Motoneuronal Sema3C is essential for setting stereotyped motor tract positioning in limb-derived chemotropic semaphorins

Semaphorin 3s signaling in the central nervous system: Mechanisms and therapeutic implication for brain diseases

Class 3 semaphorins (Sema3s), identified as secreted soluble proteins, present many therapeutic potentials. Recent evidence has suggested that Sema3s as molecular cue participate in neuroregulation, angiogenesis, and microenvironment homeostasis of the central nervous system. Moreover, Sema3s signaling pathways may be targeted for enhancing neural network connectivity, promoting neural regeneration and repair, and inhibiting pathological angiogenesis. Due to the complex co-expression patterns and crosstalk among Sema3s, new drugs targeting Sema3s-related signaling pathways are expected to be discovered to counter brain diseases. This review summarizes the specific roles of Sema3s in pathological processes of various brain diseases, and provides potential targeted strategies for the prevention and treatment.

The limb dorsoventral axis: Lmx1b's role in development, pathology, evolution, and regeneration

The limb anatomy displays well-defined dorsal and ventral compartments, housing extensor, and flexor muscles, which play a crucial role in facilitating limb locomotion and manipulation. Despite its importance, the study of limb dorsoventral patterning has been relatively neglected compared to the other two axes leaving many crucial questions about the genes and developmental processes implicated unanswered. This review offers a thorough overview of the current understanding of limb dorsoventral patterning, synthesizing classical literature with recent research. It covers the specification of dorsal fate in the limb mesoderm and its subsequent translation into dorsal morphologies-a process directed by the transcription factor Lmx1b. We also discuss the potential role of dorsoventral patterning in the evolution of paired appendages and delve into the involvement of LMX1B in Nail-Patella syndrome, discussing the molecular and genetic aspects underlying this condition. Finally, the potential role of dorsoventral polarity in digit tip regeneration, a prominent instance of multi-tissue regeneration in mammals is also considered. We anticipate that this review will renew interest in a process that is critical to limb function and evolutionary adaptations but has nonetheless been overlooked.

Motor innervation directs the correct development of the mouse sympathetic nervous system

The sympathetic nervous system controls bodily functions including vascular tone, cardiac rhythm, and the "fight-or-flight response". Sympathetic chain ganglia develop in parallel with preganglionic motor nerves extending from the neural tube, raising the question of whether axon targeting contributes to sympathetic chain formation. Using nerve-selective genetic ablations and lineage tracing in mouse, we reveal that motor nerve-associated Schwann cell precursors (SCPs) contribute sympathetic neurons and satellite glia after the initial seeding of sympathetic ganglia by neural crest. Motor nerve ablation causes mispositioning of SCP-derived sympathoblasts as well as sympathetic chain hypoplasia and fragmentation. Sympathetic neurons in motor-ablated embryos project precociously and abnormally towards dorsal root ganglia, eventually resulting in fusion of sympathetic and sensory ganglia. Cell interaction analysis identifies semaphorins as potential motor nerve-derived signaling molecules regulating sympathoblast positioning and outgrowth. Overall, central innervation functions both as infrastructure and regulatory niche to ensure the integrity of peripheral ganglia morphogenesis.

Motor neurons use push-pull signals to direct vascular remodeling critical for their connectivity

The nervous system requires metabolites and oxygen supplied by the neurovascular network, but this necessitates close apposition of neurons and endothelial cells. We find motor neurons attract vessels with long-range VEGF signaling, but endothelial cells in the axonal pathway are an obstacle for establishing connections with muscles. It is unclear how this paradoxical interference from heterotypic neurovascular contacts is averted. Through a mouse mutagenesis screen, we show that Plexin-D1 receptor is required in endothelial cells for development of neuromuscular connectivity. Motor neurons release Sema3C to elicit short-range repulsion via Plexin-D1, thus displacing endothelial cells that obstruct axon growth. When this signaling pathway is disrupted, epaxial motor neurons are blocked from reaching their muscle targets and concomitantly vascular patterning in the spinal cord is altered. Thus, an integrative system of opposing push-pull cues ensures detrimental axon-endothelial encounters are avoided while enabling vascularization within the nervous system and along peripheral nerves.

Integrated single-cell analyses decode the developmental landscape of the human fetal spine

The spine has essential roles in supporting body weight, and passaging the neural elements between the body and the brain. In this study, we used integrated single-cell RNA sequencing and single-cell transposase-accessible chromatin sequencing analyses to reveal the cellular heterogeneity, lineage, and transcriptional regulatory network of the developing human spine. We found that EPYC + HAPLN1+ fibroblasts with stem cell characteristics could differentiate into chondrocytes by highly expressing the chondrogenic markers SOX9 and MATN4. Neurons could originate from neuroendocrine cells, and MEIS2 may be an essential transcription factor that promotes spinal neural progenitor cells to selectively differentiate into neurons during early gestation. Furthermore, the interaction of NRP2_SEMA3C and CD74_APP between macrophages and neurons may be essential for spinal cord development. Our integrated map provides a blueprint for understanding human spine development in the early and midgestational stages at single-cell resolution and offers a tool for investigating related diseases.

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scRNA-seq and scATAC-seq analyses reveal the developmental landscape of the fetal spine

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Chondrocytes may originate from EPYC + HAPLN1+ fibroblasts with stem cell characteristics

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Neurons may originate from neuroendocrine cells with regulation by MEIS2

Expression of class III Semaphorins and their receptors in the developing chicken (Gallus gallus) inner ear

Class III Semaphorin (Sema) secreted ligands are known to repel neurites expressing Neuropilin (Nrp) and/or Plexin (Plxn) receptors. There is, however, a growing body of literature supporting that Sema signaling also has alternative roles in development such as synaptogenesis, boundary formation, and vasculogenesis. To evaluate these options during inner ear development, we used in situ hybridization or immunohistochemistry to map the expression of Sema3D, Sema3F, Nrp1, Nrp2, and PlxnA1 in the chicken (Gallus gallus) inner ear from embryonic day (E)5-E10. The resulting expression patterns in either the otic epithelium or its surrounding mesenchyme suggest that Sema signaling could be involved in each of the varied functions reported for other tissues. Sema3D expression flanking the sensory tissue in vestibular organs suggests that it may repel Nrp2- and PlxnA1-expressing neurites of the vestibular ganglion away from nonsensory epithelia, thus channeling them into the sensory domains at E5-E8. Expression of Sema signaling genes in the sensory hair cells of both the auditory and vestibular organs on E8-E10 may implicate Sema signaling in synaptogenesis. In the nonsensory regions of the cochlea, Sema3D in the future tegmentum vasculosum opposes Nrp1 and PlxnA1 in the future cuboidal cells; the abutment of ligand and receptors in adjacent domains may enforce or maintain the boundary between them. In the mesenchyme, Nrp1 colocalized with capillary-rich tissue. Sema3D immediately flanks this Nrp1-expressing tissue, suggesting a role in endothelial cell migration towards the inner ear. In summary, Sema signaling may play multiple roles in the developing inner ear.

Semaphorin 3C as a Therapeutic Target in Prostate and Other Cancers

The semaphorins represent a large family of signaling molecules with crucial roles in neuronal and cardiac development. While normal semaphorin function pertains largely to development, their involvement in malignancy is becoming increasingly evident. One member, Semaphorin 3C (SEMA3C), has been shown to drive a number of oncogenic programs, correlate inversely with cancer prognosis, and promote the progression of multiple different cancer types. This report surveys the body of knowledge surrounding SEMA3C as a therapeutic target in cancer. In particular, we summarize SEMA3C's role as an autocrine andromedin in prostate cancer growth and survival and provide an overview of other cancer types that SEMA3C has been implicated in including pancreas, brain, breast, and stomach. We also propose molecular strategies that could potentially be deployed against SEMA3C as anticancer agents such as biologics, small molecules, monoclonal antibodies and antisense oligonucleotides. Finally, we discuss important considerations for the inhibition of SEMA3C as a cancer therapeutic agent.

Birthdate-dependent heterogeneity of oculomotor neurons is involved in transmedian migration in the developing mouse midbrain

During the formation of the oculomotor nucleus (nIII), a subset of cells undergoes transmedian migration, crossing the midline to join the contralateral nucleus. A recent study reported that the onset of transmedian migration of nIII neurons is regulated by Slit/Robo signaling. However, developmental programs that differentiate migratory subpopulations of the nIII remain elusive. Here, we identified cellular and molecular characteristics of nIII neurons that are correlated with their migratory behaviors. Birthdate analysis revealed that contralaterally migrating neurons in the caudal part of the nIII are generated at later stages than uncrossed neurons in the rostral part of the nIII. Furthermore, we found that Slit2 is expressed in the ventral midline of the midbrain and contralaterally migrating neurons. On the other hand, Robo2, a receptor of Sli2, is differentially expressed in subpopulations of rostral and caudal parts of the nIII: uncrossed neurons expressed Robo2 in the developing nIII. These results suggest that spatio-temporal regulation of developmental timings and the molecular signatures of oculomotor neurons are crucial for transmedian migration, which underlies appropriate positioning and stereotyped circuit formation of the nIII in the developing mouse midbrain.

COBLL1 modulates cell morphology and facilitates androgen receptor genomic binding in advanced prostate cancer

Androgen receptor (AR) signaling is essential for prostate cancer progression and acquiring resistance to hormone therapy. However, the molecular pathogenesis through AR activation has not been fully understood. We performed integrative transcriptomic analysis to compare the AR program in a castration-resistant prostate cancer (CRPC) model with that in their parental hormone-sensitive cells. We found that the gene cordon-bleu-like 1 (COBLL1) is highly induced by AR in CRPC model cells. The expression of COBLL1 that possesses an actin-binding domain is up-regulated in clinical prostate cancer tissues and is associated with a poor prognosis for prostate cancer patients. COBLL1 is involved in the cancer cell morphogenesis to a neuron-like cell shape observed in the CRPC model cells, promoting cell growth and migration. Moreover, nuclear COBLL1 interacts with AR to enhance complex formation with CDK1 and facilitates AR phosphorylation for genomic binding in CRPC model cells. Thus, our findings showed the mechanistic relevance of cordon-bleu proteins during the AR-mediated progression to CRPC.

Semaphorin 3C and Its Receptors in Cancer and Cancer Stem-Like Cells

Neurodevelopmental programs are frequently dysregulated in cancer. Semaphorins are a large family of guidance cues that direct neuronal network formation and are also implicated in cancer. Semaphorins have two kinds of receptors, neuropilins and plexins. Besides their role in development, semaphorin signaling may promote or suppress tumors depending on their context. Sema3C is a secreted semaphorin that plays an important role in the maintenance of cancer stem-like cells, promotes migration and invasion, and may facilitate angiogenesis. Therapeutic strategies that inhibit Sema3C signaling may improve cancer control. This review will summarize the current research on the Sema3C pathway and its potential as a therapeutic target.

A gene expression signature predicts recurrence-free survival in meningioma

BACKGROUND

Meningioma is the most common primary brain tumor and has a variable risk of local recurrence. While World Health Organization (WHO) grade generally correlates with recurrence, there is substantial within-grade variation of recurrence risk. Current risk stratification does not accurately predict which patients are likely to benefit from adjuvant radiation therapy (RT). We hypothesized that tumors at risk for recurrence have unique gene expression profiles (GEP) that could better select patients for adjuvant RT.

METHODS

We developed a recurrence predictor by machine learning modeling using a training/validation approach.

RESULTS

Three publicly available AffymetrixU133 gene expression datasets (GSE9438, GSE16581, GSE43290) combining 127 primary, non-treated meningiomas of all grades served as the training set. Unsupervised variable selection was used to identify an 18-gene GEP model (18-GEP) that separated recurrences. This model was validated on 62 primary, non-treated cases with similar grade and clinical variable distribution as the training set. When applied to the validation set, 18-GEP separated recurrences with a misclassification error rate of 0.25 (log-rank p=0.0003). 18-GEP was predictive for tumor recurrence [p=0.0008, HR=4.61, 95%CI=1.89-11.23)] and was predictive after adjustment for WHO grade, mitotic index, sex, tumor location, and Simpson grade [p=0.0311, HR=9.28, 95%CI=(1.22-70.29)]. The expression signature included genes encoding proteins involved in normal embryonic development, cell proliferation, tumor growth and invasion (FGF9, SEMA3C, EDNRA), angiogenesis (angiopoietin-2), cell cycle regulation (CDKN1A), membrane signaling (tetraspanin-7, caveolin-2), WNT-pathway inhibitors (DKK3), complement system (C1QA) and neurotransmitter regulation (SLC1A3, Secretogranin-II).

CONCLUSIONS

18-GEP accurately stratifies patients with meningioma by recurrence risk having the potential to guide the use of adjuvant RT.

Axon pathfinding for locomotion

Motor neurons of the spinal cord are responsible for the assembly of neuromuscular connections indispensable for basic locomotion and skilled movements. A precise spatial relationship exists between the position of motor neuron cell bodies in the spinal cord and the course of their axonal projections to peripheral muscle targets. Motor neuron innervation of the vertebrate limb is a prime example of this topographic organization and by virtue of its accessibility and predictability has provided access to fundamental principles of motor system development and neuronal guidance. The seemingly basic binary map established by genetically defined motor neuron subtypes that target muscles in the limb is directed by a surprisingly large number of directional cues. Rather than being simply redundant, these converging signaling pathways are hierarchically linked and cooperate to increase the fidelity of axon pathfinding decisions. A current priority is to determine how multiple guidance signals are integrated by individual growth cones and how they synergize to delineate class-specific axonal trajectories.

Microenvironment-Driven Shift of Cohesion/Detachment Balance within Tumors Induces a Switch toward Metastasis in Neuroblastoma

Neuroblastoma (NB) is a childhood cancer arising from sympatho-adrenal neural crest cells. Disseminated forms have high frequency of multiple tumoral foci whose etiology remains unknown; NB embryonic origin limits investigations in patients and current models. We developed an avian embryonic model driving human NB tumorigenesis in tissues homologous to patients. We found that aggressive NBs display a metastatic mode, secondary dissemination via peripheral nerves and aorta. Through tumor transcriptional profiling, we found that NB dissemination is induced by the shutdown of a pro-cohesion autocrine signal, SEMA3C, which constrains the tumoral mass. Lowering SEMA3C levels shifts the balance toward detachment, triggering NB cells to collectively evade the tumor. Together with patient cohort analysis, this identifies a microenvironment-driven pro-metastatic switch for NB.

SCO-spondin oligopeptide inhibits angiogenesis in glioblastoma

Angiogenesis plays a critical role in glioblastoma growth and progression. We therefore aimed at evaluating the anti-angiogenic properties of an oligopeptide originating from SCO-spondin (NX) on a model of human glioblastoma. To this end, we studied the impact of NX treatment on human brain endothelial cells (HBMECs) alone or co-cultured with glioblastoma cells (U87-MG) on apoptosis, proliferation, migration and release of angiogenic factors. We further investigated the anti-angiogenic potential of NX on human glioblastoma cells grown on chorio-allantoic membrane (CAM) or in glioblastoma xenografts. The results of our experiments showed that NX treatment impaired the microvascular network and induced a decrease in cell proliferation, vascularization and tumor growth in the CAM model as well as in xenotransplants. Interestingly, our in vitro experiments showed that NX impairs HBMECs migration but also regulates the release of angiogenic factors from U87-MG. These results are confirmed by the profiling of NX-treated U87-MG grown on CAM that highlighted modifications of several genes involved in angiogenesis. In conclusion, NX inhibits tumorigenesis by impairing the ability of glioblastoma cells to induce angiogenesis and by inhibiting endothelial cell migration. This molecule might therefore be an interesting candidate for future cancer therapies.

Expression patterns of Sema3A in developing amniote limbs: With reference to the diversification of peripheral nerve innervation

Paired limbs were acquired in the ancestor of tetrapods and their morphology has been highly diversified in amniotes in relation to the adaptive radiation to the terrestrial environment. These morphological changes may have been induced by modification of the developmental program of the skeletal or muscular system. To complete limb modification, it is also important to change the neuronal framework, because the functions of the limbs rely on neural circuits that involve coordinated movement. Previous studies have shown that class 3 semaphorins (Sema3 semaphorins), which act as repulsive axonal guidance cues, play a crucial role in the formation of the peripheral nerves in mice. Here, we studied the expression pattern of Sema3A orthologues in embryos of developing amniotes, including mouse, chick, soft-shelled turtle, and ocelot gecko. Sema3A transcripts were expressed in restricted mesenchymal parts of the developing limb primordium in all animals studied, and developing spinal nerves appeared to extend through Sema3A-negative regions. These results suggest that a Sema3A-dependent guidance system plays a key role in neuronal circuit formation in amniote limbs. We also found that Sema3A partially overlapped with the distribution of cartilage precursor cells. Based on these results, we propose a model in which axon guidance and skeletogenesis are linked by Sema3A; such mechanisms may underlie functional neuron rearrangement during limb diversification.

Spontaneous cerebrospinal fluid leak from an anomalous thoracic nerve root: case report

The authors report the case of a 28-year-old woman with a spontaneous cerebrospinal fluid leak from the sleeve of a redundant thoracic nerve root. She presented with postural headaches and orthostatic symptoms indicative of intracranial hypotension. CT myelography revealed that the lesion was located at the T-11 nerve root. After failure of conservative management, including blood patches and thrombin glue injections, the patient was successfully treated with surgical decompression and ligation of the duplicate nerve, resulting in full resolution of her orthostatic symptoms.

Bad vessels beware! Semaphorins will sort you out!

Secreted class 3 semaphorins (Sema3), which signal through plexin receptors and mostly use neuropilins (Nrps) as co-receptors, were initially identified for their ability to steer navigating axons in the developing embryo. They were later found to control angiogenesis in physiological and pathological settings as well (Serini et al, 2013). Indeed, the development of a novel and aberrant vasculature is central to the pathogenesis of several human diseases, including cancer and vascular retinopathies (Goel et al, 2011). A large body of evidence demonstrates that in cancer, a massive regression of angiogenesis may trigger hypoxia-driven genetic programs, which in turn can overcome drug inhibitory mechanisms and ultimately favour cancer cell invasion and dissemination. Thus, an emerging concept in molecular medicine is to devise therapeutic strategies that, rather than simply inhibiting angiogenesis, can foster the re-establishment of a structural and functional normal network, a phenomenon often referred to as “vessel normalization” (Goel et al, 2011) (Fig 1). Of note, and in this context, Sema3A (Maione et al, 2009) and Sema3F (Wong et al, 2012) have been reported to favour the normalization of cancer vasculature and impair metastatic dissemination.

α2-chimaerin is required for Eph receptor-class-specific spinal motor axon guidance and coordinate activation of antagonistic muscles

Axonal guidance involves extrinsic molecular cues that bind growth cone receptors and signal to the cytoskeleton through divergent pathways. Some signaling intermediates are deployed downstream of molecularly distinct axon guidance receptor families, but the scope of this overlap is unclear, as is the impact of embryonic axon guidance fidelity on adult nervous system function. Here, we demonstrate that the Rho-GTPase-activating protein α2-chimaerin is specifically required for EphA and not EphB receptor signaling in mouse and chick spinal motor axons. Reflecting this specificity, the loss of α2-chimaerin function disrupts the limb trajectory of extensor-muscle-innervating motor axons the guidance of which depends on EphA signaling. These embryonic defects affect coordinated contraction of antagonistic flexor-extensor muscles in the adult, indicating that accurate embryonic motor axon guidance is critical for optimal neuromuscular function. Together, our observations provide the first functional evidence of an Eph receptor-class-specific intracellular signaling protein that is required for appropriate neuromuscular connectivity.

SYD-1C, UNC-40 (DCC) and SAX-3 (Robo) function interdependently to promote axon guidance by regulating the MIG-2 GTPase

During development, axons must integrate directional information encoded by multiple guidance cues and their receptors. Axon guidance receptors, such as UNC-40 (DCC) and SAX-3 (Robo), can function individually or combinatorially with other guidance receptors to regulate downstream effectors. However, little is known about the molecular mechanisms that mediate combinatorial guidance receptor signaling. Here, we show that UNC-40, SAX-3 and the SYD-1 RhoGAP-like protein function interdependently to regulate the MIG-2 (Rac) GTPase in the HSN axon of C. elegans. We find that SYD-1 mediates an UNC-6 (netrin) independent UNC-40 activity to promote ventral axon guidance. Genetic analysis suggests that SYD-1 function in axon guidance requires both UNC-40 and SAX-3 activity. Moreover, the cytoplasmic domains of UNC-40 and SAX-3 bind to SYD-1 and SYD-1 binds to and negatively regulates the MIG-2 (Rac) GTPase. We also find that the function of SYD-1 in axon guidance is mediated by its phylogenetically conserved C isoform, indicating that the role of SYD-1 in guidance is distinct from its previously described roles in synaptogenesis and axonal specification. Our observations reveal a molecular mechanism that can allow two guidance receptors to function interdependently to regulate a common downstream effector, providing a potential means for the integration of guidance signals.

The nerve growth factor receptor CD271 is crucial to maintain tumorigenicity and stem-like properties of melanoma cells

Background

Large-scale genomic analyses of patient cohorts have revealed extensive heterogeneity between individual tumors, contributing to treatment failure and drug resistance. In malignant melanoma, heterogeneity is thought to arise as a consequence of the differentiation of melanoma-initiating cells that are defined by cell-surface markers like CD271 or CD133.

Results

Here we confirmed that the nerve growth factor receptor (CD271) is a crucial determinant of tumorigenicity, stem-like properties, heterogeneity and plasticity in melanoma cells. Stable shRNA mediated knock-down of CD271 in patient-derived melanoma cells abrogated their tumor-initiating and colony-forming capacity. A genome-wide expression profiling and gene-set enrichment analysis revealed novel connections of CD271 with melanoma-associated genes like CD133 and points to a neural crest stem cell (NCSC) signature lost upon CD271 knock-down. In a meta-analysis we have determined a shared set of 271 differentially regulated genes, linking CD271 to SOX10, a marker that specifies the neural crest. To dissect the connection of CD271 and CD133 we have analyzed 10 patient-derived melanoma-cell strains for cell-surface expression of both markers compared to established cell lines MeWo and A375. We found CD271⁺ cells in the majority of cell strains analyzed as well as in a set of 16 different patient-derived melanoma metastases. Strikingly, only 2/12 cell strains harbored a CD133⁺ sub-set that in addition comprised a fraction of cells of a CD271⁺/CD133⁺ phenotype. Those cells were found in the label-retaining fraction and in vitro deduced from CD271⁺ but not CD271 knock-down cells.

Conclusions

Our present study provides a deeper insight into the regulation of melanoma cell properties and points CD271 out as a regulator of several melanoma-associated genes. Further, our data strongly suggest that CD271 is a crucial determinant of stem-like properties of melanoma cells like colony-formation and tumorigenicity.

Spinal motor neuron migration and the significance of topographic organization in the nervous system

The nervous system displays a high degree of topographic organisation such that neuronal soma position is closely correlated to axonal trajectory. One example of such order is the myotopic organisation of the motor system where spinal motor neuron position parallels that of target muscles. This chapter will discuss the molecular mechanisms underlying motor neuron soma positioning, which include transcriptional control of Reelin signaling and cadherin expression. As the same transcription factors have been shown to control motor axon innervation of target muscles, a simple mechanism of topographic organisation specification is becoming evident raising the question of how coordinating soma position with axon trajectory might be important for nervous system wiring and its function.

Integration of guidance cues: parallel signaling and crosstalk

Growing axons are exposed to various guidance cues en route to their targets. Although many guidance molecules have been identified and their effects on axon behavior extensively studied, how axons react to combinations of signals remains largely unexplored. We review recent studies investigating the combined actions of guidance cues present at the same choice points. Two main scenarios are emerging from these studies: parallel signaling and crosstalk between guidance systems. In the first case, cues act in an additive manner, whereas in the second case the outcome is non-additive and differs from the sum of individual effects, suggesting more complex signal integration in the growth cone. Some of the molecular mechanisms underlying these interactions are beginning to be unraveled.