Administration of FGF-2 to embryonic mouse brain induces hydrocephalic brain morphology and aberrant differentiation of neurons in the postnatal cerebral cortex

Development of the brain ventricular system from a comparative perspective

The brain ventricular system (BVS) consists of brain ventricles and channels filled with cerebrospinal fluid (CSF). Disturbance of CSF flow has been linked to scoliosis and neurodegenerative diseases, including hydrocephalus. This could be due to defects of CSF production by the choroid plexus or impaired CSF movement over the ependyma dependent on motile cilia. Most vertebrates have horizontal body posture. They retain additional evolutionary innovations assisting CSF flow, such as the Reissner fiber. The causes of hydrocephalus have been studied using animal models including rodents (mice, rats, hamsters) and zebrafish. However, the horizontal body posture reduces the effect of gravity on CSF flow, which limits the use of mammalian models for scoliosis. In contrast, fish swim against the current and experience a forward-to-backward mechanical force akin to that caused by gravity in humans. This explains the increased popularity of the zebrafish model for studies of scoliosis. "Slit-ventricle" syndrome is another side of the spectrum of BVS anomalies. It develops because of insufficient inflation of the BVS. Recent advances in zebrafish functional genetics have revealed genes that could regulate the development of the BVS and CSF circulation. This review will describe the BVS of zebrafish, a typical teleost, and vertebrates in general, in comparative perspective. It will illustrate the usefulness of the zebrafish model for developmental studies of the choroid plexus (CP), CSF flow and the BVS.

Fibroblast growth factor 2: Role in prenatal alcohol-induced stimulation of hypothalamic peptide neurons

Prenatal alcohol exposure (PAE) increases alcohol consumption and risk for alcohol use disorder. This phenomenon in rodents is suggested to involve a stimulatory effect of PAE, in female more than male offspring, on neurogenesis and density of neurons expressing neuropeptides in lateral hypothalamus (LH), including melanin-concentrating hormone (MCH), known to promote alcohol intake. With evidence suggesting a role for fibroblast growth factor 2 (FGF2) and its receptor FGFR1 in stimulating neurogenesis and alcohol drinking, we investigated here whether the FGF2-FGFR1 system is involved in the PAE-induced increase in MCH neurons, in postnatal offspring of pregnant rats given ethanol orally (embryonic day 10-15) at a low-moderate (2 g/kg/day) or high (5 g/kg/day) dose. Our results demonstrate that PAE at the low-moderate but not high dose stimulates FGF2 and FGFR1 gene expression and increases the density of MCH neurons co-expressing FGF2, only in females, but FGFR1 in both sexes. PAE induces this effect in the dorsal but not ventral area of the LH. Further analysis of FGF2 and FGFR1 transcripts within individual MCH neurons reveals an intracellular, sex-dependent effect, with PAE increasing FGF2 transcripts positively related to FGFR1 in the nucleus as well as cytoplasm of females but transcripts only in the cytoplasm of males. Peripheral injection of FGF2 itself (80 μg/kg, s.c.) in pregnant rats mimics these effects of PAE. Together, these results support the involvement of the FGF2-FGFR1 system in mediating the PAE-induced, sex dependent increase in density of MCH neurons, possibly contributing to increased alcohol consumption in the offspring.

Molecular Mechanisms and Risk Factors for the Pathogenesis of Hydrocephalus

Hydrocephalus is a neurological condition due to the aberrant circulation and/or obstruction of cerebrospinal fluid (CSF) flow with consequent enlargement of cerebral ventricular cavities. However, it is noticed that a lot of patients may still go through symptomatic progression despite standard shunting procedures, suggesting that hydrocephalus is far more complicated than a simple CSF circulative/obstructive disorder. Growing evidence indicates that genetic factors play a fundamental role in the pathogenesis of some hydrocephalus. Although the genetic research of hydrocephalus in humans is limited, many genetic loci of hydrocephalus have been defined in animal models. In general, the molecular abnormalities involved in the pathogenesis of hydrocephalus include brain development and ependymal cell dysfunction, apoptosis, inflammation, free radical generation, blood flow, and cerebral metabolism. Moreover, recent studies have indicated that the molecular abnormalities relevant to aberrant cerebral glymphatic drainage turn into an attractive subject in the CSF circulation disorder. Furthermore, the prevalent risk factors could facilitate the development of hydrocephalus. In this review, we elicited some possible fundamental molecular mechanisms and facilitating risk factors involved in the pathogenesis of hydrocephalus, and aimed to widen the diagnosis and therapeutic strategies for hydrocephalus management. Such knowledge could be used to improve patient care in different ways, such as early precise diagnosis and effective therapeutic regimens.

Overlapping migratory mechanisms between neural progenitor cells and brain tumor stem cells

Neural stem cells present in the subventricular zone (SVZ), the largest neurogenic niche of the mammalian brain, are able to self-renew as well as generate neural progenitor cells (NPCs). NPCs are highly migratory and traverse the rostral migratory stream (RMS) to the olfactory bulb, where they terminally differentiate into mature interneurons. NPCs from the SVZ are some of the few cells in the CNS that migrate long distances during adulthood. The migratory process of NPCs is highly regulated by intracellular pathway activation and signaling from the surrounding microenvironment. It involves modulation of cell volume, cytoskeletal rearrangement, and isolation from compact extracellular matrix. In malignant brain tumors including high-grade gliomas, there are cells called brain tumor stem cells (BTSCs) with similar stem cell characteristics to NPCs but with uncontrolled cell proliferation and contribute to tumor initiation capacity, tumor progression, invasion, and tumor maintenance. These BTSCs are resistant to chemotherapy and radiotherapy, and their presence is believed to lead to tumor recurrence at distal sites from the original tumor location, principally due to their high migratory capacity. BTSCs are able to invade the brain parenchyma by utilizing many of the migratory mechanisms used by NPCs. However, they have an increased ability to infiltrate the tight brain parenchyma and utilize brain structures such as myelin tracts and blood vessels as migratory paths. In this article, we summarize recent findings on the mechanisms of cellular migration that overlap between NPCs and BTSCs. A better understanding of the intersection between NPCs and BTSCs will to provide a better comprehension of the BTSCs' invasive capacity and the molecular mechanisms that govern their migration and eventually lead to the development of new therapies to improve the prognosis of patients with malignant gliomas.

Cytosine-5 RNA Methylation Regulates Neural Stem Cell Differentiation and Motility

Loss-of-function mutations in the cytosine-5 RNA methylase NSUN2 cause neurodevelopmental disorders in humans, yet the underlying cellular processes leading to the symptoms that include microcephaly remain unclear. Here, we show that NSUN2 is expressed in early neuroepithelial progenitors of the developing human brain, and its expression is gradually reduced during differentiation of human neuroepithelial stem (NES) cells in vitro. In the developing Nsun2-/- mouse cerebral cortex, intermediate progenitors accumulate and upper-layer neurons decrease. Loss of NSUN2-mediated methylation of tRNA increases their endonucleolytic cleavage by angiogenin, and 5' tRNA fragments accumulate in Nsun2-/- brains. Neural differentiation of NES cells is impaired by both NSUN2 depletion and the presence of angiogenin. Since repression of NSUN2 also inhibited neural cell migration toward the chemoattractant fibroblast growth factor 2, we conclude that the impaired differentiation capacity in the absence of NSUN2 may be driven by the inability to efficiently respond to growth factors.

The Genetic Basis of Hydrocephalus

Studies of syndromic hydrocephalus have led to the identification of >100 causative genes. Even though this work has illuminated numerous pathways associated with hydrocephalus, it has also highlighted the fact that the genetics underlying this phenotype are more complex than anticipated originally. Mendelian forms of hydrocephalus account for a small fraction of the genetic burden, with clear evidence of background-dependent effects of alleles on penetrance and expressivity of driver mutations in key developmental and homeostatic pathways. Here, we synthesize the currently implicated genes and inheritance paradigms underlying hydrocephalus, grouping causal loci into functional modules that affect discrete, albeit partially overlapping, cellular processes. These in turn have the potential to both inform pathomechanism and assist in the rational molecular classification of a clinically heterogeneous phenotype. Finally, we discuss conceptual methods that can lead to enhanced gene identification and dissection of disease basis, knowledge that will potentially form a foundation for the design of future therapeutics.

Imaging of spontaneous ventriculomegaly and vascular malformations in Wistar rats: implications for preclinical research

Wistar rats are widely used in biomedical research and commonly serve as a model organism in neuroscience studies. In most cases when noninvasive imaging is not used, studies assume a consistent baseline condition in rats that lack visible differences. While performing a series of traumatic brain injury studies, we discovered mild spontaneous ventriculomegaly in 70 (43.2%) of 162 Wistar rats that had been obtained from 2 different vendors. Advanced magnetic resonance (MR) imaging techniques, including MR angiography and diffusion tensor imaging, were used to evaluate the rats. Multiple neuropathologic abnormalities, including presumed arteriovenous malformations, aneurysms, cysts, white matter lesions, and astrogliosis were found in association with ventriculomegaly. Postmortem microcomputed tomography and immunohistochemical staining confirmed the presence of aneurysms and arteriovenous malformations. Diffusion tensor imaging showed significant decreases in fractional anisotropy and increases in mean diffusivity, axial diffusivity, and radial diffusivity in multiple white matter tracts (p < 0.05). These results could impact the interpretation, for example, of a pseudo-increase of axon integrity and a pseudo-decrease of myelin integrity, based on characteristics intrinsic to rats with ventriculomegaly. We suggest the use of baseline imaging to prevent the inadvertent introduction of a high degree of variability in preclinical studies of neurologic disease or injury in Wistar rats.

Disruption of wave-associated Rac GTPase-activating protein (Wrp) leads to abnormal adult neural progenitor migration associated with hydrocephalus

Hydrocephalus is the most common developmental disability and leading cause of brain surgery for children. Current treatments are limited to surgical intervention, as the factors that contribute to the initiation of hydrocephalus are poorly understood. Here, we describe the development of obstructive hydrocephalus in mice that are null for Wrp (Srgap3). Wrp is highly expressed in the ventricular stem cell niche, and it is a gene required for cytoskeletal organization and is associated with syndromic and psychiatric disorders in humans. During the postnatal period of progenitor cell expansion and ventricular wall remodeling, loss of Wrp results in the abnormal migration of lineage-tagged cells from the ventricular region into the corpus callosum. Within this region, mutant progenitors appear to give rise to abnormal astroglial cells and induce periventricular lesions and hemorrhage that leads to cerebral aqueductal occlusion. These results indicate that periventricular abnormalities arising from abnormal migration from the ventricular niche can be an initiating cause of noncommunicating hydrocephalus.

Expansion, folding, and abnormal lamination of the chick optic tectum after intraventricular injections of FGF2

Comparative research has shown that evolutionary increases in brain region volumes often involve delays in neurogenesis. However, little is known about the influence of such changes on subsequent development. To get at this question, we injected FGF2--which delays cell cycle exit in mammalian neocortex--into the cerebral ventricles of chicks at embryonic day (ED) 4. This manipulation alters the development of the optic tectum dramatically. By ED7, the tectum of FGF2-treated birds is abnormally thin and has a reduced postmitotic layer, consistent with a delay in neurogenesis. FGF2 treatment also increases tectal volume and ventricular surface area, disturbs tectal lamination, and creates small discontinuities in the pia mater overlying the tectum. On ED12, the tectum is still larger in FGF2-treated embryos than in controls. However, lateral portions of the FGF2-treated tectum now exhibit volcano-like laminar disturbances that coincide with holes in the pia, and the caudomedial tectum exhibits prominent folds. To explain these observations, we propose that the tangential expansion of the ventricular surface in FGF2-treated tecta outpaces the expansion of the pial surface, creating abnormal mechanical stresses. Two alternative means of alleviating these stresses are tectal foliation and the formation of pial holes. The latter probably alter signaling gradients required for normal cell migration and may generate abnormal patterns of cerebrospinal fluid flow; both abnormalities would generate disturbances in tectal lamination. Overall, our findings suggest that evolutionary expansion of sheet-like, laminated brain regions requires a concomitant expansion of the pia mater.

Expression of sorting nexin 12 is regulated in developing cerebral cortical neurons

The sorting nexins (SNXs) are a family of proteins functioning in diverse processes, including endocytosis, endosomal sorting, and endosomal signaling. Sorting nexin 12 (SNX12) is one of the SNXs family members; however, its function remains unknown. To clarify the function of SNX12, in this study, we first investigated the expression profiles in mice, particularly in the central nervous system (CNS), and then analyzed the functional role on neurite outgrowth. We found that SNX12 was widely expressed in the adult mouse CNS and that its expression level was higher in the cerebral cortex than in other examined regions. SNX12 expression was detected in the neurons but not the glial cells of the adult mouse cerebral cortex. In the fetal brain, SNX12 expression increased during the embryonic stage and gradually decreased after birth. Although the immunoreactivities of SNX12 were widespread in the cerebral cortical cells in the fetal brain, the immunopositive signals of SNX12 were more intense in the postmitotic neurons in the cortical plate than in the proliferating precursor cells in the ventricular zone, suggesting that SNX12 plays critical roles in the postmitotic neurons during cerebral cortical development. Furthermore, in mouse neuroblastoma and N1E-115 cells and rat primary cortical neurons, SNX12 expression was increased as neurite outgrowth progressed and the knockdown of SNX12 attenuated the outgrowth of neurites. These results suggest that SNX12 regulates neurite formation during cerebral cortical development.

Dynamic roles of FGF-2 and Anosmin-1 in the migration of neuronal precursors from the subventricular zone during pre- and postnatal development

FGF-2 and Anosmin-1 are diffusible proteins which act in cell proliferation and/or migration during CNS development. We describe their developmental expression patterns in the subventricular zone (SVZ) of the forebrain and the neuronal precursors (NPs) that migrate from this neurogenic site towards the olfactory bulb, forming the rostral migratory stream (RMS). The analysis is carried out before (E14), during (E17, P5) and after (P15) the peaks of migration along the RMS and before this acquires its mature conformation. At all these stages, FGF-2 exerts a FGFR1-mediated motogenic effect on NPs and induces the proliferation of SVZ astrocytes (putatively type B cells from triads), and Anosmin-1 works as a typical chemotropic agent for the NPs (mediated by FGFR1 at P5-P15). Altogether, our results are consistent with the notion that FGF-2 increases cell proliferation in the SVZ and would be the motogenic cue which feeds the migration of the newly produced NPs once generated, from early development (E14) and at least until P15, while Anosmin-1 cooperates in this migration attracting the NPs. In this sense, both cues should be considered as two of the first to be chronologically identified as actors in the formation of the RMS.

Fgf2 is expressed in human and murine embryonic choroid plexus and affects choroid plexus epithelial cell behaviour

Background

Although fibroblast growth factor (Fgf) signalling plays crucial roles in several developing and mature tissues, little information is currently available on expression of Fgf2 during early choroid plexus development and whether Fgf2 directly affects the behaviour of the choroid plexus epithelium (CPe). The purpose of this study was to investigate expression of Fgf2 in rodent and human developing CPe and possible function of Fgf2, using in vitro models. The application of Fgf2 to brain in vivo can affect the whole tissue, making it difficult to assess specific responses of the CPe.

Methods

Expression of Fgf2 was studied by immunohistochemistry in rodent and human embryonic choroid plexus. Effects of Fgf2 on growth, secretion, aggregation and gene expression was investigated using rodent CPe vesicles, a three-dimensional polarized culture model that closely mimics CPe properties in vivo, and rodent CPe monolayer cultures.

Results

Fgf2 was present early in development of the choroid plexus both in mouse and human, suggesting the importance of this ligand in Fgf signalling in the developing choroid plexus. Parallel analysis of Fgf2 expression and cell proliferation during CP development suggests that Fgf2 is not involved in CPe proliferation in vivo. Consistent with this observation is the failure of Fgf2 to increase proliferation in the tri-dimensional vesicle culture model. The CPe however, can respond to Fgf2 treatment, as the diameter of CPe vesicles is significantly increased by treatment with this growth factor. We show that this is due to an increase in cell aggregation during vesicle formation rather than increased secretion into the vesicle lumen. Finally, Fgf2 regulates expression of the CPe-associated transcription factors, Foxj1 and E2f5, whereas transthyretin, a marker of secretory activity, is not affected by Fgf2 treatment.

Conclusion

Fgf2 expression early in the development of both human and rodent choroid plexus, and its ability to modulate behaviour and gene expression in CPe, supports the view that Fgf signalling plays a role in the maintenance of integrity and function of this specialized epithelium, and that this role is conserved between rodents and humans.

Protein and synthetic polymer injection for induction of obstructive hydrocephalus in rats

Background

The objective of this study was to develop a simple and inexpensive animal model of induced obstructive hydrocephalus with minimal tissue inflammation, as an alternative to kaolin injection.

Materials

Two-hundred and two male Sprague-Dawley rats aged 3 weeks received intracisternal injections of kaolin (25% suspension), Matrigel, type 1 collagen from rat tail, fibrin glue (Tisseel), n-butyl-cyanoacrylate (NBCA), or ethylene vinyl alcohol copolymer (Onyx-18 and Onyx-34). Magnetic resonance imaging was used to assess ventricle size. Animals were euthanized at 2, 5, 10 and 14 days post-injection for histological analysis.

Results

Kaolin was associated with 10% mortality and successful induction of hydrocephalus in 97% of survivors (ventricle area proportion 0.168 ± 0.018). Rapidly hardening agents (fibrin glue, NBCA, vinyl polymer) had high mortality rates and low success rates in survivors. Only Matrigel had relatively low mortality (17%) and moderate success rate (20%). An inflammatory response with macrophages and some lymphocytes was associated with kaolin. There was negligible inflammation associated with Matrigel. A severe inflammatory response with giant cell formation was associated with ethylene vinyl alcohol copolymer.

Conclusion

Kaolin predictably produces moderate to severe hydrocephalus with a mild chronic inflammatory reaction and fibrosis of the leptomeninges. Other synthetic polymers and biopolymers tested are unreliable and cause different types of inflammation.

Genetics of human hydrocephalus

Human hydrocephalus is a common medical condition that is characterized by abnormalities in the flow or resorption of cerebrospinal fluid (CSF), resulting in ventricular dilatation. Human hydrocephalus can be classified into two clinical forms, congenital and acquired. Hydrocephalus is one of the complex and multifactorial neurological disorders.

A growing body of evidence indicates that genetic factors play a major role in the pathogenesis of hydrocephalus. An understanding of the genetic components and mechanism of this complex disorder may offer us significant insights into the molecular etiology of impaired brain development and an accumulation of the cerebrospinal fluid in cerebral compartments during the pathogenesis of hydrocephalus. Genetic studies in animal models have started to open the way for understanding the underlying pathology of hydrocephalus. At least 43 mutants/loci linked to hereditary hydrocephalus have been identified in animal models and humans. Up to date, 9 genes associated with hydrocephalus have been identified in animal models. In contrast, only one such gene has been identified in humans. Most of known hydrocephalus gene products are the important cytokines, growth factors or related molecules in the cellular signal pathways during early brain development. The current molecular genetic evidence from animal models indicate that in the early development stage, impaired and abnormal brain development caused by abnormal cellular signaling and functioning, all these cellular and developmental events would eventually lead to the congenital hydrocephalus.

Owing to our very primitive knowledge of the genetics and molecular pathogenesis of human hydrocephalus, it is difficult to evaluate whether data gained from animal models can be extrapolated to humans. Initiation of a large population genetics study in humans will certainly provide invaluable information about the molecular and cellular etiology and the developmental mechanisms of human hydrocephalus.

This review summarizes the recent findings on this issue among human and animal models, especially with reference to the molecular genetics, pathological, physiological and cellular studies, and identifies future research directions.

Genetic analysis of inherited hydrocephalus in a rat model

Congenital hydrocephalus is a serious neurological disorder with a diverse etiology. Although there is strong evidence for genetic causes, few genes have been identified in humans. The rodent model, the H-Tx rat, has hydrocephalus with an onset in late gestation and a complex mode of inheritance. Ventricular dilatation is associated with abnormalities in the cerebral aqueduct and subcommissural organ. Quantitative trait locus (QTL) mapping was performed on DNA from the progeny of a backcross with the non-hydrocephalic Fischer F344 strain, using DNA microsatellite markers. The hydrocephalus trait was quantified by measuring the severity of the ventricular dilatation. Four chromosomes, each with a locus for hydrocephalus (Chrs 9, 10, 11, and 17), were mapped using additional markers and DNA from four subsets of backcross progeny with allelic recombination at or near each locus. The genetic positions for the markers and the loci were located using the Ensemble Rat Genome Browser. For each chromosome studied, the interval containing the locus was examined for known rat genes and for human genes identified from human-rat homology. Genes expressed in brain and with a function associated with known causes of hydrocephalus were identified as possible candidate genes. Future studies to characterize the causative genes in this animal model will improve the understanding of genetic causes in humans.

Brain-derived neurotrophic factor alters cell migration of particular progenitors in the developing mouse cerebral cortex

Effects of brain-derived neurotrophic factor (BDNF) on cell migration from the ventricular zone to the cortical plate (CP) in developing mouse cerebral cortex were examined. BDNF (700 ng) was injected into the brain ventricle of 13- or 14-day-old embryos (E13 or E14) after the intraperitoneal administration of 5-bromodeoxyuridine (BrdU) to pregnant mice. BDNF injection at E13 increased the number of BrdU-positive cells migrated into the CP until E15, and caused them to become localized in much deeper layers (V-VI) than expected (IV-V, as in the vehicle-treated mice) by postnatal day 1. However, when the injections were made at E14, BrdU-positive cells predominantly migrated to layers II/III irrespective of BDNF administration. These results demonstrate that BDNF affects particular progenitors at limited stages, and suggest the presence of a Reelin-independent mechanism(s) to regulate cell migration.