Subcommissural organ, cerebrospinal fluid circulation, and hydrocephalus

Congenital hydrocephalus: a review of recent advances in genetic etiology and molecular mechanisms

The global prevalence rate for congenital hydrocephalus (CH) is approximately one out of every five hundred births with multifaceted predisposing factors at play. Genetic influences stand as a major contributor to CH pathogenesis, and epidemiological evidence suggests their involvement in up to 40% of all cases observed globally. Knowledge about an individual's genetic susceptibility can significantly improve prognostic precision while aiding clinical decision-making processes. However, the precise genetic etiology has only been pinpointed in fewer than 5% of human instances. More occurrences of CH cases are required for comprehensive gene sequencing aimed at uncovering additional potential genetic loci. A deeper comprehension of its underlying genetics may offer invaluable insights into the molecular and cellular basis of this brain disorder. This review provides a summary of pertinent genes identified through gene sequencing technologies in humans, in addition to the 4 genes currently associated with CH (two X-linked genes L1CAM and AP1S2, two autosomal recessive MPDZ and CCDC88C). Others predominantly participate in aqueduct abnormalities, ciliary movement, and nervous system development. The prospective CH-related genes revealed through animal model gene-editing techniques are further outlined, focusing mainly on 4 pathways, namely cilia synthesis and movement, ion channels and transportation, Reissner's fiber (RF) synthesis, cell apoptosis, and neurogenesis. Notably, the proper functioning of motile cilia provides significant impulsion for cerebrospinal fluid (CSF) circulation within the brain ventricles while mutations in cilia-related genes constitute a primary cause underlying this condition. So far, only a limited number of CH-associated genes have been identified in humans. The integration of genotype and phenotype for disease diagnosis represents a new trend in the medical field. Animal models provide insights into the pathogenesis of CH and contribute to our understanding of its association with related complications, such as renal cysts, scoliosis, and cardiomyopathy, as these genes may also play a role in the development of these diseases. Genes discovered in animals present potential targets for new treatments but require further validation through future human studies.

The Physiological Occlusion of the Central Canal May Be a Prerequisite for Syringomyelia Formation

OBJECTIVE

Syringomyelia is a common central nervous system disease characterized by the dilation of the central canal (CC). Regarding the pathogenesis of syringomyelia, cerebrospinal fluid (CSF) circulation obstruction in the subarachnoid space (SAS) of the spinal cord has been widely accepted. However, clinical and animal studies on obstructing the CSF in SAS failed to form syringomyelia, challenging the theory of SAS obstruction. The precise pathogenesis remains unknown.

METHODS

We utilized an extradural compression rat model to investigate the pathogenesis underlying syringomyelia. Magnetic resonance imaging enabled detection of syringomyelia formation. To assess CSF flow within the SAS, Evans blue was infused into the cisterna magna. Histological analysis allowed morphological examination of the CC. Furthermore, CSF flow through the CC was traced using Ovalbumin Alexa-Flour 647 conjugate (OAF-647). Scanning electron microscopy (SEM) enabled visualization of ependymal cilia.

RESULTS

The findings showed that the dura mater below the compression segment exhibited lighter coloration relative to the region above the compression, indicative of partial obstruction within the SAS. However, the degree of SAS occlusion did not significantly differ between syringomyelia (SM-Y group) and those without (SM-N group). Intriguingly, hematoxylin and eosin staining and CSF tracing revealed occlusion of the CC accompanied by reduced CSF flow in the SM-Y group compared to SM-N and control groups. SEM images uncovered impairment of ependymal cilia inside the syringomyelia.

CONCLUSION

CC occlusion may represent a physiological prerequisite for syringomyelia formation, while SAS obstruction serves to initiate disease onset. The impairment of ependymal cilia appears to facilitate progression of syringomyelia.

Atavistic and vestigial anatomical structures in the head, neck, and spine: an overview

Organisms may retain nonfunctional anatomical features as a consequence of evolutionary natural selection. Resultant atavistic and vestigial anatomical structures have long been a source of perplexity. Atavism is when an ancestral trait reappears after loss through an evolutionary change in previous generations, whereas vestigial structures are remnants that are largely or entirely functionless relative to their original roles. While physicians are cognizant of their existence, atavistic and vestigial structures are rarely emphasized in anatomical curricula and can, therefore, be puzzling when discovered incidentally. In addition, the literature is replete with examples of the terms atavistic and vestigial being used interchangeably without careful distinction between them. We provide an overview of important atavistic and vestigial structures in the head, neck, and spine that can serve as a reference for anatomists and clinical neuroscientists. We review the literature on atavistic and vestigial anatomical structures of the head, neck, and spine that may be encountered in clinical practice. We define atavistic and vestigial structures and employ these definitions consistently when classifying anatomical structures. Pertinent anatomical structures are numerous and include human tails, plica semilunaris, the vomeronasal organ, levator claviculae, and external ear muscles, to name a few. Atavistic and vestigial structures are found throughout the head, neck, and spine. Some, such as human tails and branchial cysts may be clinically symptomatic. Literature reports indicate that their prevalence varies across populations. Knowledge of atavistic and vestigial anatomical structures can inform diagnoses, prevent misrecognition of variation for pathology, and guide clinical interventions.

A novel feature of the ancient organ: A possible involvement of the subcommissural organ in neurogenic/gliogenic potential in the adult brain

The subcommissural organ (SCO) is a circumventricular organ highly conserved in vertebrates from Cyclostomata such as lamprey to mammals including human. The SCO locates in the boundary between the third ventricle and the entrance of the aqueduct of Sylvius. The SCO functions as a secretory organ producing a variety of proteins such as SCO-spondin, transthyretin, and basic fibroblast growth factor (FGF) into the cerebrospinal fluid (CSF). A significant contribution of the SCO has been thought to maintain the homeostasis of CSF dynamics. However, evidence has shown a possible role of SCO on neurogenesis in the adult brain. This review highlights specific features of the SCO related to adult neurogenesis, suggested by the progress of understanding SCO functions. We begin with a brief history of the SCO discovery and continue to structural features, gene expression, and a possible role in adult neurogenesis suggested by the SCO transplant experiment.

Early Regressive Development of the Subcommissural Organ of Two Human Fetuses with Non-Communicating Hydrocephalus

Hydrocephalus is a central nervous system condition characterized by CSF buildup and ventricular hypertrophy. It is divided into two types: communicative and non-communicating hydrocephalus. Congenital hydrocephalus has been linked to several changes in the subcommissural organ (SCO). However, it is unclear whether these changes occur before or as a result of the hydrocephalic illness. This report presents three cases of human fetuses with hydrocephalus: one non-communicating case, two communicating cases, and two controls. Hematoxylin-Eosin (H&E) or cresyl violet and immunohistochemistry with anti-transthyretin were used to analyze SCO morphological and secretory changes. We conclude that in the cases presented here, there could be an early regression in the SCO of the communicating cases that is not present in the non-communicating case.

Ptpn20 deletion in H-Tx rats enhances phosphorylation of the NKCC1 cotransporter in the choroid plexus: an evidence of genetic risk for hydrocephalus in an experimental study

BACKGROUND

Congenital hydrocephalus occurs with some inheritable characteristics, but the mechanisms of its development remain poorly understood. Animal models provide the opportunity to identify potential genetic causes in this condition. The Hydrocephalus-Texas (H-Tx) rat strain is one of the most studied animal models for investigating the causative genetic alterations and analyzing downstream pathogenetic mechanisms of congenital hydrocephalus.

METHODS

Comparative genomic hybridization (CGH) array on non-hydrocephalic and hydrocephalic H-Tx rats was used to identify causative genes of hydrocephalus. Targeted gene knockout mice were generated by CRISPR/Cas9 to study the role of this gene in hydrocephalus.

RESULTS

CGH array revealed a copy number loss in chromosome 16p16 region in hydrocephalic H-Tx rats at 18 days gestation, encompassing the protein tyrosine phosphatase non-receptor type 20 (Ptpn20), a non-receptor tyrosine phosphatase, without change in most non-hydrocephalic H-Tx rats. Ptpn20-knockout (Ptpn20-/-) mice were generated and found to develop ventriculomegaly at 8 weeks. Furthermore, high expression of phosphorylated Na-K-Cl cotransporter 1 (pNKCC1) was identified in the choroid plexus (CP) epithelium of mice lacking Ptpn20 from 8 weeks until 72 weeks.

CONCLUSIONS

This study determined the chromosomal location of the hydrocephalus-associated Ptpn20 gene in hydrocephalic H-Tx rats. The high level of pNKCC1 mediated by Ptpn20 deletion in CP epithelium may cause overproduction of cerebrospinal fluid and contribute to the formation of hydrocephalus in Ptpn20-/- mice. Ptpn20 may be a potential therapeutic target in the treatment of hydrocephalus.

The subcommissural organ maintains features of neuroepithelial cells in the adult mouse

The subcommissural organ (SCO) is a part of the circumventricular organs located in the dorsocaudal region of the third ventricle at the entrance of the aqueduct of Sylvius. The SCO comprises epithelial cells and produces high molecular weight glycoproteins, which are secreted into the third ventricle and become part of Reissner's fibre in the cerebrospinal fluid. Abnormal development of the SCO has been linked with congenital hydrocephalus, a condition characterized by excessive accumulation of cerebrospinal fluid in the brain. In the present study, we characterized the SCO cells in the adult mouse brain to gain insights into the possible role of this brain region. Immunohistochemical analyses revealed that expression of Pax6, a transcription factor essential for SCO differentiation during embryogenesis, is maintained in the SCO at postnatal stages from P0 to P84. SCO cells in the adult brain expressed known neural stem/progenitor cell (NSPC) markers, Sox2 and vimentin. The adult SCO cells also expressed proliferating marker PCNA, although expression of another proliferation marker Ki67, indicating a G₂/M phase, was not detected. The SCO cells did not incorporate BrdU, a marker for DNA synthesis in the S phase. Therefore, the SCO cells have a potential for proliferation but are quiescent for cell division in the adult. The SCO cells also expressed GFAP, a marker for astrocytes or NSPCs, but not NeuN (for neurons). A few cells positive for Iba1 (microglia), Olig2 (for oligodendrocytes) and PDGFRα (oligodendrocyte progenitors) existed within or on the periphery of the SCO. These findings revealed that the SCO cells have a unique feature as secretory yet immature neuroepithelial cells in the adult mouse brain.

Genetics and Molecular Pathogenesis of Human Hydrocephalus

Hydrocephalus is a neurological disorder with an incidence of 80-125 per 100,000 live births in the United States. The molecular pathogenesis of this multidimensional disorder is complex and has both genetic and environmental influences. This review aims to discuss the genetic and molecular alterations described in human hydrocephalus, from well-characterized, heritable forms of hydrocephalus (e.g., X-linked hydrocephalus from L1CAM variants) to those affecting cilia motility and other complex pathologies such as neural tube defects and Dandy-Walker syndrome. Ventricular zone disruption is one key pattern among congenital and acquired forms of hydrocephalus, with abnormalities in cadherins, which mediate neuroepithelium/ependymal cell junctions and contribute to the pathogenesis and severity of the disease. Given the relationship between hydrocephalus pathogenesis and neurodevelopment, future research should elucidate the genetic and molecular mechanisms that regulate ventricular zone integrity and stem cell biology.

SCO-spondin, a giant matricellular protein that regulates cerebrospinal fluid activity

Cerebrospinal fluid is a clear fluid that occupies the ventricular and subarachnoid spaces within and around the brain and spinal cord. Cerebrospinal fluid is a dynamic signaling milieu that transports nutrients, waste materials and neuroactive substances that are crucial for the development, homeostasis and functionality of the central nervous system. The mechanisms that enable cerebrospinal fluid to simultaneously exert these homeostatic/dynamic functions are not fully understood. SCO-spondin is a large glycoprotein secreted since the early stages of development into the cerebrospinal fluid. Its domain architecture resembles a combination of a matricellular protein and the ligand-binding region of LDL receptor family. The matricellular proteins are a group of extracellular proteins with the capacity to interact with different molecules, such as growth factors, cytokines and cellular receptors; enabling the integration of information to modulate various physiological and pathological processes. In the same way, the LDL receptor family interacts with many ligands, including β-amyloid peptide and different growth factors. The domains similarity suggests that SCO-spondin is a matricellular protein enabled to bind, modulate, and transport different cerebrospinal fluid molecules. SCO-spondin can be found soluble or polymerized into a dynamic threadlike structure called the Reissner fiber, which extends from the diencephalon to the caudal tip of the spinal cord. Reissner fiber continuously moves caudally as new SCO-spondin molecules are added at the cephalic end and are disaggregated at the caudal end. This movement, like a conveyor belt, allows the transport of the bound molecules, thereby increasing their lifespan and action radius. The binding of SCO-spondin to some relevant molecules has already been reported; however, in this review we suggest more than 30 possible binding partners, including peptide β-amyloid and several growth factors. This new perspective characterizes SCO-spondin as a regulator of cerebrospinal fluid activity, explaining its high evolutionary conservation, its apparent multifunctionality, and the lethality or severe malformations, such as hydrocephalus and curved body axis, of knockout embryos. Understanding the regulation and identifying binding partners of SCO-spondin are crucial for better comprehension of cerebrospinal fluid physiology.

The Enigmatic Reissner's Fiber and the Origin of Chordates

Reissner’s fiber (RF) is a secreted filament that floats in the neural canal of chordates. Since its discovery in 1860, there has been no agreement on its primary function, and its strong conservation across chordate species has remained a mystery for comparative neuroanatomists. Several findings, including the chemical composition and the phylogenetic history of RF, clinical observations associating RF with the development of the neural canal, and more recent studies suggesting that RF is needed to develop a straight vertebral column, may shed light on the functions of this structure across chordates. In this article, we will briefly review the evidence mentioned above to suggest a role of RF in the origin of fundamental innovations of the chordate body plan, especially the elongation of the neural tube and maintenance of the body axis. We will also mention the relevance of RF for medical conditions like hydrocephalus, scoliosis of the vertebral spine and possibly regeneration of the spinal cord.

Hydrocephalus in mouse B3glct mutants is likely caused by defects in multiple B3GLCT substrates in ependymal cells and subcommissural organ

Peters plus syndrome, characterized by defects in eye and skeletal development with isolated cases of ventriculomegaly/hydrocephalus, is caused by mutations in the β3-glucosyltransferase (B3GLCT) gene. In the endoplasmic reticulum, B3GLCT adds glucose to O-linked fucose on properly folded Thrombospondin Type 1 Repeats (TSRs). The resulting glucose-fucose disaccharide is proposed to stabilize the TSR fold and promote secretion of B3GLCT substrates, with some substrates more sensitive than others to loss of glucose. Mouse B3glct mutants develop hydrocephalus at high frequency. In this study, we demonstrated that B3glct mutant ependymal cells had fewer cilia basal bodies and altered translational polarity compared to controls. Localization of mRNA encoding A Disintegrin and Metalloproteinase with ThromboSpondin type 1 repeat 20 (ADAMTS20) and ADAMTS9, suggested that reduced function of these B3GLCT substrates contributed to ependymal cell abnormalities. In addition, we showed that multiple B3GLCT substrates (Adamts3, Adamts9, and Adamts20) are expressed by the subcommissural organ, that subcommissural organ-spondin (SSPO) TSRs were modified with O-linked glucose-fucose, and that loss of B3GLCT reduced secretion of SSPO in cultured cells. In the B3glct mutant subcommissural organ intracellular SSPO levels were reduced and BiP levels increased, suggesting a folding defect. Secreted SSPO colocalized with BiP, raising the possibility that abnormal extracellular assembly of SSPO into Reissner's fiber also contributed to impaired CSF flow in mutants. Combined, these studies underscore the complexity of the B3glct mutant hydrocephalus phenotype and demonstrate that impaired cerebrospinal fluid (CSF) flow likely stems from the collective effects of the mutation on multiple processes.

Camel regulates development of the brain ventricular system

Development of the brain ventricular system of vertebrates and the molecular mechanisms involved are not fully understood. The developmental genes expressed in the elements of the brain ventricular system such as the ependyma and circumventricular organs act as molecular determinants of cell adhesion critical for the formation of brain ventricular system. They control brain development and function, including the flow of cerebrospinal fluid. Here, we describe the novel distantly related member of the zebrafish L1-CAM family of genes-camel. Whereas its maternal transcripts distributed uniformly, the zygotic transcripts demonstrate clearly defined expression patterns, in particular in the axial structures: floor plate, hypochord, and roof plate. camel expresses in several other cell lineages with access to the brain ventricular system, including the midbrain roof plate, subcommissural organ, organum vasculosum lamina terminalis, median eminence, paraventricular organ, flexural organ, and inter-rhombomeric boundaries. This expression pattern suggests a role of Camel in neural development. Several isoforms of Camel generated by differential splicing of exons encoding the sixth fibronectin type III domain enhance cell adhesion differentially. The antisense oligomer morpholino-mediated loss-of-function of Camel affects cell adhesion and causes hydrocephalus and scoliosis manifested via the tail curled down phenotype. The subcommissural organ's derivative-the Reissner fiber-participates in the flow of cerebrospinal fluid. The Reissner fiber fails to form upon morpholino-mediated Camel loss-of-function. The Camel mRNA-mediated gain-of-function causes the Reissner fiber misdirection. This study revealed a link between Chl1a/Camel and Reissner fiber formation, and this supports the idea that CHL1 is one of the scoliosis factors.

Evidence for the involvement of caspases in establishing proper cerebrospinal fluid hydrodynamics

A large number of cells undergo apoptosis via caspase activation during and after neural tube closure (NTC) in mammals. Apoptosis is executed by either intrinsic or extrinsic apoptotic pathways, and inhibition of each pathway causes developmental defects around NTC stages, which hampers the physiological roles of apoptosis and caspases after NTC. We generated transgenic mice in which a broad spectrum of caspases could be suppressed in a spatiotemporal manner by pan-caspase inhibitor protein p35 originating from baculovirus. Mice with nervous system-specific expression of p35 (Nestin-Cre (NCre);p35V mice) exhibited postnatal lethality within 1 month after birth. They were born at the expected Mendelian ratio, but demonstrated severe postnatal growth retardation and hydrocephalus. The flow of cerebrospinal fluid (CSF) between the third and fourth ventricles was disturbed, whereas neither stenosis nor abnormality in ciliary morphology was observed in the pathway of CSF flow. Hydrocephalus and growth retardation of NCre;p35V mice were not rescued by the deletion of RIPK3, an essential factor for necroptosis which occurs in the absence of caspase-8 activation during development. The CSF of NCre;p35V mice contained a larger amount of secreted proteins than that of the controls. These findings suggest that the establishment of proper CSF dynamics requires caspase activity during brain development after NTC.

A novel hypomorphic allele of Spag17 causes primary ciliary dyskinesia phenotypes in mice

Primary ciliary dyskinesia (PCD) is a human condition of dysfunctional motile cilia characterized by recurrent lung infection, infertility, organ laterality defects and partially penetrant hydrocephalus. We recovered a mouse mutant from a forward genetic screen that developed many of the hallmark phenotypes of PCD. Whole-exome sequencing identified this primary ciliary dyskinesia only (Pcdo) allele to be a nonsense mutation (c.5236A>T) in the Spag17 coding sequence creating a premature stop codon (K1746*). The Pcdo variant abolished several isoforms of SPAG17 in the Pcdo mutant testis but not in the brain. Our data indicate differential requirements for SPAG17 in different types of motile cilia. SPAG17 is essential for proper development of the sperm flagellum and is required for either development or stability of the C1 microtubule structure within the central pair apparatus of the respiratory motile cilia, but not the brain ependymal cilia. We identified changes in ependymal ciliary beating frequency, but these did not appear to alter lateral ventricle cerebrospinal fluid flow. Aqueductal stenosis resulted in significantly slower and abnormally directed cerebrospinal fluid flow, and we suggest that this is the root cause of the hydrocephalus. The Spag17Pcdo homozygous mutant mice are generally viable to adulthood but have a significantly shortened lifespan, with chronic morbidity. Our data indicate that the c.5236A>T Pcdo variant is a hypomorphic allele of Spag17 that causes phenotypes related to motile, but not primary, cilia. Spag17Pcdo is a useful new model for elucidating the molecular mechanisms underlying central pair PCD pathogenesis in the mouse.This article has an associated First Person interview with the first author of the paper.

The role of lipids in ependymal development and the modulation of adult neural stem cell function during aging and disease

Within the adult mammalian central nervous system, the ventricular-subventricular zone (V-SVZ) lining the lateral ventricles houses neural stem cells (NSCs) that continue to produce neurons throughout life. Developmentally, the V-SVZ neurogenic niche arises during corticogenesis following the terminal differentiation of telencephalic radial glial cells (RGCs) into either adult neural stem cells (aNSCs) or ependymal cells. In mice, these two cellular populations form rosettes during the late embryonic and early postnatal period, with ependymal cells surrounding aNSCs. These aNSCs and ependymal cells serve a number of key purposes, including the generation of neurons throughout life (aNSCs), and acting as a barrier between the CSF and the parenchyma and promoting CSF bulk flow (ependymal cells). Interestingly, the development of this neurogenic niche, as well as its ongoing function, has been shown to be reliant on different aspects of lipid biology. In this review we discuss the developmental origins of the rodent V-SVZ neurogenic niche, and highlight research which has implicated a role for lipids in the physiology of this part of the brain. We also discuss the role of lipids in the maintenance of the V-SVZ niche, and discuss new research which has suggested that alterations to lipid biology could contribute to ependymal cell dysfunction in aging and disease.

The Interstitial System of the Brain in Health and Disease

The brain interstitial fluid (ISF) and the cerebrospinal fluid (CSF) cushion and support the brain cells. The ISF occupies the brain interstitial system (ISS), whereas the CSF fills the brain ventricles and the subarachnoid space. The brain ISS is an asymmetrical, tortuous, and exceptionally confined space between neural cells and the brain microvasculature. Recently, with a newly developed in vivo measuring technique, a series of discoveries have been made in the brain ISS and the drainage of ISF. The goal of this review is to confer recent advances in our understanding of the brain ISS, including its structure, function, and the various processes mediating or disrupting ISF drainage in physiological and pathological conditions. The brain ISF in the deep brain regions has recently been demonstrated to drain in a compartmentalized ISS instead of a highly connected system, together with the drainage of ISF into the cerebrospinal fluid (CSF) at the surface of the cerebral cortex and the transportation from CSF into cervical lymph nodes. Besides, accumulation of tau in the brain ISS in conditions such as Alzheimer’s disease and its link to the sleep-wake cycle and sleep deprivation, clearance of ISF in a deep sleep via increased CSF flow, novel approaches to remove beta-amyloid from the brain ISS, and obstruction to the ISF drainage in neurological conditions are deliberated. Moreover, the role of ISS in the passage of extracellular vesicles (EVs) released from neural cells and the rapid targeting of therapeutic EVs into neural cells in the entire brain following an intranasal administration, and the promise and limitations of ISS based drug delivery approaches are discussed

Functional loss of Ccdc151 leads to hydrocephalus in a mouse model of primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder affecting normal structure and function of motile cilia, phenotypically manifested as chronic respiratory infections, laterality defects and infertility. Autosomal recessive mutations in genes encoding for different components of the ciliary axoneme have been associated with PCD in humans and in model organisms. The CCDC151 gene encodes for a coiled-coil axonemal protein that ensures correct attachment of outer dynein arm (ODA) complexes to microtubules. A correct arrangement of dynein arm complexes is required to provide the proper mechanical force necessary for cilia beat. Loss-of-function mutations in CCDC151 in humans leads to PCD disease with respiratory distress and defective left-right body asymmetry. In mice with the Ccdc151Snbl loss-of-function mutation (Snowball mutant), left-right body asymmetry with heart defects have been observed. Here, we demonstrate that loss of Ccdc151 gene function via targeted gene deletion in mice leads to perinatal lethality and congenital hydrocephalus. Microcomputed tomography (microCT) X-ray imaging of Ccdc151-β-galactosidase reporter expression in whole-mount brain and histological analysis show that Ccdc151 is expressed in ependymal cells lining the ventricular brain system, further confirming the role of Ccdc151 dysfunction in hydrocephalus development. Analyzing the features of hydrocephalus in the Ccdc151-knockout animals by microCT volumetric imaging, we observe continuity of the aqueduct of Sylvius, indicating the communicating nature of hydrocephalus in the Ccdc151-knockout animals. Congenital defects in left-right asymmetry and male infertility have been also observed in Ccdc151-null animals. Ccdc151 gene deletion in adult animals results in abnormal sperm counts and defective sperm motility.This article has an associated First Person interview with the joint first authors of the paper.

Strain-specific differences in brain gene expression in a hydrocephalic mouse model with motile cilia dysfunction

Congenital hydrocephalus results from cerebrospinal fluid accumulation in the ventricles of the brain and causes severe neurological damage, but the underlying causes are not well understood. It is associated with several syndromes, including primary ciliary dyskinesia (PCD), which is caused by dysfunction of motile cilia. We previously demonstrated that mouse models of PCD lacking ciliary proteins CFAP221, CFAP54 and SPEF2 all have hydrocephalus with a strain-dependent severity. While morphological defects are more severe on the C57BL/6J (B6) background than 129S6/SvEvTac (129), cerebrospinal fluid flow is perturbed on both backgrounds, suggesting that abnormal cilia-driven flow is not the only factor underlying the hydrocephalus phenotype. Here, we performed a microarray analysis on brains from wild type and nm1054 mice lacking CFAP221 on the B6 and 129 backgrounds. Expression differences were observed for a number of genes that cluster into distinct groups based on expression pattern and biological function, many of them implicated in cellular and biochemical processes essential for proper brain development. These include genes known to be functionally relevant to congenital hydrocephalus, as well as formation and function of both motile and sensory cilia. Identification of these genes provides important clues to mechanisms underlying congenital hydrocephalus severity.

A historical approach to the ventricular system of the brain

Introducción. El sistema ventricular encefálico se conoció, con parcialidad, en el siglo III a.C., fecha desde la que diversos investigadores contribuyeron a una mejor comprensión de dicho sistema, desentrañando sus ubicaciones en el sistema nervioso central y relacionándolos con ciertos aspectos funcionales que surgieron de conceptos filosóficos. Esto permitió un acercamiento más objetivo hacia las cavitaciones relacionadas con la formación de líquido cerebroespinal.Objetivo. Referenciar, de forma cronológica, los conceptos más trascendentes de la historia del sistema ventricular encefálico.Materiales y métodos. Se consultaron diversas fuentes bibliográficas relacionadas con el sistema ventricular, para después ordenarlas según su cronología, de modo que se concluyera con una aproximación más concreta de la morfología funcional del sistema ventricular.Conclusión. Aristóteles fue el primero en abordar el sistema ventricular encefálico, de modo que, conforme el paso de los años, su conocimiento se fue depurando en cuanto a organización, función y número de cavidades, hasta llegar a proponer la existencia de ocho ventrículos. En la actualidad se reconocen cinco ventrículos, de los cuales cuatro son componentes encefálicos: dos en cerebro, uno en diencéfalo, otro en tronco encefálico y un quinto en la parte terminal de la médula espinal.

Yap is required for ependymal integrity and is suppressed in LPA-induced hydrocephalus

Timely generation and normal maturation of ependymal cells along the aqueduct are critical for preventing physical blockage between the third and fourth ventricles and the development of fetal non-communicating hydrocephalus. Our study identifies Yap, the downstream effector of the evolutionarily conserved Hippo pathway, as a central regulator for generating developmentally controlled ependymal cells along the ventricular lining of the aqueduct. Yap function is necessary for proper proliferation of progenitors and apical attachment of ependymal precursor cells. Importantly, an injury signal initiated by lysophosphatidic acid (LPA), an upstream regulator of Yap that can cause fetal haemorrhagic hydrocephalus, deregulates Yap in the developing aqueduct. LPA exposure leads to the loss of N-cadherin concentrations at the apical endfeet, which can be partially restored by forced Yap expression and more efficiently by phosphomimetic Yap. These results reveal a novel function of Yap in retaining tissue junctions during normal development and after fetal brain injury.

In Vivo Expression of the PTB-deleted Odin Mutant Results in Hydrocephalus

Odin has been implicated in the downstream signaling pathway of receptor tyrosine kinases, such as the epidermal growth factor and Eph receptors. However, the physiologically relevant function of Odin needs to be further determined. In this study, we used Odin heterozygous mice to analyze the Odin expression pattern; the targeted allele contained a β-geo gene trap vector inserted into the 14th intron of the Odin gene. Interestingly, we found that Odin was exclusively expressed in ependymal cells along the brain ventricles. In particular, Odin was highly expressed in the subcommissural organ, a small ependymal glandular tissue. However, we did not observe any morphological abnormalities in the brain ventricles or ependymal cells of Odin null-mutant mice. We also generated BAC transgenic mice that expressed the PTB-deleted Odin (dPTB) after a floxed GFP-STOP cassette was excised by tissue-specific Cre expression. Strikingly, Odin-dPTB expression played a causative role in the development of the hydrocephalic phenotype, primarily in the midbrain. In addition, Odin-dPTB expression disrupted proper development of the subcommissural organ and interfered with ependymal cell maturation in the cerebral aqueduct. Taken together, our findings strongly suggest that Odin plays a role in the differentiation of ependymal cells during early postnatal brain development.

Camk2a-Cre-mediated conditional deletion of chromatin remodeler Brg1 causes perinatal hydrocephalus

Mammalian SWI/SNF-like BAF chromatin remodeling complexes are essential for many aspects of neural development. Mutations in the genes encoding the core subunit Brg1/SmarcA4 or other complex components cause neurodevelopmental diseases and are associated with autism. Congenital hydrocephalus is a serious brain disorder often experienced by these patients. We report a role of Brg1 in the pathogenesis of hydrocephalus disorder. We discovered an unexpected early activity of mouse Camk2a-Cre transgene, which mediates Brg1 deletion in a subset of forebrain neurons beginning in the late embryonic stage. Brg1 deletion in these neurons led to severe congenital hydrocephalus with enlargement of the lateral ventricles and attenuation of the cerebral cortex. The Brg1-deficient mice had significantly smaller subcommissural organs and narrower Sylvian aqueducts than mice that express normal levels of Brg1. Effects were non-cell autonomous and may be responsible for the development of the congenital hydrocephalus phenotype. Our study provides evidence indicating that abnormalities in Brg1 function result in defects associated with neurodevelopmental disorders and autism.

Concomitant inactivation of foxo3a and fancc or fancd2 reveals a two-tier protection from oxidative stress-induced hydrocephalus

AIMS

This study seeks at investigating the cause of hydrocephalus, and at identifying therapeutic targets for the prevention of hydrocephalus.

RESULTS

In this study, we show that inactivation of the Foxo3a gene in two mouse models of Fanconi anemia (FA) leads to the development of hydrocephalus in late embryonic stage and after birth. More than 50% of Foxo3a(-/-) Fancc(-/-) or Foxo3a(-/-) Fancd2(-/-) mice die during embryonic development or within 6 months of life as a result of hydrocephalus characterized by cranial distortion, dilation of the ventricular system, reduced thickness of the cerebral cortex, and disorganization of the ependymal cilia and subcommissural organ. Combined deficiency of Foxo3a and Fancc or Fancd2 not only impairs the self-renewal capacity but also markedly increases the apoptosis of neural stem and progenitor cells (NSPCs), leading to defective neurogenesis. Increased accumulation of reactive oxygen species (ROS) and subsequently de-regulated mitosis and ultimately apoptosis in the neural stem or progenitor cells is identified as one of the potential mechanisms of congenital obstructive hydrocephalus.

INNOVATION

The work unravels a two-tier protective mechanism for preventing oxidative stress-induced hydrocephalus.

CONCLUSION

The deletion of Foxo3a in FA mice increased the accumulation of ROS and subsequently de-regulated mitosis and ultimately apoptosis in the NSPCs, leading to hydrocephalus development.

Strain-dependent brain defects in mouse models of primary ciliary dyskinesia with mutations in Pcdp1 and Spef2

Hydrocephalus is caused by the accumulation of cerebrospinal fluid (CSF) in the cerebral ventricular system which results in an enlargement of the cranium due to increased intraventricular pressure. The increase in pressure within the brain typically results in sloughing of ciliated ependymal cells, loss of cortical gray matter, and increased gliosis. Congenital hydrocephalus is associated with several syndromes including primary ciliary dyskinesia (PCD), a rare, genetically heterogeneous, pediatric syndrome that results from defects in motile cilia and flagella. We have examined the morphological and physiological defects in the brains of two mouse models of PCD, nm1054 and bgh, which have mutations in Pcdp1 (also known as Cfap221) and Spef2, respectively. Histopathological and immunohistochemical analyses of mice with these mutations on the C57BL/6J and 129S6/SvEvTac genetic backgrounds demonstrate strain-dependent morphological brain damage. Alterations in astrocytosis, microglial activation, myelination, and the neuronal population were identified and are generally more severe on the C57BL/6J background. Analysis of ependymal ciliary clearance ex vivo and CSF flow in vivo demonstrate a physiological defect in nm1054 and bgh mice on both genetic backgrounds, indicating that abnormal cilia-driven flow is not the sole determinant of the severity of hydrocephalus in these models. These results suggest that genetic modifiers play an important role in susceptibility to severe PCD-associated hydrocephalus.

Structure and function of the ependymal barrier and diseases associated with ependyma disruption

The neuroepithelium is a germinal epithelium containing progenitor cells that produce almost all of the central nervous system cells, including the ependyma. The neuroepithelium and ependyma constitute barriers containing polarized cells covering the embryonic or mature brain ventricles, respectively; therefore, they separate the cerebrospinal fluid that fills cavities from the developing or mature brain parenchyma. As barriers, the neuroepithelium and ependyma play key roles in the central nervous system development processes and physiology. These roles depend on mechanisms related to cell polarity, sensory primary cilia, motile cilia, tight junctions, adherens junctions and gap junctions, machinery for endocytosis and molecule secretion, and water channels. Here, the role of both barriers related to the development of diseases, such as neural tube defects, ciliary dyskinesia, and hydrocephalus, is reviewed.

Distribution of MT1 melatonin receptor promoter-driven RFP expression in the brains of BAC C3H/HeN transgenic mice

The pineal hormone melatonin activates two G-protein coupled receptors (MT1 and MT2) to regulate in part biological functions. The MT1 and MT2 melatonin receptors are heterogeneously distributed in the mammalian brain including humans. In the mouse, only a few reports have assessed the expression of the MT1 melatonin receptor expression using 2-iodomelatonin binding, in situ hybridization and/or polymerase chain reaction (PCR). Here, we described a transgenic mouse in which red fluorescence protein (RFP) is expressed under the control of the endogenous MT1 promoter, by inserting RFP cDNA at the start codon of MTNR1a gene within a bacterial artificial chromosome (BAC) and expressing this construct as a transgene. The expression of RFP in the brain of this mouse was examined either directly under a fluorescent microscope or immunohistochemically using an antibody against RFP (RFP-MT1). RFP-MT1 expression was observed in many brain regions including the subcommissural organ, parts of the ependyma lining the lateral and third ventricles, the aqueduct, the hippocampus, the cerebellum, the pars tuberalis, the habenula and the habenula commissure. This RFP-MT1 transgenic model provides a unique tool for studying the distribution of the MT1 receptor in the brain of mice, its cell-specific expression and its function in vivo.

Genetic deletion of afadin causes hydrocephalus by destruction of adherens junctions in radial glial and ependymal cells in the midbrain

Adherens junctions (AJs) play a role in mechanically connecting adjacent cells to maintain tissue structure, particularly in epithelial cells. The major cell–cell adhesion molecules at AJs are cadherins and nectins. Afadin binds to both nectins and α-catenin and recruits the cadherin-β-catenin complex to the nectin-based cell–cell adhesion site to form AJs. To explore the role of afadin in radial glial and ependymal cells in the brain, we generated mice carrying a nestin-Cre-mediated conditional knockout (cKO) of the afadin gene. Newborn afadin-cKO mice developed hydrocephalus and died neonatally. The afadin-cKO brain displayed enlarged lateral ventricles and cerebral aqueduct, resulting from stenosis of the caudal end of the cerebral aqueduct and obliteration of the ventral part of the third ventricle. Afadin deficiency further caused the loss of ependymal cells from the ventricular and aqueductal surfaces. During development, radial glial cells, which terminally differentiate into ependymal cells, scattered from the ventricular zone and were replaced by neurons that eventually covered the ventricular and aqueductal surfaces of the afadin-cKO midbrain. Moreover, the denuded ependymal cells were only occasionally observed in the third ventricle and the cerebral aqueduct of the afadin-cKO midbrain. Afadin was co-localized with nectin-1 and N-cadherin at AJs of radial glial and ependymal cells in the control midbrain, but these proteins were not concentrated at AJs in the afadin-cKO midbrain. Thus, the defects in the afadin-cKO midbrain most likely resulted from the destruction of AJs, because AJs in the midbrain were already established before afadin was genetically deleted. These results indicate that afadin is essential for the maintenance of AJs in radial glial and ependymal cells in the midbrain and is required for normal morphogenesis of the cerebral aqueduct and ventral third ventricle in the midbrain.

Ciliogenesis and cerebrospinal fluid flow in the developing Xenopus brain are regulated by foxj1

Background

Circulation of cerebrospinal fluid (CSF) through the ventricular system is driven by motile cilia on ependymal cells of the brain. Disturbed ciliary motility induces the formation of hydrocephalus, a pathological accumulation of CSF resulting in ventricle dilatation and increased intracranial pressure. The mechanism by which loss of motile cilia causes hydrocephalus has not been elucidated. The aim of this study was: (1) to provide a detailed account of the development of ciliation in the brain of the African clawed frog Xenopus laevis; and (2) to analyze the relevance of ependymal cilia motility for CSF circulation and brain ventricle morphogenesis in Xenopus.

Methods

Gene expression analysis of foxj1, the bona fide marker for motile cilia, was used to identify potentially ciliated regions in the developing central nervous system (CNS) of the tadpole. Scanning electron microscopy (SEM) was used to reveal the distribution of mono- and multiciliated cells during successive stages of brain morphogenesis, which was functionally assessed by bead injection and video microscopy of ventricular CSF flow. An antisense morpholino oligonucleotide (MO)-mediated gene knock-down that targeted foxj1 in the CNS was applied to assess the role of motile cilia in the ventricles.

Results

RNA transcripts of foxj1 in the CNS were found from neurula stages onwards. Following neural tube closure, foxj1 expression was seen in distinct ventricular regions such as the zona limitans intrathalamica (ZLI), subcommissural organ (SCO), floor plate, choroid plexus (CP), and rhombomere boundaries. In all areas, expression of foxj1 preceded the outgrowth of monocilia and the subsequent switch to multiciliated ependymal cells. Cilia were absent in foxj1 morphants, causing impaired CSF flow and fourth ventricle hydrocephalus in tadpole-stage embryos.

Conclusions

Motile ependymal cilia are important organelles in the Xenopus CNS, as they are essential for the circulation of CSF and maintenance of homeostatic fluid pressure. The Xenopus CNS ventricles might serve as a novel model system for the analysis of human ciliary genes whose deficiency cause hydrocephalus.

Riding the wave of ependymal cilia: genetic susceptibility to hydrocephalus in primary ciliary dyskinesia

Congenital hydrocephalus is a relatively common and debilitating birth defect with several known physiological causes. Dysfunction of motile cilia on the ependymal cells that line the ventricular surface of the brain can result in hydrocephalus by hindering the proper flow of cerebrospinal fluid. As a result, hydrocephalus can be associated with primary ciliary dyskinesia, a rare pediatric syndrome resulting from defects in ciliary and flagellar motility. Although the prevalence of hydrocephalus in primary ciliary dyskinesia patients is low, it is a common hallmark of the disease in mouse models, suggesting that distinct genetic mechanisms underlie the differences in the development and physiology of human and mouse brains. Mouse models of primary ciliary dyskinesia reveal strain-specific differences in the appearance and severity of hydrocephalus, indicating the presence of genetic modifiers segregating in inbred strains. These models may provide valuable insight into the genetic mechanisms that regulate susceptibility to hydrocephalus under the conditions of ependymal ciliary dysfunction.

Role of the subcommissural organ in the pathogenesis of congenital hydrocephalus in the HTx rat

The present investigation was designed to clarify the role of the subcommissural organ (SCO) in the pathogenesis of hydrocephalus occurring in the HTx rat. The brains of non-affected and hydrocephalic HTx rats from embryonic day 15 (E15) to postnatal day 10 (PN10) were processed for electron microscopy, lectin binding and immunocytochemistry by using a series of antibodies. Cerebrospinal fluid (CSF) samples of non-affected and hydrocephalic HTx rats were collected at PN1, PN7 and PN30 and analysed by one- and two-dimensional electrophoresis, immunoblotting and nanoLC-ESI-MS/MS. A distinct malformation of the SCO is present as early as E15. Since stenosis of the Sylvius aqueduct (SA) occurs at E18 and dilation of the lateral ventricles starts at E19, the malformation of the SCO clearly precedes the onset of hydrocephalus. In the affected rats, the cephalic and caudal thirds of the SCO showed high secretory activity with all methods used, whereas the middle third showed no signs of secretion. At E18, the middle non-secretory third of the SCO progressively fused with the ventral wall of SA, resulting in marked aqueduct stenosis and severe hydrocephalus. The abnormal development of the SCO resulted in the permanent absence of Reissner's fibre (RF) and led to changes in the protein composition of the CSF. Since the SCO is the source of a large mass of sialilated glycoproteins that form the RF and of those that remain CSF-soluble, we hypothesize that the absence of this large mass of negatively charged molecules from the SA domain results in SA stenosis and impairs the bulk flow of CSF through the aqueduct.

Genetic deletion of Rnd3 results in aqueductal stenosis leading to hydrocephalus through up-regulation of Notch signaling

Rho family guanosine triphosphatase (GTPase) 3 (Rnd3), a member of the small Rho GTPase family, is involved in the regulation of cell actin cytoskeleton dynamics, cell migration, and proliferation through the Rho kinase-dependent signaling pathway. We report a role of Rnd3 in the pathogenesis of hydrocephalus disorder. Mice with Rnd3 genetic deletion developed severe obstructive hydrocephalus with enlargement of the lateral and third ventricles, but not of the fourth ventricles. The cerebral aqueducts in Rnd3-null mice were partially or completely blocked by the overgrowth of ependymal epithelia. We examined the molecular mechanism contributing to this Rnd3-deficiency-mediated hydrocephalus and found that Rnd3 is a regulator of Notch signaling. Rnd3 deficiency, through either gene deletion or siRNA knockdown, resulted in a decrease in Notch intracellular domain (NICD) protein degradation. However, there was no correlated change in mRNA change, which in turn led to an increase in NICD protein levels. Immunoprecipitation analysis demonstrated that Rnd3 and NICD physically interacted, and that down-regulation of Rnd3 attenuated NICD protein ubiquitination. This eventually enhanced Notch signaling activity and promoted aberrant growth of aqueduct ependymal cells, resulting in aqueduct stenosis and the development of congenital hydrocephalus. Inhibition of Notch activity rescued the hydrocephalus disorder in the mutant animals.

Structural defects in cilia of the choroid plexus, subfornical organ and ventricular ependyma are associated with ventriculomegaly

Background

Hydrocephalus is a heterogeneous disorder with multiple etiologies that are not yet fully understood. Animal models have implicated dysfunctional cilia of the ependyma and choroid plexus in the development of the disorder. In this report, we sought to determine the origin of the ventriculomegaly in four Bardet Biedl syndrome (BBS) mutant mouse strains as models of a ciliopathy.

Methods

Evans Blue dye was injected into the lateral ventricle of wild- type and BBS mutant mice to determine whether obstruction of intra- or extra-ventricular CSF flow contributed to ventriculomegaly. Transmission electron microscopy (TEM) was used to examine the ultrastructure of the choroid plexus, subfornical organ (SFO), subcommisural organ (SCO), and ventricular ependyma to evaluate their ultrastructure and the morphology of their primary and motile cilia.

Results and discussion

No obstruction of intra- or extra-ventricular CSF flow was observed, implying a communicating form of hydrocephalus in BBS mutant mice. TEM analyses of the mutants showed no evidence of choroidal papillomas or breakdown of the blood:CSF barrier. In contrast, structural defects were observed in a subpopulation of cilia lining the choroid plexus, SFO, and ventricular ependyma. These included disruptions of the microtubular structure of the axoneme and the presence of electron-dense vesicular-like material along the ciliary shaft and at the tips of cilia.

Conclusions

Abnormalities in cilia structure and function have the potential to influence ciliary intraflagellar transport (IFT), cilia maintenance, protein trafficking, and regulation of CSF production. Ciliary structural defects are the only consistent pathological features associated with CSF-related structures in BBS mutant mice. These defects are observed from an early age, and may contribute to the underlying pathophysiology of ventriculomegaly.

Astrocytes acquire morphological and functional characteristics of ependymal cells following disruption of ependyma in hydrocephalus

Hydrocephalic hyh mutant mice undergo a programmed loss of the neuroepithelium/ependyma followed by a reaction of periventricular astrocytes, which form a new cell layer covering the denuded ventricular surface. We present a comparative morphological and functional study of the newly formed layer of astrocytes and the multiciliated ependyma of hyh mice. Transmission electron microscopy, immunocytochemistry for junction proteins (N-cadherin, connexin 43) and proteins involved in permeability (aquaporin 4) and endocytosis (caveolin-1, EEA1) were used. Horseradish peroxidase (HRP) and lanthanum nitrate were used to trace the intracellular and paracellular transport routes. The astrocyte layer shares several cytological features with the normal multiciliated ependyma, such as numerous microvilli projected into the ventricle, extensive cell–cell interdigitations and connexin 43-based gap junctions, suggesting that these astrocytes are coupled to play an unknown function as a cell layer. The ependyma and the astrocyte layers also share transport properties: (1) high expression of aquaporin 4, caveolin-1 and the endosome marker EEA1; (2) internalization into endocytic vesicles and early endosomes of HRP injected into the ventricle; (3) and a similar paracellular route of molecules moving between CSF, the subependymal neuropile and the pericapillary space, as shown by lanthanum nitrate and HRP. A parallel analysis performed in human hydrocephalic foetuses indicated that a similar phenomenon would occur in humans. We suggest that in foetal-onset hydrocephalus, the astrocyte assembly at the denuded ventricular walls functions as a CSF–brain barrier involved in water and solute transport, thus contributing to re-establish lost functions at the brain parenchyma–CSF interphase.

Junctional adhesion molecule (JAM)-C deficient C57BL/6 mice develop a severe hydrocephalus

The junctional adhesion molecule (JAM)-C is a widely expressed adhesion molecule regulating cell adhesion, cell polarity and inflammation. JAM-C expression and function in the central nervous system (CNS) has been poorly characterized to date. Here we show that JAM-C^−/− mice backcrossed onto the C57BL/6 genetic background developed a severe hydrocephalus. An in depth immunohistochemical study revealed specific immunostaining for JAM-C in vascular endothelial cells in the CNS parenchyma, the meninges and in the choroid plexus of healthy C57BL/6 mice. Additional JAM-C immunostaining was detected on ependymal cells lining the ventricles and on choroid plexus epithelial cells. Despite the presence of hemorrhages in the brains of JAM-C^−/− mice, our study demonstrates that development of the hydrocephalus was not due to a vascular function of JAM-C as endothelial re-expression of JAM-C failed to rescue the hydrocephalus phenotype of JAM-C^−/− C57BL/6 mice. Evaluation of cerebrospinal fluid (CSF) circulation within the ventricular system of JAM-C^−/− mice excluded occlusion of the cerebral aqueduct as the cause of hydrocephalus development but showed the acquisition of a block or reduction of CSF drainage from the lateral to the 3^rd ventricle in JAM-C^−/− C57BL/6 mice. Taken together, our study suggests that JAM-C^−/− C57BL/6 mice model the important role for JAM-C in brain development and CSF homeostasis as recently observed in humans with a loss-of-function mutation in JAM-C.

In vitro effects of fetal rat cerebrospinal fluid on viability and neuronal differentiation of PC12 cells

Background

Fetal cerebrospinal fluid (CSF) contains many neurotrophic and growth factors and has been shown to be capable of supporting viability, proliferation and differentiation of primary cortical progenitor cells. Rat pheochromocytoma PC12 cells have been widely used as an in vitro model of neuronal differentiation since they differentiate into sympathetic neuron-like cells in response to growth factors. This study aimed to establish whether PC12 cells were responsive to fetal CSF and therefore whether they might be used to investigate CSF physiology in a stable cell line lacking the time-specific response patterns of primary cells previously described.

Methods

In vitro assays of viability, proliferation and differentiation were carried out after incubation of PC12 cells in media with and without addition of fetal rat CSF. An MTT tetrazolium assay was used to assess cell viability and/or cell proliferation. Expression of neural differentiation markers (MAP-2 and β-III tubulin) was determined by immunocytochemistry. Formation and growth of neurites was measured by image analysis.

Results

PC12 cells differentiate into neuronal cell types when exposed to bFGF. Viability and cell proliferation of PC12 cells cultured in CSF-supplemented medium from E18 rat fetuses were significantly elevated relative to the control group. Neuronal-like outgrowths from cells appeared following the application of bFGF or CSF from E17 and E19 fetuses but not E18 or E20 CSF. Beta-III tubulin was expressed in PC12 cells cultured in any media except that supplemented with E18 CSF. MAP-2 expression was found in control cultures and in those with E17 and E19 CSF. MAP2 was located in neurites except in E17 CSF when the whole cell was positive.

Conclusions

Fetal rat CSF supports viability and stimulates proliferation and neurogenic differentiation of PC12 cells in an age-dependent way, suggesting that CSF composition changes with age. This feature may be important in vivo for the promotion of normal brain development. There were significant differences in the effects on PC12 cells compared to primary cortical cells. This suggests there is an interaction in vivo between developmental stage of cells and the composition of CSF. The data presented here support an important, perhaps driving role for CSF composition, specifically neurotrophic factors, in neuronal survival, proliferation and differentiation. The effects of CSF on PC12 cells can thus be used to further investigate the role of CSF in driving development without the confounding issues of using primary cells.

Dysregulation of Kruppel-like factor 4 during brain development leads to hydrocephalus in mice

Kruppel-like factor 4 (KLF4) is involved in self-renewal of embryonic stem cells and reprogramming of somatic cells to pluripotency. However, its role in lineage-committed stem cells remains largely unknown. Here, we show that KLF4 is expressed in neural stem cells (NSCs) and is down-regulated during neuronal differentiation. Unexpectedly, enhanced expression of KLF4 reduces self-renewal of cultured NSCs and inhibits proliferation of subventricular neural precursors in transgenic mice. Mice with increased KLF4 in NSCs and NSCs-derived ependymal cells developed hydrocephalus-like characteristics, including enlarged ventricles, thinned cortex, agenesis of the corpus callosum, and significantly reduced subcommissural organ. These characteristics were accompanied by elevation of GFAP expression and astrocyte hypertrophy. The ventricular cilia, vital for cerebrospinal fluid flow, are also disrupted in the mutant mice. These results indicate that down-regulation of KLF4 is critical for neural development and its dysregulation may lead to hydrocephalus.

Congenital Hydrocephalus in Genetically Engineered Mice

There is evidence that genetic factors play a role in the complex multifactorial pathogenesis of hydrocephalus. Identification of the genes involved in the development of this neurologic disorder in animal models may elucidate factors responsible for the excessive accumulation of cerebrospinal fluid in hydrocephalic humans. The authors report here a brief summary of findings from 12 lines of genetically engineered mice that presented with autosomal recessive congenital hydrocephalus. This study illustrates the value of knockout mice in identifying genetic factors involved in the development of congenital hydrocephalus. Findings suggest that dysfunctional motile cilia represent the underlying pathogenetic mechanism in 8 of the 12 lines ( Ulk4, Nme5, Nme7, Kif27, Stk36, Dpcd, Ak7, and Ak8). The likely underlying cause in the remaining 4 lines ( RIKEN 4930444A02, Celsr2, Mboat7, and transgenic FZD3) was not determined, but it is possible that some of these could also have ciliary defects. For example, the cerebellar malformations observed in RIKEN 4930444A02 knockout mice show similarities to a number of developmental disorders, such as Joubert, Meckel-Gruber, and Bardet-Biedl syndromes, which involve mutations in cilia-related genes. Even though the direct relevance of mouse models to hydrocephalus in humans remains uncertain, the high prevalence of familial patterns of inheritance for congenital hydrocephalus in humans suggests that identification of genes responsible for development of hydrocephalus in mice may lead to the identification of homologous modifier genes and susceptibility alleles in humans. Also, characterization of mouse models can enhance understanding of important cell signaling and developmental pathways involved in the pathogenesis of hydrocephalus.

Hydrocephalus and abnormal subcommissural organ in mice lacking presenilin-1 in Wnt1 cell lineages

Presenilin-1 (PS1) is a transmembrane protein that is in many cases responsible for the development of familial Alzheimer's disease. PS1 is widely expressed in embryogenesis and is essential for neurogenesis, somitogenesis, angiogenesis, and cardiac morphogenesis. To further investigate the role of PS1 in the brain, we inactivated the PS1 gene in Wnt1 cell lineages using the Cre-loxP recombination system. Here we show that conditional inactivation of PS1 in Wnt1 cell lineages results in congenital hydrocephalus and subcommissural organ abnormalities, suggesting a possible role of PS1 in the regulation of cerebrospinal fluid homeostasis.

A sensitive method to analyse the effect of putative regulatory ligands on the release of glycoprotein from primary cultures of dispersed bovine subcommissural organ cells

The subcommissural organ (SCO) releases into the cerebrospinal fluid (CSF) large glycoproteins that polymerize forming the Reissner's fibre (RF), which is involved in CSF circulation and homeostasis. We obtained high purity primary cultures of bovine secretory SCO cells and measured glycoprotein release by a reliable and sensitive ELISA method. We also analysed the effect of regulatory ligands known to control the secretory activity of the SCO. Cells cultured for short time (4h) released a high amount of glycoproteins that decreased with time. In young cultures, ATP increased and serotonin inhibited secretion rate. By contrast the acetylcholine agonist carbachol and high potassium did not evoke any detectable change in SCO glycoprotein release. These results support not only the suitability of the methodological approach but an important role of both ATP and serotonin in regulating SCO secretory activity as well.

The design of barriers in the hypothalamus allows the median eminence and the arcuate nucleus to enjoy private milieus: the former opens to the portal blood and the latter to the cerebrospinal fluid

The blood-brain barrier (BBB) is a single uninterrupted barrier that in the brain capillaries is located at the endothelial cells and in the circumventricular organs, such as the choroid plexuses (CP) and median eminence (ME), is displaced to specialized ependymal cells. How do hypothalamic hormones reach the portal circulation without making the BBB leaky? The ME milieu is open to the portal vessels, while it is closed to the cerebrospinal fluid (CSF) and to the arcuate nucleus. The cell body and most of the axons of neurons projecting to the ME are localized in areas protected by the BBB, while the axon terminals are localized in the BBB-free area of the ME. This design implies a complex organization of the intercellular space of the median basal hypothalamus. The privacy of the ME milieu implies that those neurons projecting to this area would not be under the influence of compounds leaking from the portal capillaries, unless receptors for such compounds are located at the axon terminal. Amazingly, the arcuate nucleus also has its private milieu that is closed to all adjacent neural structures and open to the infundibular recess. The absence of multiciliated cells in this recess should result in a slow CSF flow at this level. This whole arrangement should facilitate the arrival of CSF signal to the arcuate nucleus. This review will show how peripheral hormones can reach hypothalamic targets without making the BBB leaky.

The regulation of brain states by neuroactive substances distributed via the cerebrospinal fluid; a review

The cerebrospinal fluid (CSF) system provides nutrients to and removes waste products from the brain. Recent findings suggest, however, that in addition, the CSF contains message molecules in the form of actively released neuroactive substances. The concentrations of these vary between locations, suggesting they are important for the changes in brain activity that underlie different brain states, and induce different sensory input and behavioral output relationships.The cranial CSF displays a rapid caudally-directed ventricular flow followed by a slower rostrally-directed subarachnoid flow (mainly towards the cribriform plate and from there into the nasal lymphatics). Thus, many brain areas are exposed to and can be influenced by substances contained in the CSF. In this review we discuss the production and flow of the CSF, including the mechanisms involved in the regulation of its composition. In addition, the available evidence for the release of neuropeptides and other neuroactive substances into the CSF is reviewed, with particular attention to the selective effects of these on distant downstream receptive brain areas. As a conclusion we suggest that (1) the flowing CSF is involved in more than just nutrient and waste control, but is also used as a broadcasting system consisting of coordinated messages to a variety of nearby and distant brain areas; (2) this special form of volume transmission underlies changes in behavioral states.

Ependymal cells: biology and pathology

The literature was reviewed to summarize the current understanding of the role of ciliated ependymal cells in the mammalian brain. Previous reviews were summarized. Publications from the past 10 years highlight interactions between ependymal cells and the subventricular zone and the possible role of restricted ependymal populations in neurogenesis. Ependymal cells provide trophic support and possibly metabolic support for progenitor cells. Channel proteins such as aquaporins may be important for determining water fluxes at the ventricle wall. The junctional and anchoring proteins are now fairly well understood, as are proteins related to cilia function. Defects in ependymal adhesion and cilia function can cause hydrocephalus through several different mechanisms, one possibility being loss of patency of the cerebral aqueduct. Ependymal cells are susceptible to infection by a wide range of common viruses; while they may act as a line of first defense, they eventually succumb to repeated attacks in long-lived organisms. Ciliated ependymal cells are almost certainly important during brain development. However, the widespread absence of ependymal cells from the adult human lateral ventricles suggests that they may have only regionally restricted value in the mature brain of large size.

SCO-ping out the mechanisms underlying the etiology of hydrocephalus

The heterogeneous nature of congenital hydrocephalus has hampered our understanding of the molecular basis of this common clinical problem. However, disease gene identification and characterization of multiple transgenic mouse models has highlighted the importance of the subcommissural organ (SCO) and the ventricular ependymal (vel) cells. Here, we review how altered development and function of the SCO and vel cells contributes to hydrocephalus.

Congenital hydrocephalus associated with abnormal subcommissural organ in mice lacking huntingtin in Wnt1 cell lineages

Huntingtin (htt) is a 350 kDa protein of unknown function, with no homologies with other known proteins. Expansion of a polyglutamine stretch at the N-terminus of htt causes Huntington's disease (HD), a dominant neurodegenerative disorder. Although it is generally accepted that HD is caused primarily by a gain-of-function mechanism, recent studies suggest that loss-of-function may also be part of HD pathogenesis. Huntingtin is an essential protein in the mouse since inactivation of the mouse HD homolog (Hdh) gene results in early embryonic lethality. Huntingtin is widely expressed in embryogenesis, and associated with a number of interacting proteins suggesting that htt may be involved in several processes including morphogenesis, neurogenesis and neuronal survival. To further investigate the role of htt in these processes, we have inactivated the Hdh gene in Wnt1 cell lineages using the Cre-loxP system of recombination. Here we show that conditional inactivation of the Hdh gene in Wnt1 cell lineages results in congenital hydrocephalus, implicating huntingtin for the first time in the regulation of cerebral spinal fluid (CSF) homeostasis. Our results show that hydrocephalus in mice lacking htt in Wnt1 cell lineages is associated with increase in CSF production by the choroid plexus, and abnormal subcommissural organ.