaluated in sarcoma patients. Finally, we discuss some of the reasons that could explain why, in some cases, encouraging preclinical data turned into disappointing results in the clinical setting.

Pax6 limits the competence of developing cerebral cortical cells to respond to inductive intercellular signals

The development of stable specialized cell types in multicellular organisms relies on mechanisms controlling inductive intercellular signals and the competence of cells to respond to such signals. In developing cerebral cortex, progenitors generate only glutamatergic excitatory neurons despite being exposed to signals with the potential to initiate the production of other neuronal types, suggesting that their competence is limited. Here, we tested the hypothesis that this limitation is due to their expression of transcription factor Pax6. We used bulk and single-cell RNAseq to show that conditional cortex-specific Pax6 deletion from the onset of cortical neurogenesis allowed some progenitors to generate abnormal lineages resembling those normally found outside the cortex. Analysis of selected gene expression showed that the changes occurred in specific spatiotemporal patterns. We then compared the responses of control and Pax6-deleted cortical cells to in vivo and in vitro manipulations of extracellular signals. We found that Pax6 loss increased cortical progenitors' competence to generate inappropriate lineages in response to extracellular factors normally present in developing cortex, including the morphogens Shh and Bmp4. Regional variation in the levels of these factors could explain spatiotemporal patterns of fate change following Pax6 deletion in vivo. We propose that Pax6's main role in developing cortical cells is to minimize the risk of their development being derailed by the potential side effects of morphogens engaged contemporaneously in other essential functions.

Exploring Sonic Hedgehog Cell Signaling in Neurogenesis: Its Potential Role in Depressive Behavior

Depression is the most prevalent form of neuropsychiatric disorder affecting all age groups globally. As per the estimation of the World Health Organization (WHO), depression will develop into the foremost reason for disability globally by the year 2030. The primary neurobiological mechanism implicated in depression remains ambiguous; however, dysregulation of molecular and signaling transductions results in depressive disorders. Several theories have been developed to explain the pathogenesis of depression, however, none of them completely explained all aspects of depressive-pathogenesis. In the current review, we aimed to explore the role of the sonic hedgehog (Shh) signaling pathway in the development of the depressive disorder and its potential as the therapeutic target. Shh signaling has a crucial function in neurogenesis and neural tube patterning during the development of the central nervous system (CNS). Shh signaling performs a basic function in embryogenesis and hippocampal neurogenesis. Moreover, antidepressants are also known to enhance neurogenesis in the hippocampus, which further suggests the potential of Shh signaling. Furthermore, there is decreased expression of a glioma-associated oncogene (Gli1) and Smoothened (Smo) in depression. Moreover, antidepressants also regulate brain-derived neurotrophic factor (BDNF) and wingless protein (Wnt) signaling, therefore, Shh may be implicated in the pathogenesis of the depressive disorder. Deregulation of Shh signaling in CNS results in neurological disorders such as depression.

A Shh/Gli-driven three-node timer motif controls temporal identity and fate of neural stem cells

How time is measured by neural stem cells during temporal neurogenesis has remained unresolved. By combining experiments and computational modeling, we define a Shh/Gli-driven three-node timer underlying the sequential generation of motor neurons (MNs) and serotonergic neurons in the brainstem. The timer is founded on temporal decline of Gli-activator and Gli-repressor activities established through down-regulation of Gli transcription. The circuitry conforms an incoherent feed-forward loop, whereby Gli proteins not only promote expression of Phox2b and thereby MN-fate but also account for a delayed activation of a self-promoting transforming growth factor-β (Tgfβ) node triggering a fate switch by repressing Phox2b. Hysteresis and spatial averaging by diffusion of Tgfβ counteract noise and increase temporal accuracy at the population level, providing a functional rationale for the intrinsically programmed activation of extrinsic switch signals in temporal patterning. Our study defines how time is reliably encoded during the sequential specification of neurons.

A selective D2 dopamine receptor agonist alleviates depression through up-regulation of tyrosine hydroxylase and increased neurogenesis in hippocampus of the prenatally stressed rats

Prenatal stress (PNS) has its negative impact on both the infant hippocampal neurogenesis and pregnancy outcomes in the neonates that serves as a risk factor for postnatal depression in adult offsprings. Therefore, main objectives of the present study were to evaluate the effect of maternal chronic unpredictable mild stress (CUMS) on behavioural changes, levels of oxidative stress, changes in selective developmental signaling genes and neurogenesis in the adult brain of Wistar rats and its reversal through a selective non-ergoline D2 type dopamine receptor (D2R) agonist Ropinirole (ROPI). Effects of ROPI treatment on CUMS induced adult rats offspring were measured by assessment of behavioural tests (sucrose preference test and forced swim test), biomarkers of oxidative stress, protein expression of tyrosine hydroxylase (TH), mRNA expression of SHH, GSK-3β, β-catenin, Notch, brain-derived neurotrophic factor (BDNF), Dopamine receptor 2 (Drd2) and bromodeoxyuridine (BrdU) cell proliferation assay. The oxidative stress, protein and mRNA expression were determined in the hippocampus and prefrontal cortex while the BrdU cell proliferation was observed in the hippocampus of rat brain. PNS induced changes resulted in depression validated by the depression-like behaviours, increased oxidative stress, decreased TH expression, altered expression of selective developmental genes, along with the reduced hippocampal neurogenesis and BDNF expression in the brain of adult offsprings. Chronic ROPI treatment reversed those effects and was equally effective like Imipramine (IMI) treatment. So, the present study suggested that ROPI can be used as an antidepressant drug for the treatment of depressive disorders.

State of the art of Smo antagonists for cancer therapy: advances in the target receptor and new ligand structures

Since the Hedgehog signaling pathway has been associated with cancer, it has emerged as a therapeutic target for cancer therapy. The main target among the key Hedgehog proteins is the GPCR-like Smo receptor. Therefore, some Smo antagonists that have entered clinical trials, including the US FDA-approved drugs vismodegib and sonidegib, to treat basal cell carcinoma and medulloblastoma. However, early resistance of these drugs has spawned the need to understand the molecular bases of this phenomena. We therefore reviewed details about Smo receptor structures and the best Smo antagonist chemical structures. In addition, we discussed strategies that should be considered to develop new, safer generations of Smo antagonists that avoid current clinical limitations.

Effects of chronic unpredictable mild stress induced prenatal stress on neurodevelopment of neonates: Role of GSK-3β

Prenatal stress (PNS) has gained attention with regard to its impact on hippocampal neurogenesis in neonates which serves as a risk factor for postnatal neurodevelopmental deficits. Evidences from animal models have suggested that depression responsive hypothalamic-pituitary-adrenal (HPA) axis and its hormonal response via cortisol, is responsible for critical neurodevelopmental deficits in the offspring which is transduced due to gestational stress. But knowledge in the area of assessing the effects of maternal chronic unpredictable mild stress (CUMS) on neurogenesis and expression of some key signaling molecules in the offsprings are limited. We have used Wistar rats to induce PNS in offsprings by maternal CUMS during pregnancy. Prefrontal cortex (PFC) and hippocampus were assessed for biomarkers of oxidative stress, neurogenesis, neurodevelopmental signaling molecules and DNA damage in the male Wister offsprings. Our investigations resulted in sufficient evidences which prove how maternal psychological stress has widespread effect on the fetal outcomes via major physiological alteration in the antioxidant levels, neurogenesis, signaling molecules and DNA damage. PNS leads to the upregulation of GSK-3β which in turn inhibited mRNA and protein expressions of sonic hedgehog (SHH), β-catenin, Notch and brain derived neurotrophic factor (BDNF). The study explored multifaceted signaling molecules especially, GSK-3β responsible for crosstalks between different neurodevelopmental molecules like SHH, Notch, BDNF and β-catenin affecting neurodevelopment of the offsprings due to PNS.

Direct transdifferentiation of human Wharton's jelly mesenchymal stromal cells into cholinergic-like neurons

Barckground Alzheimer's disease (AD) is mainly caused by cellular loss and dysfunction of the basal forebrain cholinergic neurons and cholinergic axons in the cortex leading to slowly progressive decline in learning and memory performance. Unfortunately, no definitive treatment to halt neural cell loss exists to date. Therefore, it is necessary to obtain an unlimited source of cholinergic neurons for future pharmacological applications in AD. Human mesenchymal stromal cells (hMSCs) represent a unique source of cholinergic-like neurons (ChLNs). New method hWJ-MSCs were incubated with Cholinergic-N-Run medium for 4 and 7 days. Results hWJ-MSCs cultured with Cholinergic-N-Run medium differentiated into ChLNs in 4 days as evidenced by high levels of protein expression of the neuronal markers ChAT, VAChT, AChE, MAP2, β-Tubulin III, NeuN, TUC-4, NF-L and no expression of the immature marker SOX2, the dopaminergic marker TH, GABAergic marker GAD67 and glial marker GFAP. Comparison with existing method(s) The hWJ-MSCs form ChLNs (e.g., ∼26% IF+) within 20 days by using complex conditioned mediums that are expensive and time-consuming. We report for the first time, to our best knowledge, a direct method of hWJ-MSCs transdifferentiation into ChLNs (∼76% ChAT /VAChT assessed by immunofluorescence microscopy and flow cytometry) in an economic, efficient and timely fashion. Conclusions The fastest method to obtain ChLNs from hWJ-MSCs takes only four days using the one-step incubation medium Cholinergic-N-Run.

Bid Expression Network Controls Neuronal Cell Fate During Avian Ciliary Ganglion Development

Avian ciliary ganglion (CG) development involves a transient execution phase of apoptosis controlling the final number of neurons, but the time-dependent molecular mechanisms for neuronal cell fate are largely unknown. To elucidate the molecular networks regulating important aspects of parasympathetic neuronal development, a genome-wide expression analysis was performed during multiple stages of avian CG development between embryonic days E6 and E14. The transcriptome data showed a well-defined sequence of events, starting from neuronal migration via neuronal fate cell determination, synaptic transmission, and regulation of synaptic plasticity to growth factor associated signaling. In particular, we extracted a neuronal apoptosis network that characterized the cell death execution phase at E8/E9 and apoptotic cell clearance at E14 by combining the gene time series analysis with network synthesis from the chicken interactome. Network analysis identified TP53 as key regulator and predicted involvement of the BH3 interacting domain death agonist (BID). A virus-based RNAi knockdown approach in vivo showed a crucial impact of BID expression on the execution of ontogenetic programmed cell death (PCD). In contrast, Bcl-XL expression did not impact PCD. Therefore, BID-mediated apoptosis represents a novel cue essential for timing within CG maturation.

Sonic Hedgehog Signaling and Hippocampal Neuroplasticity

Sonic hedgehog (Shh) is a secreted protein that controls the patterning of neural progenitor cells, and their neuronal and glial progeny, during development. Emerging findings suggest that Shh also has important roles in the formation and plasticity of neuronal circuits in the hippocampus, a brain region of fundamental importance in learning and memory. Shh mediates activity-dependent and injury-induced hippocampal neurogenesis. Activation of Shh receptors in the dendrites of hippocampal neurons engages a trans-neuronal signaling pathway that accelerates axon outgrowth and enhances glutamate release from presynaptic terminals. Impaired Shh signaling may contribute to the pathogenesis of several developmental and adult-onset neurological disorders that affect the hippocampus, suggesting a potential for therapeutic interventions that target Shh pathways.

Tcf7l2/Tcf4 Transcriptional Repressor Function Requires HDAC Activity in the Developing Vertebrate CNS

The generation of functionally distinct neuronal subtypes within the vertebrate central nervous system (CNS) requires the precise regulation of progenitor gene expression in specific neuronal territories during early embryogenesis. Accumulating evidence has implicated histone deacetylase (HDAC) proteins in cell specification, proliferation, and differentiation in diverse embryonic and adult tissues. However, although HDAC proteins have shown to be expressed in the developing vertebrate neural tube, their specific role in CNS neural progenitor fate specification remains unclear. Prior work from our lab showed that the Tcf7l2/Tcf4 transcription factor plays a key role in ventral progenitor lineage segregation by differential repression of two key specification factors, Nkx2.2 and Olig2. In this study, we found that administration of HDAC inhibitors (Valproic Acid (VPA), Trichostatin-A (TSA), or sodium butyrate) in chick embryos in ovo disrupted normal progenitor gene segregation in the developing neural tube, indicating that HDAC activity is required for this process. Further, using functional and pharmacological approaches in vivo, we found that HDAC activity is required for the differential repression of Nkx2.2 and Olig2 by Tcf7l2/Tcf4. Finally, using dominant-negative functional assays, we provide evidence that Tcf7l2/Tcf4 repression also requires Gro/TLE/Grg co-repressor factors. Together, our data support a model where the transcriptional repressor activity of Tcf7l2/Tcf4 involves functional interactions with both HDAC and Gro/TLE/Grg co-factors at specific target gene regulatory elements in the developing neural tube, and that this activity is required for the proper segregation of the Nkx2.2 (p3) and Olig2 (pMN) expressing cells from a common progenitor pool.

Suppressor of Fused Is Critical for Maintenance of Neuronal Progenitor Identity during Corticogenesis

Proper lineage progression and diversification of neural progenitor cells (NPCs) ensures the generation of projection neuron (PN) subtypes in the mammalian neocortex. Here, we show that Suppressor of Fused (Sufu) controls PN specification by maintaining the identity of NPCs in the embryonic neocortex. Deletion of Sufu in NPCs of the E10.5 mouse neocortex led to improper specification of progenitors and a reduction in intermediate progenitors (IPs) during corticogenesis. We found that Sufu deletion resulted in unstable Gli2 and Gli3 activity, leading to the ectopic activation of Sonic hedgehog (Shh) signaling. The role of Sufu in maintaining progenitor identity is critical at early stages of corticogenesis, since deletion of Sufu at E13.5 did not cause similar abnormalities. Our studies revealed that Sufu critically modulates Shh signaling at early stages of neurogenesis for proper specification and maintenance of cortical NPCs to ensure the appropriate generation of cortical PN lineages.

Chronic up-regulation of the SHH pathway normalizes some developmental effects of trisomy in Ts65Dn mice

Down Syndrome (DS) is a highly complex developmental genetic disorder caused by trisomy for human chromosome 21 (Hsa21). All individuals with DS exhibit some degree of brain structural changes and cognitive impairment; mouse models such as Ts65Dn have been instrumental in understanding the underlying mechanisms. Several phenotypes of DS might arise from a reduced response of trisomic cells to the Sonic Hedgehog (SHH) growth factor. If all trisomic cells show a similar reduced response to SHH, then up-regulation of the pathway in trisomic cells might ameliorate multiple DS phenotypes. We crossed Ptch1tm1Mps/+ mice, in which the canonical SHH pathway is expected to be up-regulated in every SHH-responsive cell due to the loss of function of one allele of the pathway suppressor, Ptch1, to the Ts65Dn DS model and assessed the progeny for possible rescue of multiple DS-related phenotypes. Down-regulation of Ptch produced several previously unreported effects on development by itself, complicating interpretation of some phenotypes, and a number of structural or behavioral effects of trisomy were not compensated by SHH signaling. However, a deficit in a nest-building task was partially restored in Ts;Ptch+/- mice, as were the structural anomalies of the cerebellum seen in Ts65Dn mice. These results extend the body of evidence indicating that reduced response to SHH in trisomic cells and tissues contributes to various aspects of the trisomic phenotype.

Primary cilia in neurodevelopmental disorders

Primary cilia are generally solitary organelles that emanate from the surface of almost all vertebrate cell types. Until recently, details regarding the function of these structures were lacking; however, extensive evidence now suggests that primary cilia have critical roles in sensing the extracellular environment, and in coordinating developmental and homeostatic signalling pathways. Furthermore, disruption of these functions seems to underlie a diverse spectrum of disorders, known as primary ciliopathies. These disorders are characterized by wide-ranging clinical and genetic heterogeneity, but with substantial overlap among distinct conditions. Indeed, ciliopathies are associated with a large variety of manifestations that often include distinctive neurological findings. Herein, we review neurological features associated with primary ciliopathies, highlight genotype-phenotype correlations, and discuss potential mechanisms underlying these findings.

Asymmetric activation of Dll4-Notch signaling by Foxn4 and proneural factors activates BMP/TGFβ signaling to specify V2b interneurons in the spinal cord

During development of the ventral spinal cord, the V2 interneurons emerge from p2 progenitors and diversify into two major subtypes, V2a and V2b, that play key roles in locomotor coordination. Dll4-mediated Notch activation in a subset of p2 precursors constitutes the crucial first step towards generating neuronal diversity in this domain. The mechanism behind the asymmetric Notch activation and downstream signaling events are, however, unknown at present. We show here that the Ascl1 and Neurog basic helix-loop-helix (bHLH) proneural factors are expressed in a mosaic pattern in p2 progenitors and that Foxn4 is required for setting and maintaining this expression mosaic. By binding directly to a conserved Dll4 enhancer, Foxn4 and Ascl1 activate Dll4 expression, whereas Neurog proteins prevent this effect, thereby resulting in asymmetric activation of Dll4 expression in V2 precursors expressing different combinations of proneural and Foxn4 transcription factors. Lineage tracing using the Cre-LoxP system reveals selective expression of Dll4 in V2a precursors, whereas Dll4 expression is initially excluded from V2b precursors. We provide evidence that BMP/TGFβ signaling is activated in V2b precursors and that Dll4-mediated Notch signaling is responsible for this activation. Using a gain-of-function approach and by inhibiting BMP/TGFβ signal transduction with pathway antagonists and RNAi knockdown, we further demonstrate that BMP/TGFβ signaling is both necessary and sufficient for V2b fate specification. Our data together thus suggest that the mosaic expression of Foxn4 and proneural factors may serve as the trigger to initiate asymmetric Dll4-Notch and subsequent BMP/TGFβ signaling events required for neuronal diversity in the V2 domain.

The hedgehog pathway gene shifted functions together with the hmgcr-dependent isoprenoid biosynthetic pathway to orchestrate germ cell migration

The Drosophila embryonic gonad is assembled from two distinct cell types, the Primordial Germ Cells (PGCs) and the Somatic Gonadal Precursor cells (SGPs). The PGCs form at the posterior of blastoderm stage embryos and are subsequently carried inside the embryo during gastrulation. To reach the SGPs, the PGCs must traverse the midgut wall and then migrate through the mesoderm. A combination of local repulsive cues and attractive signals emanating from the SGPs guide migration. We have investigated the role of the hedgehog (hh) pathway gene shifted (shf) in directing PGC migration. shf encodes a secreted protein that facilitates the long distance transmission of Hh through the proteoglycan matrix after it is released from basolateral membranes of Hh expressing cells in the wing imaginal disc. shf is expressed in the gonadal mesoderm, and loss- and gain-of-function experiments demonstrate that it is required for PGC migration. Previous studies have established that the hmgcr-dependent isoprenoid biosynthetic pathway plays a pivotal role in generating the PGC attractant both by the SGPs and by other tissues when hmgcr is ectopically expressed. We show that production of this PGC attractant depends upon shf as well as a second hh pathway gene gγ1. Further linking the PGC attractant to Hh, we present evidence indicating that ectopic expression of hmgcr in the nervous system promotes the release/transmission of the Hh ligand from these cells into and through the underlying mesodermal cell layer, where Hh can contact migrating PGCs. Finally, potentiation of Hh by hmgcr appears to depend upon cholesterol modification.

The molecular mechanisms underlying directed cell migration have been studied extensively in different biological contexts. Germ cell migration provides an effective model to study the dynamics of in vivo cell migration. The process of germ cell migration in Drosophila melanogaster results in embryonic gonad formation consisting of primordial germ cells (PGCs) and somatic gonadal precursor cells (SGPs). Moreover, it likely involves a complex series of attractive and repulsive cues. Molecular and genetic analysis has been performed to elucidate the nature of the attractive cue(s) and components that guide germ cells to the SGPs in the mesoderm. One current model proposes that 3-Hydroxy-3-Methylglutaryl Coenzyme A reductase (Hmgcr), synthesized in the SGPs, potentiates signaling downstream of Hedgehog (Hh) ligand also emanating from the SGPs. The model pivots on the novel activity of an established morphogen, Hedgehog, to function as a chemoattractant for the migrating germ cells. A variety of ‘loss-’ and ‘gain-of-function’ strategies manipulating different components of this signaling pathway have been successfully employed in support of the proposed model.

Floor plate-derived sonic hedgehog regulates glial and ependymal cell fates in the developing spinal cord

Cell fate specification in the CNS is controlled by the secreted morphogen sonic hedgehog (Shh). At spinal cord levels, Shh produced by both the notochord and floor plate (FP) diffuses dorsally to organize patterned gene expression in dividing neural and glial progenitors. Despite the fact that two discrete sources of Shh are involved in this process, the individual contribution of the FP, the only intrinsic source of Shh throughout both neurogenesis and gliogenesis, has not been clearly defined. Here, we have used conditional mutagenesis approaches in mice to selectively inactivate Shh in the FP (Shh(FP)) while allowing expression to persist in the notochord, which underlies the neural tube during neurogenesis but not gliogenesis. We also inactivated Smo, the common Hh receptor, in neural tube progenitors. Our findings confirm and extend prior studies suggesting an important requirement for Shh(FP) in specifying oligodendrocyte cell fates via repression of Gli3 in progenitors. Our studies also uncover a connection between embryonic Shh signaling and astrocyte-mediated reactive gliosis in adults, raising the possibility that this pathway is involved in the development of the most common cell type in the CNS. Finally, we find that intrinsic spinal cord Shh signaling is required for the proper formation of the ependymal zone, the epithelial cell lining of the central canal that is also an adult stem cell niche. Together, our studies identify a crucial late embryonic role for Shh(FP) in regulating the specification and differentiation of glial and epithelial cells in the mouse spinal cord.

Structure-function studies with G protein-coupled receptors as a paradigm for improving drug discovery and development of therapeutics

There are a great variety of human membrane proteins, and these currently form the largest group of targets for marketed drugs. Despite the advances in drug design, however, promiscuity between drug molecules and targets often leads to undesired signaling effects, which result in unintended side effects. In this review, one family of membrane proteins - the G protein-coupled receptors (GPCRs) - is used as a model to review experimental techniques that may be used to examine the activity of membrane proteins. As these receptors are highly relevant to healthy human physiology and represent the largest family of drug targets, they represent an excellent model for membrane proteins in general. We also review experimental evidence that suggests there may be multiple ways to target a GPCR - and by extension, membrane proteins - to more effectively target unhealthy phenotypes while reducing the occurrence and severity of side effects.

NVP-LDE-225 (Erismodegib) inhibits epithelial-mesenchymal transition and human prostate cancer stem cell growth in NOD/SCID IL2Rγ null mice by regulating Bmi-1 and microRNA-128

Prostate cancer stem cells (CSCs) are defined by their extensive self-renewal, differentiation and tumor initiation properties. It is now clear that CSCs are involved in tumor growth and recurrence, and resistance to conventional treatments. The sonic hedgehog (Shh) pathway has a crucial role in stemness and tumorigenesis. Thus, the strategy that suppresses stemness and consequently tumorigenic potential of CSCs could be considered for the management of prostate cancer. The objectives of this study were to examine the molecular mechanisms, by which NVP-LDE-225/Erismodegib (smoothened inhibitor) regulates stem cell characteristics and tumor growth in prostate cancer. The effects of NVP-LDE-225 on CSC's viability, sphere formation, apoptosis, epithelial-mesenchymal transition (EMT) and tumor growth in NOD/SCID IL2Rγ null mice were examined. NVP-LDE-225 inhibited cell viability and spheroid formation, and induced apoptosis by activation of caspase-3 and cleavage of poly-ADP ribose polymerase (PARP). NVP-LDE-225 induced expression of Bax and Bak, and inhibited the expression of Bcl-2, Bcl-XL, XIAP, cIAP1, cIAP2 and survivin. NVP-LDE-225 inhibited Gli transcriptional activity, Gli-DNA interaction and the expression of Gli1, Gli2, Patched1 and Patched-2 in prostate CSCs. Interestingly, NVP-LDE-225 induced PDCD4 and apoptosis and inhibited cell viability by suppressing miR-21. Furthermore, NVP-LDE-225 inhibited pluripotency-maintaining factors Nanog, Oct-4, c-Myc and Sox-2. The inhibition of Bmi-1 by NVP-LDE-225 was regulated by upregulation of miR-128. NVP-LDE-225 suppressed EMT by upregulating E-cadherin and inhibiting N-cadherin, Snail, Slug and Zeb1 by regulating the miR-200 family. Finally, NVP-LDE-225 inhibited CSC tumor growth, which was associated with the suppression of Gli1, Gli2, Patched-1, Patched-2, Cyclin D1, Bmi-1 and PCNA and cleavage of caspase-3 and PARP in tumor tissues derived from NOD/SCID IL2Rγ null mice. Overall, our findings suggest that inhibition of the Shh signaling pathway could therefore be a novel therapeutic option in treating prostate cancer.

NPV-LDE-225 (Erismodegib) inhibits epithelial mesenchymal transition and self-renewal of glioblastoma initiating cells by regulating miR-21, miR-128, and miR-200

BACKGROUND

Glioblastoma multiforme is the most common form of primary brain tumor, often characterized by poor survival. Glioblastoma initiating cells (GICs) regulate self-renewal, differentiation, and tumor initiation properties and are involved in tumor growth, recurrence, and resistance to conventional treatments. The sonic hedgehog (SHH) signaling pathway is essential for normal development and embryonic morphogenesis. The objectives of this study were to examine the molecular mechanisms by which GIC characteristics are regulated by NPV-LDE-225 (Smoothened inhibitor; (2,2'-[[dihydro-2-(4-pyridinyl)-1,3(2H,4H)-pyrimidinediyl]bis(methylene)]bis[N,N-dimethylbenzenamine).

METHODS

Cell viability and apoptosis were measured by XTT and annexin V-propidium iodide assay, respectively. Gli translocation and transcriptional activities were measured by immunofluorescence and luciferase assay, respectively. Gene and protein expressions were measured by quantitative real-time PCR and Western blot analyses, respectively.

RESULTS AND CONCLUSION

NPV-LDE-225 inhibited cell viability, neurosphere formation, and Gli transcriptional activity and induced apoptosis by activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase. NPV-LDE-225 increased the expression of tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-R1/DR4, TRAIL-R2/DR5, and Fas and decreased the expression of platelet derived growth factor receptor-α and Bcl2, and these effects were abrogated by Gli1 plus Gli2 short hairpin RNAs. NPV-LDE-225 enhanced the therapeutic potential of FasL and TRAIL by upregulating Fas and DR4/5, respectively. Interestingly, NPV-LDE-225 induced expression of programmed cell death 4 and apoptosis and inhibited cell viability by suppressing micro RNA (miR)-21. Furthermore, NPV-LDE-225 inhibited pluripotency-maintaining factors Nanog, Oct4, Sox2, and cMyc. The inhibition of Bmi1 by NPV-LDE-225 was regulated by induction of miR-128. Finally, NPV-LDE-225 suppressed epithelial-mesenchymal transition by upregulating E-cadherin and inhibiting N-cadherin, Snail, Slug, and Zeb1 through modulating the miR-200 family. Our data highlight the importance of the SHH pathway for self-renewal and early metastasis of GICs.

Astrocyte-derived sonic hedgehog contributes to angiogenesis in brain microvascular endothelial cells via RhoA/ROCK pathway after oxygen-glucose deprivation

The human adult brain possesses intriguing plasticity, including neurogenesis and angiogenesis, which may be mediated by the activated sonic hedgehog (Shh). By employing a coculture system, brain microvascular endothelial cells (BMECs) cocultured with astrocytes, which were incubated under oxygen-glucose deprivation (OGD) condition, we tested the hypothesis that Shh secreted by OGD-activated astrocytes promotes cerebral angiogenesis following ischemia. The results of this study demonstrated that Shh was mainly secreted by astrocytes and the secretion was significantly upregulated after OGD. The proliferation, migration, and tube formation of BMECs cocultured with astrocytes after OGD were significantly enhanced, but cyclopamine (a Shh antagonist) or 5E1 (an antibody of Shh) reversed the change. Furthermore, silencing Ras homolog gene family, member A (RhoA) of BMECs by RNAi and blocking Rho-dependent kinase (ROCK) by Y27632, a specific antagonist of ROCK, suppressed the upregulation of proliferation, migration, and tube formation of BMECs after OGD. These findings suggested that Shh derived from activated astrocytes stimulated RhoA/ROCK pathway in BMECs after OGD, which might be involved in angiogenesis in vitro.

Regulation of thalamic development by sonic hedgehog

The thalamus is strategically positioned within the caudal diencephalic area of the forebrain, between the mesencephalon and telencephalon. This location is important for unique aspects of thalamic function, to process and relay sensory and motor information to and from the cerebral cortex. How the thalamus comes to reside within this region of the central nervous system has been the subject of much investigation. Extracellular signals secreted from key locations both extrinsic and intrinsic to the thalamic primordium have recently been identified and shown to play important roles in the growth, regionalization, and specification of thalamic progenitors. One factor in particular, the secreted morphogen Sonic hedgehog (Shh), has been implicated in spatiotemporal and threshold models of thalamic development that differ from other areas of the CNS due, in large part, to its expression within two signaling centers, the basal plate and the zona limitans intrathalamica, a dorsally projecting spike that separates the thalamus from the subthalamic region. Shh signaling from these dual sources exhibit unique and overlapping functions in the control of thalamic progenitor identity and nuclei specification. This review will highlight recent advances in our understanding of Shh function during thalamic development, revealing similarities, and differences that exist between species.