Developmental biology of the meninges

Unraveling the Complexity of Human Brain: Structure, Function in Healthy and Disease States

The human brain stands as an intricate organ, embodying a nexus of structure, function, development, and diversity. This review delves into the multifaceted landscape of the brain, spanning its anatomical intricacies, diverse functional capacities, dynamic developmental trajectories, and inherent variability across individuals. The dynamic process of brain development, from early embryonic stages to adulthood, highlights the nuanced changes that occur throughout the lifespan. The brain, a remarkably complex organ, is composed of various anatomical regions, each contributing uniquely to its overall functionality. Through an exploration of neuroanatomy, neurophysiology, and electrophysiology, this review elucidates how different brain structures interact to support a wide array of cognitive processes, sensory perception, motor control, and emotional regulation. Moreover, it addresses the impact of age, sex, and ethnic background on brain structure and function, and gender differences profoundly influence the onset, progression, and manifestation of brain disorders shaped by genetic, hormonal, environmental, and social factors. Delving into the complexities of the human brain, it investigates how variations in anatomical configuration correspond to diverse functional capacities across individuals. Furthermore, it examines the impact of neurodegenerative diseases on the structural and functional integrity of the brain. Specifically, our article explores the pathological processes underlying neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases, shedding light on the structural alterations and functional impairments that accompany these conditions. We will also explore the current research trends in neurodegenerative diseases and identify the existing gaps in the literature. Overall, this article deepens our understanding of the fundamental principles governing brain structure and function and paves the way for a deeper understanding of individual differences and tailored approaches in neuroscience and clinical practice-additionally, a comprehensive understanding of structural and functional changes that manifest in neurodegenerative diseases.

From neural tube to spinal cord: The dynamic journey of the dorsal neuroepithelium

In a developing embryo, formation of tissues and organs is remarkably precise in both time and space. Through cell-cell interactions, neighboring progenitors coordinate their activities, sequentially generating distinct types of cells. At present, we only have limited knowledge, rather than a systematic understanding, of the underlying logic and mechanisms responsible for cell fate transitions. The formation of the dorsal aspect of the spinal cord is an outstanding model to tackle these dynamics, as it first generates the peripheral nervous system and is later responsible for transmitting sensory information from the periphery to the brain and for coordinating local reflexes. This is reflected first by the ontogeny of neural crest cells, progenitors of the peripheral nervous system, followed by formation of the definitive roof plate of the central nervous system and specification of adjacent interneurons, then a transformation of roof plate into dorsal radial glia and ependyma lining the forming central canal. How do these peripheral and central neural branches segregate from common progenitors? How are dorsal radial glia established concomitant with transformation of the neural tube lumen into a central canal? How do the dorsal radial glia influence neighboring cells? This is only a partial list of questions whose clarification requires the implementation of experimental paradigms in which precise control of timing is crucial. Here, we outline some available answers and still open issues, while highlighting the contributions of avian models and their potential to address mechanisms of neural patterning and function.

The path to leptomeningeal metastasis

The leptomeninges, the cerebrospinal-fluid-filled tissues surrounding the central nervous system, play host to various pathologies including infection, neuroinflammation and malignancy. Spread of systemic cancer into this space, termed leptomeningeal metastasis, occurs in 5-10% of patients with solid tumours and portends a bleak clinical prognosis. Previous, predominantly descriptive, clinical studies have provided few insights. Recent development of preclinical leptomeningeal metastasis models, alongside genomic, transcriptomic and proteomic sequencing efforts, has provided groundwork for mechanistic understanding and identification of long-needed therapeutic targets. Although previously understood as an anatomically isolated compartment, the leptomeninges are increasingly appreciated as a major conduit of communication between the systemic circulation and the central nervous system. Despite the unique nature of the leptomeningeal microenvironment, the general principles of metastasis hold true: cells metastasizing to the leptomeninges must gain access to the new environment, survive within the space and evade the immune system. The study of leptomeningeal metastasis has the potential to uncover novel site-specific metastatic principles and illuminate the physiology of the leptomeningeal space. In this Review, we provide a biology-focused overview of how metastatic cells reach the leptomeninges, thrive in this nutritionally sparse environment and evade the detection of the omnipresent immune system.

Anatomical correlates for the newly discovered meningeal layer in the existing literature: A systematic review

The existence of a previously unrecognized subarachnoid lymphatic-like membrane (SLYM) was reported in a recent study. SLYM is described as an intermediate leptomeningeal layer between the arachnoid and pia mater in mouse and human brains, which divides the subarachnoid space (SAS) into two functional compartments. Being a macroscopic structure, having missed detection in previous studies is surprising. We systematically reviewed the published reports in animals and humans to explore whether prior descriptions of this meningeal layer were reported in some way. A comprehensive search was conducted in PubMed/Medline, EMBASE, Google Scholar, Science Direct, and Web of Science databases using combinations of MeSH terms and keywords with Boolean operators from inception until 31 December 2023. We found at least eight studies that provided structural evidence of an intermediate leptomeningeal layer in the brain or spinal cord. However, unequivocal descriptions for this layer all along the central nervous system were scarce. Obscure names like the epipial, intermediate meningeal, outer pial layers, or intermediate lamella were used to describe it. Its microscopic/ultrastructural details closely resemble the recently reported SLYM. We further examined the counterarguments in current literature that are skeptical of the existence of this layer. The potential physiological and clinical implications of this new meningeal layer are significant, underscoring the urgent need for further exploration of its structural and functional details.

A novel perspective of calvarial development: the cranial morphogenesis and differentiation regulated by dura mater

There are lasting concerns on calvarial development because cranium not only accommodates the growing brain, but also safeguards it from exogenous strikes. In the past decades, most studies attributed the dynamic expansion and remodeling of cranium to the proliferation of osteoprecursors in cranial primordium, and the proliferation of osteoprogenitors at the osteogenic front of cranial suture mesenchyme. Further investigations identified series genes expressed in suture mesenchymal cells as the markers of the progenitors, precursors and postnatal stem cells in cranium. However, similar to many other organs, it is suggested that the reciprocal interactions among different tissues also play essential roles in calvarial development. Actually, there are increasing evidence indicating that dura mater (DM) is indispensable for the calvarial morphogenesis and osteogenesis by secreting multiple growth factors, cytokines and extracellular matrix (ECM). Thus, in this review, we first briefly introduce the development of cranium, suture and DM, and then, comprehensively summarize the latest studies exploring the involvement of ECM in DM and cranium development. Eventually, we discussed the reciprocal interactions between calvarium and DM in calvarial development. Actually, our review provides a novel perspective for cranium development by integrating previous classical researches with a spotlight on the mutual interplay between the developing DM and cranium.

A low-swelling hydrogel as a multirole sealant for efficient dural defect sealing and prevention of postoperative adhesion

Dural defects and subsequent complications, including cerebrospinal fluid (CSF) leakage, are common in both spine surgery and neurosurgery, and existing clinical treatments are still unsatisfactory. In this study, a tissue-adhesive and low-swelling hydrogel sealant comprising gelatin and o-phthalaldehyde (OPA)-terminated 4-armed poly(ethylene glycol) (4aPEG-OPA) is developed via the OPA/amine condensation reaction. The hydrogel shows an adhesive strength of 79.9 ± 12.0 kPa on porcine casing and a burst pressure of 208.0 ± 38.0 cmH2O. The hydrogel exhibits a low swelling ratio at physiological conditions, avoiding nerve compression in the limited spinal and intracranial spaces. In rat and rabbit models of lumbar and cerebral dural defects, the 4aPEG-OPA/gelatin hydrogel achieves excellent performance in dural defect sealing and preventing CSF leakage. Moreover, local inflammation, epidural fibrosis and postoperative adhesion in the defect areas are markedly reduced. Thus, these findings establish the strong potential of the hydrogel sealant for the effective watertight closure of dural defects.

An Extensive Study Regarding the Microscopic Anatomy of the Early Fetal Human Optic Nerve

The development of the optic nerve and its surrounding tissues during the early fetal period is a convoluted period because it spans both the organogenesis period and the fetal period. This study details the microscopic anatomy and histoembryology of the optic nerve in embryos during the early fetal period, including the second half of the first trimester of pregnancy. Serial sections through the orbit of variously aged embryos allowed us to analyze the nerve in both longitudinal and transverse aspects. A histological assessment and description of the structures surrounding and inside the nerve were performed, highlighting the cellular subtypes involved. By employing immunohistochemical techniques, we could characterize the presence and distribution of astrocytes within the optic nerve. Our findings suggest that by the 8th gestational week (WG) the structures are homologs to all the adult ones but with an early appearance so that maturation processes take place afterward. By this age, the axons forming the nerve are definitive adult axons. The glial cells do not yet exhibit adult phenotype, but their aspect becomes adult toward the 13th week. During its development the optic nerve increases in size then, at 14 weeks, it shrinks considerably, possibly through its neural maturation process. The morphological primordium of the blood-nerve barrier can be first noted at 10 WG and at 13 WG the morphological blood-nerve barrier is definitive. The meningeal primordium can be first noted as a layer of agglomerated fibroblasts, later toward 13 WG splitting in pachymeninx and leptomeninges and leaving space for intrinsic blood vessels.

Functional analysis and transcriptome profile of meninges and skin fibroblasts from human-aged donors

The central nervous system (CNS) is surrounded by three membranes called meninges. Specialised fibroblasts, originating from the mesoderm and neural crest, primarily populate the meninges and serve as a binding agent. Our goal was to compare fibroblasts from meninges and skin obtained from the same human-aged donors, exploring their molecular and cellular characteristics related to CNS functions. We isolated meningeal fibroblasts (MFs) from brain donors and skin fibroblasts (SFs) from the same subjects. A functional analysis was performed measuring cell appearance, metabolic activity, and cellular orientation. We examined fibronectin, serpin H1, β-III-tubulin, and nestin through qPCR and immunofluorescence. A whole transcriptome analysis was also performed to characterise the gene expression of MFs and SFs. MFs appeared more rapidly in the post-tissue processing, while SFs showed an elevated cellular metabolism and a well-defined cellular orientation. The four markers were mostly similar between the MFs and SFs, except for nestin, more expressed in MFs. Transcriptome analysis reveals significant differences, particularly in cyclic adenosine monophosphate (cAMP) metabolism and response to forskolin, both of which are upregulated in MFs. This study highlights MFs' unique characteristics, including the timing of appearance, metabolic activity, and gene expression patterns, particularly in cAMP metabolism and response to forskolin. These findings contribute to a deeper understanding of non-neuronal cells' involvement in CNS activities and potentially open avenues for therapeutic exploration.

A rare case report of infratentorial cisternal angiolipoma with review of literature

Angiolipomas are slow-growing benign mesenchymal-derived tumors consisting of mature adipocytes and thin-walled blood vessels. While the majority of angiolipomas are found in subcutaneous tissues, rarely there are case reports of intracranial lesions. We present a case of cisternal angiolipoma in a 10-year-old female. She presented with vague symptoms like dizziness without neurological deficits and radiological evaluation confirmed a left-sided infratentorial cisternal partially enhancing mass. She underwent craniotomy and had complete resection of the mass, which was histologically composed of mature adipocytes and blood vessels, consistent with angiolipoma. A review of the literature found only 18 cases of intracranial angiolipoma ever reported with our case representing the first case of infratentorial cisternal region.

Cranial suture lineage and contributions to repair of the mouse skull

The cranial sutures are proposed to be a stem cell niche, harbouring skeletal stem cells that are directly involved in development, homeostasis and healing. Like the craniofacial bones, the sutures are formed from both mesoderm and neural crest. During cranial bone repair, neural crest cells have been proposed to be key players; however, neural crest contributions to adult sutures are not well defined, and the relative importance of suture proximity is unclear. Here, we use genetic approaches to re-examine the neural crest-mesoderm boundaries in the adult mouse skull. These are combined with calvarial wounding experiments suggesting that suture proximity improves the efficiency of cranial repair. Furthermore, we demonstrate that Gli1+ and Axin2+ skeletal stem cells are present in all calvarial sutures examined. We propose that the position of the defect determines the availability of neural crest-derived progenitors, which appear to be a key element in the repair of calvarial defects.

Postnatal meningeal CSF transport is primarily mediated by the arachnoid and pia maters and is not altered after intraventricular hemorrhage-posthemorrhagic hydrocephalus

BACKGROUND

CSF has long been accepted to circulate throughout the subarachnoid space, which lies between the arachnoid and pia maters of the meninges. How the CSF interacts with the cellular components of the developing postnatal meninges including the dura, arachnoid, and pia of both the meninges at the surface of the brain and the intracranial meninges, prior to its eventual efflux from the cranium and spine, is less understood. Here, we characterize small and large CSF solute distribution patterns along the intracranial and surface meninges in neonatal rodents and compare our findings to meningeal CSF solute distribution in a rodent model of intraventricular hemorrhage-posthemorrhagic hydrocephalus. We also examine CSF solute interactions with the tela choroidea and its pial invaginations into the choroid plexuses of the lateral, third, and fourth ventricles.

METHODS

1.9-nm gold nanoparticles, 15-nm gold nanoparticles, or 3 kDa Red Dextran Tetramethylrhodamine constituted in aCSF were infused into the right lateral ventricle of P7 rats to track CSF circulation. 10 min post-1.9-nm gold nanoparticle and Red Dextran Tetramethylrhodamine injection and 4 h post-15-nm gold nanoparticle injection, animals were sacrificed and brains harvested for histologic analysis to identify CSF tracer localization in the cranial and spine meninges and choroid plexus. Spinal dura and leptomeninges (arachnoid and pia) wholemounts were also evaluated.

RESULTS

There was significantly less CSF tracer distribution in the dura compared to the arachnoid and pia maters in neonatal rodents. Both small and large CSF tracers were transported intracranially to the arachnoid and pia mater of the perimesencephalic cisterns and tela choroidea, but not the falx cerebri. CSF tracers followed a similar distribution pattern in the spinal meninges. In the choroid plexus, there was large CSF tracer distribution in the apical surface of epithelial cells, and small CSF tracer along the basolateral surface. There were no significant differences in tracer intensity in the intracranial meninges of control vs. intraventricular hemorrhage-posthemorrhagic hydrocephalus (PHH) rodents, indicating preserved meningeal transport in the setting of PHH.

CONCLUSIONS

Differential CSF tracer handling by the meninges suggests that there are distinct roles for CSF handling between the arachnoid-pia and dura maters in the developing brain. Similarly, differences in apical vs. luminal choroid plexus CSF handling may provide insight into particle-size dependent CSF transport at the CSF-choroid plexus border.

Lateralized response of skull bone marrow via osteopontin signaling in mice after ischemia reperfusion

Skull bone marrow is thought to be an immune tissue closely associated with the central nervous system (CNS). Recent studies have focused on the role of skull bone marrow in central nervous system disorders. In this study, we performed single-cell RNA sequencing on ipsilateral and contralateral skull bone marrow cells after experimental stroke and then performed flow cytometry and analysis of cytokine expression. Skull marrow showed lateralization in response to stroke. Lateralization is demonstrated primarily by the proliferation and differentiation of myeloid and lymphoid lineage cells in the skull bone marrow adjacent to the ischemic region, with an increased proportion of neutrophils compared to monocytes. Analysis of chemokines in the skull revealed marked differences in chemotactic signals between the ipsilateral and contralateral skull, whereas sympathetic signals innervating the skull did not affect cranial bone marrow lateralization. Osteopontin (OPN) is involved in region-specific activation of the skull marrow that promotes inflammation in the meninges, and inhibition of OPN expression improves neurological function.

The Influence of Extracellular Vesicles Secreted by Dural Cells on Osteoblasts

To explore the influence of extracellular vesicles secreted by dural cells (Dura-EVs) on osteoblasts. Our methodology involves assessing the effects of these EVs at concentrations of 50ug/ml, 100ug/ml, and 200ug/ml on osteoblasts proliferation, differentiation, migration, osteogenesis, and inhibition of apoptosis. We also treated a cranial defect model with injections of these Dura-EVs and monitored the healing rate of cranial defects. Tissue sections were analyzed using Hematoxylin and Eosin (H & E), Masson's trichrome, and immunofluorescence (IF) staining. Our results suggest that Dura-EVs can enhance osteoblasts proliferation, migration, differentiation, and osteogenesis in a dose-dependent manner in vitro. In vivo, Dura-EVs may promote the repair of skull defects. Dura-EVs have an important influence on osteoblasts, our findings shed light on a novel aspect of the dura mater's contribution to cranial osteogenesis.

Skull progenitor cell-driven meningeal lymphatic restoration improves neurocognitive functions in craniosynostosis

The meninges lie in the interface between the skull and brain, harboring lymphatic vasculature and skull progenitor cells (SPCs). How the skull and brain communicate remains largely unknown. We found that impaired meningeal lymphatics and brain perfusion drive neurocognitive defects in Twist1+/- mice, an animal model of craniosynostosis recapitulating human Saethre-Chotzen syndrome. Loss of SPCs leads to skull deformities and elevated intracranial pressure (ICP), whereas transplanting SPCs back into mutant mice mitigates lymphatic and brain defects through two mechanisms: (1) decreasing elevated ICP by skull correction and (2) promoting the growth and migration of lymphatic endothelial cells (LECs) via SPC-secreted vascular endothelial growth factor-C (VEGF-C). Treating Twist1+/- mice with VEGF-C promotes meningeal lymphatic growth and rescues defects in ICP, brain perfusion, and neurocognitive functions. Thus, the skull functionally integrates with the brain via meningeal lymphatics, which is impaired in craniosynostosis and can be restored by SPC-driven lymphatic activation via VEGF-C.

In vitro response of dental pulp stem cells to dural substitute grafts: Analysis of cytocompatibility and bioactivity

AIM

The objective of this study was to assess and compare the cytocompatibility of decellularized porcine small intestine submucosal dural graft from Biodesign (BD) and polyester urethane-based Neuro-Patch (NP) dural substitute with the mineral trioxide aggregate (MTA) and the cyanoacrylate-based Histoacryl surgical adhesive. Furthermore, the study evaluated the inflammatory response and osteogenic differentiation of human dental pulp stem cells (hDPSCs) when cultured in direct contact with the dural substitutes in comparison with MTA.

METHODOLOGY

The viability of hDPSCs in direct contact with the tested materials was investigated in vitro by a CCK-8 assay. Additionally, the effects of dural substitutes and MTA on the expression of the inflammatory mediator interleukin-6 (IL-6) was investigated via enzyme-linked immunosorbent assay (ELISA), whilst effects on the differentiation were evaluated using alizarin red staining, alkaline phosphatase staining, ELISA and energy-dispersive X-ray elemental mapping.

RESULTS

The dural substitutes were cytocompatible and promoted cellular adhesion. The Histoacryl and MTA demonstrated cytotoxicity in fresh preparations but showed a more favourable cellular reaction when set. Investigations of biological activity indicated that dural substitute membranes did not induce an inflammatory response or osteogenic differentiation of hDPSCs. In contrast, MTA induced the expression of IL-6 and alkaline phosphatase activity contributing to enhanced differentiation and mineralization.

CONCLUSIONS

The dural substitute membranes showed cytocompatibility, did not provoke an inflammatory response and maintained the stemness of hDPSCs better than MTA. Additionally, the set Histoacryl surgical adhesive demonstrated good biocompatibility. Taken together, these results highlight the potential use of dural substitutes in regenerative endodontic procedures as coronal barriers alternative to MTA to reduce the incidence of intracanal calcifications.

Subdural osteoma in an adolescent patient with epilepsy: an unusual case report and literature review

OBJECTIVE

Subdural osteoma (SO) is a rarely reported benign tumor, and there is no report of SO manifested with epileptic seizures. We aim to further the understanding of SO-related epilepsy.

METHODS

Here, we report a meaningful case of epilepsy secondary to SO. A systematic review of the literature about SO using the electronic database PubMed and Web of science up to December 2022 was conducted.

RESULTS

A 15-year-old girl presented with epileptic seizures for 8 years. Magnetic resonance imaging revealed an irregular lesion with heterogeneous signal in the right frontal convexity. Right frontal craniotomy was performed to remove the lesion. The pathological diagnosis was SO. Histological analysis revealed that the mechanosensitive ion channels Piezo 1/2 were upregulated in the brain tissue compressed by the osteoma, compared with the levels in the osteoma-free region. Seizure freedom was obtained during the 6-month follow-up after the surgery. We identified 24 cases of SO in 23 articles. With our case, a total of 25 cases with 32 SOs was included. Of 25 cases, 24 are adults, and 1 is a child. Seizure has been reported only in our case. Frontal osteoma was found in 76% of the patients. Symptoms were cured in 56% of the patients after surgery.

CONCLUSION

Surgery is a safe and effective approach to the treatment of symptomatic osteoma. Mechanical compression on cerebral cortex may be a predisposing factor of the epileptogenesis caused by the SO.

Proteomic interrogation of the meninges reveals the molecular identities of structural components and regional distinctions along the CNS axis

The meninges surround the brain and spinal cord, affording physical protection while also serving as a niche of neuroimmune activity. Though possessing stromal qualities, its complex cellular and extracellular makeup has yet to be elaborated, and it remains unclear whether the meninges vary along the neuroaxis. Hence, studies were carried-out to elucidate the protein composition and structural organization of brain and spinal cord meninges in normal, adult Biozzi ABH mice. First, shotgun, bottom-up proteomics was carried-out. Prominent proteins at both brain and spinal levels included Type II collagen and Type II keratins, representing extracellular matrix (ECM) and cytoskeletal categories, respectively. While the vast majority of total proteins detected was shared between both meningeal locales, more were uniquely detected in brain than in spine. This pattern was also seen when total proteins were subdivided by cellular compartment, except in the case of the ECM category where brain and spinal meninges each had near equal number of unique proteins, and Type V and type III collagen registered exclusively in the spine. Quantitative analysis revealed differential expression of several collagens and cytoskeletal proteins between brain and spinal meninges. High-resolution immunofluorescence and immunogold-scanning electronmicroscopy on sections from whole brain and spinal cord - still encased within bone -identified major proteins detected by proteomics, and highlighted their association with cellular and extracellular elements of variously shaped arachnoid trabeculae. Western blotting aligned with the proteomic and immunohistological analyses, reinforcing differential appearance of proteins in brain vs spinal meninges. Results could reflect regional distinctions in meninges that govern protective and/or neuroimmune functions.

The SWI/SNF Complex in Neural Crest Cell Development and Disease

While the neural crest cell population gives rise to an extraordinary array of derivatives, including elements of the craniofacial skeleton, skin pigmentation, and peripheral nervous system, it is today increasingly recognized that Schwann cell precursors are also multipotent. Two mammalian paralogs of the SWI/SNF (switch/sucrose nonfermentable) chromatin-remodeling complexes, BAF (Brg1-associated factors) and PBAF (polybromo-associated BAF), are critical for neural crest specification during normal mammalian development. There is increasing evidence that pathogenic variants in components of the BAF and PBAF complexes play central roles in the pathogenesis of neural crest-derived tumors. Transgenic mouse models demonstrate a temporal window early in development where pathogenic variants in Smarcb1 result in the formation of aggressive, poorly differentiated tumors, such as rhabdoid tumors. By contrast, later in development, homozygous inactivation of Smarcb1 requires additional pathogenic variants in tumor suppressor genes to drive the development of differentiated adult neoplasms derived from the neural crest, which have a comparatively good prognosis in humans.

Anatomical network modules of the human central nervous-craniofacial skeleton system

Anatomical network analysis (AnNA) is a systems biological framework based on network theory that enables anatomical structural analysis by incorporating modularity to model structural complexity. The human brain and facial structures exhibit close structural and functional relationships, suggestive of a co-evolved anatomical network. The present study aimed to analyze the human head as a modular entity that comprises the central nervous system, including the brain, spinal cord, and craniofacial skeleton. An AnNA model was built using 39 anatomical nodes from the brain, spinal cord, and craniofacial skeleton. The linkages were identified using peripheral nerve supply and direct contact between structures. The Spinglass algorithm in the igraph software was applied to construct a network and identify the modules of the central nervous system-craniofacial skeleton anatomical network. Two modules were identified. These comprised an anterior module, which included the forebrain, anterior cranial base, and upper-middle face, and a posterior module, which included the midbrain, hindbrain, mandible, and posterior cranium. These findings may reflect the genetic and signaling networks that drive the mosaic central nervous system and craniofacial development and offer important systems biology perspectives for developmental disorders of craniofacial structures.

Lineage-specific mutation of Lmx1b provides new insights into distinct regulation of suture development in different areas of the calvaria

The calvaria (top part of the skull) is made of pieces of bone as well as multiple soft tissue joints called sutures. The latter is crucial to the growth and morphogenesis of the skull, and thus a loss of calvarial sutures can lead to severe congenital defects in humans. During embryogenesis, the calvaria develops from the cranial mesenchyme covering the brain, which contains cells originating from the neural crest and the mesoderm. While the mechanism that patterns the cranial mesenchyme into bone and sutures is not well understood, function of Lmx1b, a gene encoding a LIM-domain homeodomain transcription factor, plays a key role in this process. In the current study, we investigated a difference in the function of Lmx1b in different parts of the calvaria using neural crest-specific and mesoderm-specific Lmx1b mutants. We found that Lmx1b was obligatory for development of the interfrontal suture and the anterior fontanel along the dorsal midline of the skull, but not for the posterior fontanel over the midbrain. Also, Lmx1b mutation in the neural crest-derived mesenchyme, but not the mesoderm-derived mesenchyme, had a non-cell autonomous effect on coronal suture development. Furthermore, overexpression of Lmx1b in the neural crest lineage had different effects on the position of the coronal suture on the apical part and the basal part. Other unexpected phenotypes of Lmx1b mutants led to an additional finding that the coronal suture and the sagittal suture are of dual embryonic origin. Together, our data reveal a remarkable level of regional specificity in regulation of calvarial development.

Production of Blended Poly(acrylonitrile): Poly(ethylenedioxythiophene):Poly(styrene sulfonate) Electrospun Fibers for Neural Applications

This study describes, for the first time, the successful incorporation of poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) in Poly(acrylonitrile) (PAN) fibers. While electroconductive PEDOT:PSS is extremely challenging to electrospun into fibers. Therefore, PAN, a polymer easy to electrospun, was chosen as a carrier due to its biocompatibility and tunable chemical stability when cross-linked, particularly using strong acids. PAN:PEDOT:PSS blends, prepared from PEDOT:PSS Clevios PH1000, were electrospun into fibers (PH1000) with a diameter of 515 ± 120 nm, which after being thermally annealed (PH1000 24H) and treated with heated sulfuric acid (PH1000 H₂SO₄), resulted in fibers with diameters of 437 ± 109 and 940 ± 210 nm, respectively. The fibers obtained over the stepwise process were characterized through infra-red/Raman spectroscopy and cyclic voltammetry. The final fiber meshes showed enhanced electroconductivity (3.2 × 10^-3 S cm^-1, four-points-assay). Fiber meshes biocompatibility was evaluated using fibroblasts and neural stem cells (NSCs) following, respectively, the ISO10993 guidelines and standard adhesion/proliferation assay. NSCs cultured on PH1000 H₂SO₄ fibers presented normal morphology and high proliferation rates (0.37 day^-1 vs. 0.16 day^-1 for culture plate), indicating high biocompatibility for NSCs. Still, the low initial NSC adhesion of 7% calls for improving seeding methodologies. PAN:PEDOT:PSS fibers, here successful produced for the first time, have potential applications in neural tissue engineering and soft electronics.

Vascular anomaly, lipoma, and polymicrogyria associated with schizencephaly: developmental and diagnostic insights. Illustrative case

BACKGROUND

Schizencephaly is an uncommon central nervous system malformation. Intracranial lipomas are also rare, accounting for approximately 0.1% of brain "tumors." They are believed to be derived from a persistent meninx primitiva, a neural crest-derived mesenchyme that develops into the dura and leptomeninges.

OBSERVATIONS

The authors present a case of heterotopic adipose tissue and a nonshunting arterial vascular malformation arising within a schizencephalic cleft in a 22-year-old male. Imaging showed right frontal gray matter abnormality and an associated suspected arteriovenous malformation with evidence of hemorrhage. Brain magnetic resonance imaging revealed right frontal polymicrogyria lining an open-lip schizencephaly, periventricular heterotopic gray matter, fat within the schizencephalic cleft, and gradient echo hypointensity concerning for prior hemorrhage. Histological assessment demonstrated mature adipose tissue with large-bore, thick-walled, irregular arteries. Mural calcifications and subendothelial cushions suggesting nonlaminar blood flow were observed. There were no arterialized veins or direct transitions from the arteries to veins. Hemosiderin deposition was scant, and hemorrhage was not present. The final diagnosis was consistent with ectopic mature adipose tissue and arteries with meningocerebral cicatrix.

LESSONS

This example of a complex maldevelopment of derivatives of the meninx primitiva in association with cortical maldevelopment highlights the unique challenges from both a radiological and histological perspective during diagnostic workup.

Pleiotropic role of TRAF7 in skull-base meningiomas and congenital heart disease

While somatic variants of TRAF7 (Tumor necrosis factor receptor-associated factor 7) underlie anterior skull-base meningiomas, here we report the inherited mutations of TRAF7 that cause congenital heart defects. We show that TRAF7 mutants operate in a dominant manner, inhibiting protein function via heterodimerization with wild-type protein. Further, the shared genetics of the two disparate pathologies can be traced to the common origin of forebrain meninges and cardiac outflow tract from the TRAF7-expressing neural crest. Somatic and inherited mutations disrupt TRAF7-IFT57 interactions leading to cilia degradation. TRAF7-mutant meningioma primary cultures lack cilia, and TRAF7 knockdown causes cardiac, craniofacial, and ciliary defects in Xenopus and zebrafish, suggesting a mechanistic convergence for TRAF7-driven meningiomas and developmental heart defects.

Stuck on you: Meninges cellular crosstalk in development

The spatial and temporal development of the brain, overlying meninges (fibroblasts, vasculature and immune cells) and calvarium are highly coordinated. In particular, the timing of meningeal fibroblasts into molecularly distinct pia, arachnoid and dura subtypes coincides with key developmental events in the brain and calvarium. Further, the meninges are positioned to influence development of adjacent structures and do so via depositing basement membrane and producing molecular cues to regulate brain and calvarial development. Here, we review the current knowledge of how meninges development aligns with events in the brain and calvarium and meningeal fibroblast "crosstalk" with these structures. We summarize outstanding questions and how the use of non-mammalian models to study the meninges will substantially advance the field of meninges biology.

Leptomeningeal Disease (LMD) in Patients with Melanoma Metastases

Leptomeningeal disease (LMD) is a devastating complication caused by seeding malignant cells to the cerebrospinal fluid (CSF) and the leptomeningeal membrane. LMD is diagnosed in 5-15% of patients with systemic malignancy. Management of LMD is challenging due to the biological and metabolic tumor microenvironment of LMD being largely unknown. Patients with LMD can present with a wide variety of signs and/or symptoms that could be multifocal and include headache, nausea, vomiting, diplopia, and weakness, among others. The median survival time for patients with LMD is measured in weeks and up to 3-6 months with aggressive management, and death usually occurs due to progressive neurologic dysfunction. In melanoma, LMD is associated with a suppressive immune microenvironment characterized by a high number of apoptotic and exhausted CD4⁺ T-cells, myeloid-derived suppressor cells, and a low number of CD8⁺ T-cells. Proteomics analysis revealed enrichment of complement cascade, which may disrupt the blood-CSF barrier. Clinical management of melanoma LMD consists primarily of radiation therapy, BRAF/MEK inhibitors as targeted therapy, and immunotherapy with anti-PD-1, anti-CTLA-4, and anti-LAG-3 immune checkpoint inhibitors. This review summarizes the biology and anatomic features of melanoma LMD, as well as the current therapeutic approaches.

Recent topics regarding macrophage in the central nervous system

The central nervous system (CNS) is a highly complex collection of neurons with a variety of stromal cells, such as glia cells, immune cells, vascular cells and fibroblasts. Microglia are a resident macrophage and a type of glial cells located in the parenchyma of the CNS and play a pivotal role in the maintenance of tissue homeostasis. They are early responders to the abnormality of the CNS, leading to the adaptation of their phenotypes by virtue of their plasticity, after which they give an impact on neuronal functions. Besides microglia, there are anatomically and phenotypically distinct macrophage populations at the border of the CNS, such as meninge, perivascular space and choroid plexus, where they show distinct morphology and gene expression profiles when compared with microglia. This review will summarize the recent advance in our knowledge regarding their heterogeneity, plasticity, ontogenetic relationship of these CNS-resident macrophage populations.

Torcular pseudomass is frequently detected on fetal magnetic resonance imaging and reduces with gestational age

BACKGROUND

The torcular pseudomass is an incidental extra-axial midline mass located between the venous sinuses and the occipital squama in the pediatric population. Although this structure is presumed to be a developmental feature, it has not been characterized on fetal MRI.

OBJECTIVE

To determine the frequency, imaging features and longitudinal in utero evolution of torcular pseudomass using fetal MRI.

MATERIALS AND METHODS

We present a single-center retrospective study of fetal MRI performed at a tertiary hospital. Two independent reviewers first ordinally scored torcular pseudomass as absent, focal, crescentic or bulky based on morphology. We reviewed available follow-up fetal and postnatal MRI and further classified torcular pseudomass as stable, involuted or progressive. We also collected clinical and demographic data from electronic charts and compared them among categories, corrected for multiple comparisons.

RESULTS

This study included a total of 219 fetuses with median gestational age of 28 weeks (interquartile range [IQR]: 23-32 weeks). Torcular pseudomass was absent in 8% (n=17) and present as a focal mass in 15% (n=33), crescentic in 45% (n=98) and bulky in 32% (n=71) of the cases. Median gestational age was statistically different among torcular pseudomass categories and inversely associated with size. Follow-up fetal MRI was available in 9.6% (n=21) of cases (median interval 4 weeks; IQR: 2-9 weeks) and torcular pseudomass in these cases was classified as stable in 67% (n=14), involuted in 29% (n=6) and progressive in 5% (n=1). Postnatal MRI was available in 5% (n=12) of fetuses (median interval 11.5 months, IQR: 3-17 months), and among these cases torcular pseudomass was classified as stable in 33% (n=4) and involuted in 67% (n=8).

CONCLUSION

Torcular pseudomass is highly prevalent in the fetal population and shows a natural tendency to involute, even in utero, although it sometimes persists during early infanthood.

Mechanisms of myeloid cell entry to the healthy and diseased central nervous system

Myeloid cells in the central nervous system (CNS), such as microglia, CNS-associated macrophages (CAMs), dendritic cells and monocytes, are vital for steady-state immune homeostasis as well as the resolution of tissue damage during brain development or disease-related pathology. The complementary usage of multimodal high-throughput and high-dimensional single-cell technologies along with recent advances in cell-fate mapping has revealed remarkable myeloid cell heterogeneity in the CNS. Despite the establishment of extensive expression profiles revealing myeloid cell multiplicity, the local anatomical conditions for the temporal- and spatial-dependent cellular engraftment are poorly understood. Here we highlight recent discoveries of the context-dependent mechanisms of myeloid cell migration and settlement into distinct subtissular structures in the CNS. These insights offer better understanding of the factors needed for compartment-specific myeloid cell recruitment, integration and residence during development and perturbation, which may lead to better treatment of CNS diseases.

Molecular Mechanisms Involved in Craniosynostosis

Craniosynostosis refers to the early fusion of one or many cranial sutures, causing craniofacial abnormalities observed in 1:2,500 births worldwide. In most cases (85%), craniosynostosis is presented as sporadic anomaly (non-syndromic craniosynostosis), while in other cases (15%) as part of syndromes (syndromic craniosynostosis). Patients with syndromic disorder usually have more severe symptoms compared to those with single suture synostosis. Most common syndromes of craniosynostosis include Pfeiffer, Apert, Crouzon, Jackson-Weiss, Muenke and Boston type MSX2-related syndrome. The main gene mutations in craniosynostosis involve FGFR1, FGFR2, FGFR3, TWIST1 and MSX2, which encode key factors influencing cranial bone morphogenesis. The main therapeutic approaches are surgical as discussed in this review, and the type of therapy depends on the graveness of the incident.

Creating morphological diversity in reptilian temporal skull region: A review of potential developmental mechanisms

Reptilian skull morphology is highly diverse and broadly categorized into three categories based on the number and position of the temporal fenestrations: anapsid, synapsid, and diapsid. According to recent phylogenetic analysis, temporal fenestrations evolved twice independently in amniotes, once in Synapsida and once in Diapsida. Although functional aspects underlying the evolution of tetrapod temporal fenestrations have been well investigated, few studies have investigated the developmental mechanisms responsible for differences in the pattern of temporal skull region. To determine what these mechanisms might be, we first examined how the five temporal bones develop by comparing embryonic cranial osteogenesis between representative extant reptilian species. The pattern of temporal skull region may depend on differences in temporal bone growth rate and growth direction during ontogeny. Next, we compared the histogenesis patterns and the expression of two key osteogenic genes, Runx2 and Msx2, in the temporal region of the representative reptilian embryos. Our comparative analyses suggest that the embryonic histological condition of the domain where temporal fenestrations would form predicts temporal skull morphology in adults and regulatory modifications of Runx2 and Msx2 expression in osteogenic mesenchymal precursor cells are likely involved in generating morphological diversity in the temporal skull region of reptiles.

Neuroimmune signaling at the brain borders

The central nervous system (CNS) has been viewed as an immunologically privileged site, but emerging works are uncovering a large array of neuroimmune interactions primarily occurring at its borders. CNS barriers sites host diverse population of both innate and adaptive immune cells capable of, directly and indirectly, influence the function of the residing cells of the brain parenchyma. These structures are only starting to reveal their role in controlling brain function under normal and pathological conditions and represent an underexplored therapeutic target for the treatment of brain disorders. This review will highlight the development of the CNS barriers to host neuro-immune interactions and emphasize their newly described roles in neurodevelopmental, neurological, and neurodegenerative disorders, particularly for the meninges.

HOXC10 intronic duplication is associated with unsealed skull and crest in crested chicken with cerebral hernia

The genetic basis and developmental mechanism of unsealed skull in crested chicken with cerebral hernia remain unclear. Here, a genomic region including six HOXC genes was mapped by bulked segregant analysis (BSA) in a crested chicken resource population. A 195-bp intronic tandem duplication was further confirmed in the HOXC10 gene. HOXC genes, particularly HOXC10, were expressed ectopically in fetal skin and meningeal tissues of crested chicken with cerebral hernia, indicating its impact on the cranial mesenchymal tissues that drive the development of scalp skin, frontal bone, and meninges. The restricted expansion of frontal bone progenitors labeled with anti-RUNX2 antibody in the supraorbital mesenchyme of the fetal head implied abnormal migration, which contributed to the formation of the unsealed skull. This study suggests that HOXC genes were potent drivers for the abnormalities of the head crest and unsealed skull observed in crested chicken with cerebral hernia.

Single-cell atlas of craniogenesis uncovers SOXC-dependent, highly proliferative, and myofibroblast-like osteodermal progenitors

The mammalian skull vault is essential to shape the head and protect the brain, but the cellular and molecular events underlying its development remain incompletely understood. Single-cell transcriptomic profiling from early to late mouse embryonic stages provides a detailed atlas of cranial lineages. It distinguishes various populations of progenitors and reveals a high expression of SOXC genes (encoding the SOX4, SOX11, and SOX12 transcription factors) early in development in actively proliferating and myofibroblast-like osteodermal progenitors. SOXC inactivation in these cells causes severe skull and skin underdevelopment due to the limited expansion of cell populations before and upon lineage commitment. SOXC genes enhance the expression of gene signatures conferring dynamic cellular and molecular properties, including actin cytoskeleton assembly, chromatin remodeling, and signaling pathway induction and responsiveness. These findings shed light onto craniogenic mechanisms and SOXC functions and suggest that similar mechanisms could decisively control many developmental, adult, pathological, and regenerative processes.

Angelozzi and colleagues establish a detailed transcriptomic atlas of mouse embryonic craniogenesis and use mutant mice to show that SOXC (SOX4, SOX11, and SOX12 transcription factors) critically support osteogenesis and dermogenesis by promoting the expression of dynamic cellular and molecular properties of progenitor populations. SOXC could similarly affect many other processes.

Molecular and Cellular Analysis of the Repair of Zebrafish Optic Tectum Meninges Following Laser Injury

We studied cell recruitment following optic tectum (OT) injury in zebrafish (Danio rerio), which has a remarkable ability to regenerate many of its organs, including the brain. The OT is the largest dorsal layered structure in the zebrafish brain. In juveniles, it is an ideal structure for imaging and dissection. We investigated the recruited cells within the juvenile OT during regeneration in a Pdgfrβ-Gal4:UAS-EGFP line in which pericytes, vascular, circulating, and meningeal cells are labeled, together with neurons and progenitors. We first performed high-resolution confocal microscopy and single-cell RNA-sequencing (scRNAseq) on EGFP-positive cells. We then tested three types of injury with very different outcomes (needle (mean depth in the OT of 200 µm); deep-laser (depth: 100 to 200 µm depth); surface-laser (depth: 0 to 100 µm)). Laser had the additional advantage of better mimicking of ischemic cerebral accidents. No massive recruitment of EGFP-positive cells was observed following laser injury deep in the OT. This type of injury does not perturb the meninx/brain–blood barrier (BBB). We also performed laser injuries at the surface of the OT, which in contrast create a breach in the meninges. Surprisingly, one day after such injury, we observed the migration to the injury site of various EGFP-positive cell types at the surface of the OT. The migrating cells included midline roof cells, which activated the PI3K-AKT pathway; fibroblast-like cells expressing numerous collagen genes and most prominently in 3D imaging; and a large number of arachnoid cells that probably migrate to the injury site through the activation of cilia motility genes, most likely being direct targets of the FOXJ1a gene. This study, combining high-content imaging and scRNAseq in physiological and pathological conditions, sheds light on meninges repair mechanisms in zebrafish that probably also operate in mammalian meninges.

Involvement of Mechanical Cues in the Migration of Cajal-Retzius Cells in the Marginal Zone During Neocortical Development

Emerging evidence points to coordinated action of chemical and mechanical cues during brain development. At early stages of neocortical development, angiogenic factors and chemokines such as CXCL12, ephrins, and semaphorins assume crucial roles in orchestrating neuronal migration and axon elongation of postmitotic neurons. Here we explore the intrinsic mechanical properties of the developing marginal zone of the pallium in the migratory pathways and brain distribution of the pioneer Cajal-Retzius cells. These neurons are generated in several proliferative regions in the developing brain (e.g., the cortical hem and the pallial subpallial boundary) and migrate tangentially in the preplate/marginal zone covering the upper portion of the developing cortex. These cells play crucial roles in correct neocortical layer formation by secreting several molecules such as Reelin. Our results indicate that the motogenic properties of Cajal-Retzius cells and their perinatal distribution in the marginal zone are modulated by both chemical and mechanical factors, by the specific mechanical properties of Cajal-Retzius cells, and by the differential stiffness of the migratory routes. Indeed, cells originating in the cortical hem display higher migratory capacities than those generated in the pallial subpallial boundary which may be involved in the differential distribution of these cells in the dorsal-lateral axis in the developing marginal zone.

Immunological defense of CNS barriers against infections

Neuroanatomical barriers with physical, chemical, and immunological properties play an essential role in preventing the spread of peripheral infections into the CNS. A failure to contain pathogens within these barriers can result in very serious CNS diseases. CNS barriers are inhabited by an elaborate conglomerate of innate and adaptive immune cells that are highly responsive to environmental challenges. The CNS and its barriers can also be protected by memory T and B cells elicited by prior infection or vaccination. Here, we discuss the different CNS barriers from a developmental, anatomical, and immunological standpoint and summarize our current understanding of how memory cells protect the CNS compartment. We then discuss a contemporary challenge to CNS-barrier system (SARS-CoV-2 infection) and highlight approaches to promote immunological protection of the CNS via vaccination.

Single-cell profiling of human dura and meningioma reveals cellular meningeal landscape and insights into meningioma immune response

BACKGROUND

Recent investigations of the meninges have highlighted the importance of the dura layer in central nervous system immune surveillance beyond a purely structural role. However, our understanding of the meninges largely stems from the use of pre-clinical models rather than human samples.

METHODS

Single-cell RNA sequencing of seven non-tumor-associated human dura samples and six primary meningioma tumor samples (4 matched and 2 non-matched) was performed. Cell type identities, gene expression profiles, and T cell receptor expression were analyzed. Copy number variant (CNV) analysis was performed to identify putative tumor cells and analyze intratumoral CNV heterogeneity. Immunohistochemistry and imaging mass cytometry was performed on selected samples to validate protein expression and reveal spatial localization of select protein markers.

RESULTS

In this study, we use single-cell RNA sequencing to perform the first characterization of both non-tumor-associated human dura and primary meningioma samples. First, we reveal a complex immune microenvironment in human dura that is transcriptionally distinct from that of meningioma. In addition, we characterize a functionally diverse and heterogenous landscape of non-immune cells including endothelial cells and fibroblasts. Through imaging mass cytometry, we highlight the spatial relationship among immune cell types and vasculature in non-tumor-associated dura. Utilizing T cell receptor sequencing, we show significant TCR overlap between matched dura and meningioma samples. Finally, we report copy number variant heterogeneity within our meningioma samples.

CONCLUSIONS

Our comprehensive investigation of both the immune and non-immune cellular landscapes of human dura and meningioma at single-cell resolution builds upon previously published data in murine models and provides new insight into previously uncharacterized roles of human dura.

Specification of CNS macrophage subsets occurs postnatally in defined niches

All tissue-resident macrophages of the central nervous system (CNS)-including parenchymal microglia, as well as CNS-associated macrophages (CAMs¹) such as meningeal and perivascular macrophages^2-7-are part of the CNS endogenous innate immune system that acts as the first line of defence during infections or trauma^2,8-10. It has been suggested that microglia and all subsets of CAMs are derived from prenatal cellular sources in the yolk sac that were defined as early erythromyeloid progenitors^11-15. However, the precise ontogenetic relationships, the underlying transcriptional programs and the molecular signals that drive the development of distinct CAM subsets in situ are poorly understood. Here we show, using fate-mapping systems, single-cell profiling and cell-specific mutants, that only meningeal macrophages and microglia share a common prenatal progenitor. By contrast, perivascular macrophages originate from perinatal meningeal macrophages only after birth in an integrin-dependent manner. The establishment of perivascular macrophages critically requires the presence of arterial vascular smooth muscle cells. Together, our data reveal a precisely timed process in distinct anatomical niches for the establishment of macrophage subsets in the CNS.

How Does the Immune System Enter the Brain?

Multiple Sclerosis (MS) is considered the most frequent inflammatory demyelinating disease of the central nervous system (CNS). It occurs with a variable prevalence across the world. A rich armamentarium of disease modifying therapies selectively targeting specific actions of the immune system is available for the treatment of MS. Understanding how and where immune cells are primed, how they access the CNS in MS and how immunomodulatory treatments affect neuroinflammation requires a proper knowledge on the mechanisms regulating immune cell trafficking and the special anatomy of the CNS. The brain barriers divide the CNS into different compartments that differ with respect to their accessibility to cells of the innate and adaptive immune system. In steady state, the blood-brain barrier (BBB) limits immune cell trafficking to activated T cells, which can reach the cerebrospinal fluid (CSF) filled compartments to ensure CNS immune surveillance. In MS immune cells breach a second barrier, the glia limitans to reach the CNS parenchyma. Here we will summarize the role of the endothelial, epithelial and glial brain barriers in regulating immune cell entry into the CNS and which immunomodulatory treatments for MS target the brain barriers. Finally, we will explore current knowledge on genetic and environmental factors that may influence immune cell entry into the CNS during neuroinflammation in Africa.

An Efficient Method for the Isolation and Cultivation of Hypothalamic Neural Stem/Progenitor Cells From Mouse Embryos

The hypothalamus is the key region that regulates the neuroendocrine system as well as instinct behaviors, and hypothalamic dysfunction causes refractory clinical problems. Recent studies have indicated that neural stem/progenitor cell (NSPC) in the hypothalamus play a crucial role in hypothalamic function. However, specific hypothalamic NSPC culture methods have not been established, especially not detailed or efficient surgical procedures. The present study presented a convenient, detailed and efficient method for the isolation and cultivation of hypothalamic NSPCs from embryonic day 12.5 mice. The procedure includes embryo acquisition, brain microdissection to quickly obtain hypothalamic tissue and hypothalamic NSPC culture. Hypothalamic NSPCs can be quickly harvested and grow well in both neurosphere and adherent cultures through this method. Additionally, we confirmed the cell origin and evaluated the proliferation and differentiation properties of cultured cells. In conclusion, we present a convenient and practical method for the isolation and cultivation of hypothalamic NSPCs that can be used in extensive hypothalamic studies.

Genomic Biomarkers of Meningioma: A Focused Review

Meningiomas represent a phenotypically and genetically diverse group of tumors which often behave in ways that are not simply explained by their pathologic grade. The genetic landscape of meningiomas has become a target of investigation as tumor genomics have been found to impact tumor location, recurrence risk, and malignant potential. Additionally, targeted therapies are being developed that in the future may provide patients with personalized chemotherapy based on the genetic aberrations within their tumor. This review focuses on the most common genetic mutations found in meningiomas of all grades, with an emphasis on the impact on tumor location and clinically relevant tumor characteristics. NF-2 and the non-NF-2 family of genetic mutations are summarized in the context of low-grade and high-grade tumors, followed by a comprehensive discussion regarding the genetic and embryologic basis for meningioma location and phenotypic heterogeneity. Finally, targeted therapies based on tumor genomics currently in use and under investigation are reviewed and future avenues for research are suggested. The field of meningioma genomics has broad implications on the way meningiomas will be treated in the future, and is gradually shifting the way clinicians approach this diverse group of tumors.

The developing mouse coronal suture at single-cell resolution

Sutures separate the flat bones of the skull and enable coordinated growth of the brain and overlying cranium. The coronal suture is most commonly fused in monogenic craniosynostosis, yet the unique aspects of its development remain incompletely understood. To uncover the cellular diversity within the murine embryonic coronal suture, we generated single-cell transcriptomes and performed extensive expression validation. We find distinct pre-osteoblast signatures between the bone fronts and periosteum, a ligament-like population above the suture that persists into adulthood, and a chondrogenic-like population in the dura mater underlying the suture. Lineage tracing reveals an embryonic Six2+ osteoprogenitor population that contributes to the postnatal suture mesenchyme, with these progenitors being preferentially affected in a Twist1+/-; Tcf12+/- mouse model of Saethre-Chotzen Syndrome. This single-cell atlas provides a resource for understanding the development of the coronal suture and the mechanisms for its loss in craniosynostosis.

Morphological and Functional Changes of Roof Plate Cells in Spinal Cord Development

The most dorsal region, or roof plate, is the dorsal organizing center of developing spinal cord. This region is also involved in development of neural crest cells, which are the source of migratory neural crest cells. During early development of the spinal cord, roof plate cells secrete signaling molecules, such as Wnt and BMP family proteins, which regulate development of neural crest cells and dorsal spinal cord. After the dorso-ventral pattern is established, spinal cord dynamically changes its morphology. With this morphological transformation, the lumen of the spinal cord gradually shrinks to form the central canal, a cavity filled with cerebrospinal fluid that is connected to the ventricular system of the brain. The dorsal half of the spinal cord is separated by a glial structure called the dorsal (or posterior) median septum. However, underlying mechanisms of such morphological transformation are just beginning to be understood. Recent studies reveal that roof plate cells dramatically stretch along the dorso-ventral axis, accompanied by reduction of the spinal cord lumen. During this stretching process, the tips of roof plate cells maintain contact with cells surrounding the shrinking lumen, eventually exposed to the inner surface of the central canal. Interestingly, Wnt expression remains in stretched roof plate cells and activates Wnt/β-catenin signaling in ependymal cells surrounding the central canal. Wnt/β-catenin signaling in ependymal cells promotes proliferation of neural progenitor and stem cells in embryonic and adult spinal cord. In this review, we focus on the role of the roof plate, especially that of Wnt ligands secreted by roof plate cells, in morphological changes occurring in the spinal cord.

Molecular architecture of the developing mouse brain

The mammalian brain develops through a complex interplay of spatial cues generated by diffusible morphogens, cell-cell interactions and intrinsic genetic programs that result in probably more than a thousand distinct cell types. A complete understanding of this process requires a systematic characterization of cell states over the entire spatiotemporal range of brain development. The ability of single-cell RNA sequencing and spatial transcriptomics to reveal the molecular heterogeneity of complex tissues has therefore been particularly powerful in the nervous system. Previous studies have explored development in specific brain regions^1-8, the whole adult brain⁹ and even entire embryos¹⁰. Here we report a comprehensive single-cell transcriptomic atlas of the embryonic mouse brain between gastrulation and birth. We identified almost eight hundred cellular states that describe a developmental program for the functional elements of the brain and its enclosing membranes, including the early neuroepithelium, region-specific secondary organizers, and both neurogenic and gliogenic progenitors. We also used in situ mRNA sequencing to map the spatial expression patterns of key developmental genes. Integrating the in situ data with our single-cell clusters revealed the precise spatial organization of neural progenitors during the patterning of the nervous system.

Cell-Type-Specific Gene Expression in Developing Mouse Neocortex: Intermediate Progenitors Implicated in Axon Development

Cerebral cortex projection neurons (PNs) are generated from intermediate progenitors (IPs), which are in turn derived from radial glial progenitors (RGPs). To investigate developmental processes in IPs, we profiled IP transcriptomes in embryonic mouse neocortex, using transgenic Tbr2-GFP mice, cell sorting, and microarrays. These data were used in combination with in situ hybridization to ascertain gene sets specific for IPs, RGPs, PNs, interneurons, and other neural and non-neural cell types. RGP-selective transcripts (n = 419) included molecules for Notch receptor signaling, proliferation, neural stem cell identity, apical junctions, necroptosis, hippo pathway, and NF-κB pathway. RGPs also expressed specific genes for critical interactions with meningeal and vascular cells. In contrast, IP-selective genes (n = 136) encoded molecules for activated Delta ligand presentation, epithelial-mesenchymal transition, core planar cell polarity (PCP), axon genesis, and intrinsic excitability. Interestingly, IPs expressed several “dependence receptors” (Unc5d, Dcc, Ntrk3, and Epha4) that induce apoptosis in the absence of ligand, suggesting a competitive mechanism for IPs and new PNs to detect key environmental cues or die. Overall, our results imply a novel role for IPs in the patterning of neuronal polarization, axon differentiation, and intrinsic excitability prior to mitosis. Significantly, IPs highly express Wnt-PCP, netrin, and semaphorin pathway molecules known to regulate axon polarization in other systems. In sum, IPs not only amplify neurogenesis quantitatively, but also molecularly “prime” new PNs for axogenesis, guidance, and excitability.

Living on the Edge of the CNS: Meninges Cell Diversity in Health and Disease

The meninges are the fibrous covering of the central nervous system (CNS) which contain vastly heterogeneous cell types within its three layers (dura, arachnoid, and pia). The dural compartment of the meninges, closest to the skull, is predominantly composed of fibroblasts, but also includes fenestrated blood vasculature, an elaborate lymphatic system, as well as immune cells which are distinct from the CNS. Segregating the outer and inner meningeal compartments is the epithelial-like arachnoid barrier cells, connected by tight and adherens junctions, which regulate the movement of pathogens, molecules, and cells into and out of the cerebral spinal fluid (CSF) and brain parenchyma. Most proximate to the brain is the collagen and basement membrane-rich pia matter that abuts the glial limitans and has recently be shown to have regional heterogeneity within the developing mouse brain. While the meninges were historically seen as a purely structural support for the CNS and protection from trauma, the emerging view of the meninges is as an essential interface between the CNS and the periphery, critical to brain development, required for brain homeostasis, and involved in a variety of diseases. In this review, we will summarize what is known regarding the development, specification, and maturation of the meninges during homeostatic conditions and discuss the rapidly emerging evidence that specific meningeal cell compartments play differential and important roles in the pathophysiology of a myriad of diseases including: multiple sclerosis, dementia, stroke, viral/bacterial meningitis, traumatic brain injury, and cancer. We will conclude with a list of major questions and mechanisms that remain unknown, the study of which represent new, future directions for the field of meninges biology.

Perivascular stromal cells: Directors of tissue immune niches

Perivascular niches are specialized microenvironments where stromal and immune cells interact with vasculature to monitor tissue status. Adventitial perivascular niches surround larger blood vessels and other boundary sites, supporting collections of immune cells, stromal cells, lymphatics, and neurons. Adventitial fibroblasts (AFs), a subtype of mesenchymal stromal cell, are the dominant constituents in adventitial spaces, regulating vascular integrity while organizing the accumulation and activation of a variety of interacting immune cells. In contrast, pericytes are stromal mural cells that support microvascular capillaries and surround organ-specific parenchymal cells. Here, we outline the unique immune and non-immune composition of perivascular tissue immune niches, with an emphasis on the heterogeneity and immunoregulatory functions of AFs and pericytes across diverse organs. We will discuss how perivascular stromal cells contribute to the regulation of innate and adaptive immune responses and integrate immunological signals to impact tissue health and disease.

Risk Factors for High-Grade Meningioma in Brain and Spine: Systematic Review and Meta-analysis

BACKGROUND

Histologic grade has important implications for the management in meningioma. It is important to understand the risk of high-grade meningioma (grades II and III). In this article, we systematically reviewed the histologic grade of meningioma depending on the location and sex and its relationship with recurrence.

METHODS

The PubMed and Embase databases were systematically searched until February 4, 2020. We included studies that were not restricted to specific anatomic locations, histologic grade, or the sizes of the tumors. The proportion of high-grade meningiomas depending on the location and sex and the odds ratio (OR) of recurrence were pooled using a random-effects model.

RESULTS

Outcome data were analyzed for 20,336 tumors from 34 studies. We found different proportions of high-grade meningiomas in the brain (12.8%) (95% confidence interval [CI], 10.5%-15.1%) versus the spine (2.4%) (95% CI, 1.0%-3.7%) (P < 0.01). Skull base meningiomas (8.7%) (95% CI, 5.8%-11.6%) had a lower proportion of high-grade meningiomas than non-skull base meningiomas (16.5%) (95% CI, 11.9%-21.1%) (P < 0.01). In addition, high-grade meningiomas were more likely to occur in male patients (18.0%) (95% CI, 10.1%-25.9%) than female patients (7.0%) (95% CI, 3.5%-10.6%) (P = 0.01). Higher rates of recurrence (OR = 13.83) were confirmed for high-grade meningiomas than grade I meningiomas (95% CI, 4.10-46.65) (P < 0.01).

CONCLUSIONS

This meta-analysis found that intracranial, nonskull base, and male sex are risk factors for high-grade meningioma, and high-grade meningioma had a much higher recurrence rate as compared with grade I meningioma.

Central Nervous System Fibroblast-Like Cells in Stroke and Other Neurological Disorders

Fibroblasts are the most common cell type of connective tissues. In the central nervous system (CNS), fibroblast-like cells are mainly located in the meninges and perivascular Virchow-Robin space. The origins of these fibroblast-like cells and their functions in both CNS development and pathological conditions remain largely unknown. In this review, we first introduce the anatomic location and molecular markers of CNS fibroblast-like cells. Next, the functions of fibroblast-like cells in CNS development and neurological disorders, including stroke, CNS traumatic injuries, and other neurological diseases, are discussed. Third, current challenges and future directions in the field are summarized. We hope to provide a synthetic review that stimulates future research on CNS fibroblast-like cells.