Embryonic cerebrospinal fluid collaborates with the isthmic organizer to regulate mesencephalic gene expression

Accumulation of Cerebrospinal Fluid, Ventricular Enlargement, and Cerebral Folate Metabolic Errors Unify a Diverse Group of Neuropsychiatric Conditions Affecting Adult Neocortical Functions

Cerebrospinal fluid (CSF) is a fluid critical to brain development, function, and health. It is actively secreted by the choroid plexus, and it emanates from brain tissue due to osmolar exchange and the constant contribution of brain metabolism and astroglial fluid output to interstitial fluid into the ventricles of the brain. CSF acts as a growth medium for the developing cerebral cortex and a source of nutrients and signalling throughout life. Together with perivascular glymphatic and interstitial fluid movement through the brain and into CSF, it also acts to remove toxins and maintain metabolic balance. In this study, we focused on cerebral folate status, measuring CSF concentrations of folate receptor alpha (FOLR1); aldehyde dehydrogenase 1L1, also known as 10-formyl tetrahydrofolate dehydrogenase (ALDH1L1 and FDH); and total folate. These demonstrate the transport of folate from blood across the blood-CSF barrier and into CSF (FOLR1 + folate), and the transport of folate through the primary FDH pathway from CSF into brain FDH + ve astrocytes. Based on our hypothesis that CSF flow, drainage issues, or osmotic forces, resulting in fluid accumulation, would have an associated cerebral folate imbalance, we investigated folate status in CSF from neurological conditions that have a severity association with enlarged ventricles. We found that all the conditions we examined had a folate imbalance, but these folate imbalances were not all the same. Given that folate is essential for key cellular processes, including DNA/RNA synthesis, methylation, nitric oxide, and neurotransmitter synthesis, we conclude that ageing or some form of trauma in life can lead to CSF accumulation and ventricular enlargement and result in a specific folate imbalance/deficiency associated with the specific neurological condition. We believe that addressing cerebral folate imbalance may therefore alleviate many of the underlying deficits and symptoms in these conditions.

E3 Ubiquitin Ligase Uhrf2 Knockout Reveals a Critical Role in Social Behavior and Synaptic Plasticity in the Hippocampus

The hippocampal formation, particularly the CA2 subregion, is critical for social memory formation and memory processing, relying on synaptic plasticity-a fundamental mechanism by which synapses strengthen. Given the role of the ubiquitin-proteasome system (UPS) in various nervous system processes, including learning and memory, we were particularly interested in exploring the involvement of RING-type ubiquitin E3 ligases, such as UHRF2 (NIRF), in social behavior and synaptic plasticity. Our results revealed altered social behavior in mice with systemic Uhrf2 knockout, including changes in nest building, tube dominance, and the three-chamber social novelty test. In Uhrf2 knockout mice, the entorhinal cortex-CA2 circuit showed significant reductions in synaptic plasticity during paired-pulse facilitation and long-term potentiation, while the inability to evoke synaptic plasticity in the Schaffer-collateral CA2 synapses remained unaffected. These changes in synaptic plasticity correlated with significant changes in gene expression including genes related to vesicle trafficking and transcriptional regulation. The effects of Uhrf2 knockout on synaptic plasticity and the observed gene expression changes highlight UHRF2 as a regulator of learning and memory processes at both the cellular and systemic levels. Targeting E3 ubiquitin ligases, such as UHRF2, may hold therapeutic potential for memory-related disorders, warranting further investigation.

Deciphering the impact of cerebrospinal fluid on stem cell fate as a new mechanism to enhance clinical therapy development

Neural stem cells (NSCs) hold a very significant promise as candidates for cell therapy due to their robust neuroprotective and regenerative properties. Preclinical studies using NSCs have shown enough encouraging results to perform deeper investigations into more potential clinical applications. Nevertheless, our knowledge regarding neurogenesis and its underlying mechanisms remains incomplete. To understand them better, it seems necessary to characterize all components of neural stem cell niche and discover their role in physiology and pathology. Using NSCs in vivo brings challenges including limited cell survival and still inadequate integration within host tissue. Identifying overlooked factors that might influence these outcomes becomes pivotal. In this review, we take a deeper examination of the influence of a fundamental element that is present in the brain, the cerebrospinal fluid (CSF), which still remains relatively unexplored. Its role in neurogenesis could be instrumental to help find novel therapeutic solutions for neurological disorders, eventually advancing our knowledge on central nervous system (CNS) regeneration and repair.

Choroid Plexus: The Orchestrator of Long-Range Signalling Within the CNS

Cerebrospinal fluid (CSF) is the liquid that fills the brain ventricles. CSF represents not only a mechanical brain protection but also a rich source of signalling factors modulating diverse processes during brain development and adulthood. The choroid plexus (CP) is a major source of CSF and as such it has recently emerged as an important mediator of extracellular signalling within the brain. Growing interest in the CP revealed its capacity to release a broad variety of bioactive molecules that, via CSF, regulate processes across the whole central nervous system (CNS). Moreover, CP has been also recognized as a sensor, responding to altered composition of CSF associated with changes in the patterns of CNS activity. In this review, we summarize the recent advances in our understanding of the CP as a signalling centre that mediates long-range communication in the CNS. By providing a detailed account of the CP secretory repertoire, we describe how the CP contributes to the regulation of the extracellular environment-in the context of both the embryonal as well as the adult CNS. We highlight the role of the CP as an important regulator of CNS function that acts via CSF-mediated signalling. Further studies of CP-CSF signalling hold the potential to provide key insights into the biology of the CNS, with implications for better understanding and treatment of neuropathological conditions.

Subarachnoid cerebrospinal fluid is essential for normal development of the cerebral cortex

The central nervous system develops around a fluid filled space which persists in the adult within the ventricles, spinal canal and around the outside of the brain and spinal cord. Ventricular fluid is known to act as a growth medium and stimulator of proliferation and differentiation to neural stem cells but the role of CSF in the subarachnoid space has not been fully investigated except for its role in the recently described "glymphatic" system. Fundamental changes occur in the control and coordination of CNS development upon completion of brain stem and spinal cord development and initiation of cortical development. These include changes in gene expression, changes in fluid and fluid source from neural tube fluid to cerebrospinal fluid (CSF), changes in fluid volume, composition and fluid flow pathway, with exit of high volume CSF into the subarachnoid space and the critical need for fluid drainage. We used a number of experimental approaches to test a predicted critical role for CSF in development of the cerebral cortex in rodents and humans. Data from fetuses affected by spina bifida and/or hydrocephalus are correlated with experimental evidence on proliferation and migration of cortical cells from the germinal epithelium in rodent neural tube defects, as well as embryonic brain slice experiments demonstrating a requirement for CSF to contact both ventricular and pial surfaces of the developing cortex for normal proliferation and migration. We discuss the possibility that complications with the fluid system are likely to underlie developmental disorders affecting the cerebral cortex as well as function and integrity of the cortex throughout life.

Embryonic cerebrospinal fluid formation and regulation

The vertebrate brain is organized, from its embryonic origin and throughout adult life, around a dynamic and complex fluid, the cerebrospinal fluid (CSF). There is growing interest in the composition, dynamics and function of the CSF in brain development research. It has been demonstrated in higher vertebrates that CSF has key functions in delivering diffusible signals and nutrients to the developing brain, contributing to the proliferation, differentiation and survival of neural progenitor cells, and to the patterning of the brain. It has also been shown that the composition and the homeostasis of CSF are tightly regulated following the closure of the anterior neuropore, just before the initiation of primary neurogenesis in the neural tissue surrounding brain cavities, before the formation of functional choroid plexus. In this review we draw together existing literature about the composition and formation of embryonic cerebrospinal fluid in birds and mammals, from the closure of the anterior neuropore to the formation of functional fetal choroid plexus, including mechanisms regulating its composition and homeostasis. The significance of CSF regulation within embryonic brain is also discussed from an evolutionary perspective.

Functional Analyses of Embryonic Cerebrospinal Fluid Proteins

The embryonic cerebrospinal fluid (eCSF) influences neuroepithelial cell behavior, affecting proliferation, differentiation, and survival. One major question to resolve in the field is to precisely describe the eCSF molecules responsible and to understand how these molecules interact in order to exert their functions. Here we describe an in vitro protocol to analyze the influence of eCSF components on neuroepithelium development.

Cerebrospinal fluid-stem cell interactions may pave the path for cell-based therapy in neurological diseases

Recent studies have suggested that the regulation of endogenous neural stem cells (NSCs) or transplanting of exogenous nerve cells are the newest and most promising methods for the treatment of dementia and other neurological diseases. The special location and limited number of endogenous NSCs, however, restrict their clinical application. The success in directional differentiation of exogenous stem cells from other tissue sources into neural cells has provided a novel source for NSCs. Study on the relative mechanisms is still at the preliminary stage. Currently the induction methods include: 1) cell growth factor induction; 2) chemical induction; 3) combined growth factor-chemical induction; or 4) other induction methods such as traumatic brain tissue homogenate, gene transfection, traditional Chinese medicine, and coculture induction. Cerebrospinal fluid (CSF), as a natural medium under physiological conditions, contains a variety of progrowth peptide factors that can promote the proliferation and differentiation of mesenchymal stromal cells (MSCs) into neural cells through the corresponding receptors on the cell surface. This suggests that CSF can not only nourish the nerve cells, but also become an effective and suitable inducer to increase the yield of NSCs. However, some other studies believed that CSF contained certain inhibitory components against the differentiation of primary stem cells into mature neural cells. Based on the above background, here we review the relative literature on the influence of the CSF on stem cells in order to provide a more comprehensive reference for the wide clinical application of NSCs in the future.

Embryonic Cerebrospinal Fluid Increases Neurogenic Activity in the Brain Ventricular-Subventricular Zone of Adult Mice

Neurogenesis is a very intensive process during early embryonic brain development, becoming dramatically restricted in the adult brain in terms of extension and intensity. We have previously demonstrated the key role of embryonic cerebrospinal fluid (CSF) in developing brain neurogenic activity. We also showed that cultured adult brain neural stem cells (NSCs) remain competent when responding to the neurogenic influence of embryonic CSF. However, adult CSF loses its neurogenic inductive properties. Here, by means of an organotypic culture of adult mouse brain sections, we show that local administration of embryonic CSF in the subventricular zone (SVZ) niche is able to trigger a neurogenic program in NSCs. This leads to a significant increase in the number of non-differentiated NSCs, and also in the number of new neurons which show normal migration, differentiation and maturation. These new data reveal that embryonic CSF activates adult brain NSCs, supporting the previous idea that it contains key instructive components which could be useful in adult brain neuroregenerative strategies.

Midbrain-Hindbrain Boundary Morphogenesis: At the Intersection of Wnt and Fgf Signaling

A constriction in the neural tube at the junction of the midbrain and hindbrain is a conserved feature of vertebrate embryos. The constriction is a defining feature of the midbrain-hindbrain boundary (MHB), a signaling center that patterns the adjacent midbrain and rostral hindbrain and forms at the junction of two gene expression domains in the early neural plate: an anterior otx2/wnt1 positive domain and a posterior gbx/fgf8 positive domain. otx2 and gbx genes encode mutually repressive transcription factors that create a lineage restriction boundary at their expression interface. Wnt and Fgf genes form a mutually dependent feedback system that maintains their expression domains on the otx2 or gbx side of the boundary, respectively. Constriction morphogenesis occurs after these conserved gene expression domains are established and while their mutual interactions maintain their expression pattern; consequently, mutant studies in zebrafish have led to the suggestion that constriction morphogenesis should be considered a unique phase of MHB development. We analyzed MHB morphogenesis in fgf8 loss of function zebrafish embryos using a reporter driven by the conserved wnt1 enhancer to visualize anterior boundary cells. We found that fgf8 loss of function results in a re-activation of wnt1 reporter expression posterior to the boundary simultaneous with an inactivation of the wnt1 reporter in the anterior boundary cells, and that these events correlate with relaxation of the boundary constriction. In consideration of other results that correlate the boundary constriction with Wnt and Fgf expression, we propose that the maintenance of an active Wnt-Fgf feedback loop is a key factor in driving the morphogenesis of the MHB constriction.

Evolutionary development of embryonic cerebrospinal fluid composition and regulation: an open research field with implications for brain development and function

Within the consolidated field of evolutionary development, there is emerging research on evolutionary aspects of central nervous system development and its implications for adult brain structure and function, including behaviour. The central nervous system is one of the most intriguing systems in complex metazoans, as it controls all body and mind functions. Its failure is responsible for a number of severe and largely incurable diseases, including neurological and neurodegenerative ones. Moreover, the evolution of the nervous system is thought to be a critical step in the adaptive radiation of vertebrates. Brain formation is initiated early during development. Most embryological, genetic and evolutionary studies have focused on brain neurogenesis and regionalisation, including the formation and function of organising centres, and the comparison of homolog gene expression and function among model organisms from different taxa. The architecture of the vertebrate brain primordium also reveals the existence of connected internal cavities, the cephalic vesicles, which in fetuses and adults become the ventricular system of the brain. During embryonic and fetal development, brain cavities and ventricles are filled with a complex, protein-rich fluid called cerebrospinal fluid (CSF). However, CSF has not been widely analysed from either an embryological or evolutionary perspective. Recently, it has been demonstrated in higher vertebrates that embryonic cerebrospinal fluid has key functions in delivering diffusible signals and nutrients to the developing brain, thus contributing to the proliferation, differentiation and survival of neural progenitor cells, and to the expansion and patterning of the brain. Moreover, it has been shown that the composition and homeostasis of CSF are tightly controlled in a time-dependent manner from the closure of the anterior neuropore, just before the initiation of primary neurogenesis, up to the formation of functional choroid plexuses. In this review, we draw together existing literature about the formation, function and homeostatic regulation of embryonic cerebrospinal fluid, from the closure of the anterior neuropore to the formation of functional fetal choroid plexuses, from an evolutionary perspective. The relevance of these processes to the normal functions and diseases of adult brain will also be discussed.

Zebrafish cerebrospinal fluid mediates cell survival through a retinoid signaling pathway

Cerebrospinal fluid (CSF) includes conserved factors whose function is largely unexplored. To assess the role of CSF during embryonic development, CSF was repeatedly drained from embryonic zebrafish brain ventricles soon after their inflation. Removal of CSF increased cell death in the diencephalon, indicating a survival function. Factors within the CSF are required for neuroepithelial cell survival as injected mouse CSF but not artificial CSF could prevent cell death after CSF depletion. Mass spectrometry analysis of the CSF identified retinol binding protein 4 (Rbp4), which transports retinol, the precursor to retinoic acid (RA). Consistent with a role for Rbp4 in cell survival, inhibition of Rbp4 or RA synthesis increased neuroepithelial cell death. Conversely, ventricle injection of exogenous human RBP4 plus retinol, or RA alone prevented cell death after CSF depletion. Zebrafish rbp4 is highly expressed in the yolk syncytial layer, suggesting Rbp4 protein and retinol/RA precursors can be transported into the CSF from the yolk. In accord with this suggestion, injection of human RBP4 protein into the yolk prevents neuroepithelial cell death in rbp4 loss‐of‐function embryos. Together, these data support the model that Rbp4 and RA precursors are present within the CSF and used for synthesis of RA, which promotes embryonic neuroepithelial survival. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 75–92, 2016

The embryonic blood-cerebrospinal fluid barrier function before the formation of the fetal choroid plexus: role in cerebrospinal fluid formation and homeostasis

Cerebrospinal fluid (CSF) has attracted interest as an active signaling milieu that regulates brain development, homeostasis, and course disease. CSF is a nutrient-rich fluid, which also contains growth factors and signaling molecules that regulate multiple cell functions in the central nervous system (CNS). CSF constitution is controlled tightly and constituent concentrations are maintained narrow, depending on developmental stage. From fetal stages to adult life, CSF is produced mainly by the choroid plexus. The development and functional activities of the choroid plexus, and other blood-brain barrier systems in adults, have been extensively analyzed. However, the study of CSF production and homeostasis in embryos from the closure of the anterior neuropore, when the brain cavities become physiologically sealed, to the formation of the functional fetal choroid plexus has been largely neglected. This developmental stage is characterized by tightly controlled morphological and cellular events in the anterior part of the CNS, such as rapid brain anlagen growth and initiation of primary neurogenesis in the neural progenitor cells lining the cavities, events which are driven by specific molecules contained within the embryonic CSF. In this article, we review the existing literature on formation and function of the temporary embryonic blood-CSF barrier, from closure of the anterior neuropore to the formation of functional fetal choroid plexuses, with regard to crucial roles that embryonic CSF plays in neural development.

Embryonic blood-cerebrospinal fluid barrier formation and function

During embryonic development and adult life, brain cavities and ventricles are filled with cerebrospinal fluid (CSF). CSF has attracted interest as an active signaling medium that regulates brain development, homeostasis and disease. CSF is a complex protein-rich fluid containing growth factors and signaling molecules that regulate multiple cell functions in the central nervous system (CNS). The composition and substance concentrations of CSF are tightly controlled. In recent years, it has been demonstrated that embryonic CSF (eCSF) has a key function as a fluid pathway for delivering diffusible signals to the developing brain, thus contributing to the proliferation, differentiation and survival of neural progenitor cells, and to the expansion and patterning of the brain. From fetal stages through to adult life, CSF is primarily produced by the choroid plexus. The development and functional activities of the choroid plexus and other blood-brain barrier (BBB) systems in adults and fetuses have been extensively analyzed. However, eCSF production and control of its homeostasis in embryos, from the closure of the anterior neuropore when the brain cavities become physiologically sealed, to the formation of the functional fetal choroid plexus, has not been studied in as much depth and remains open to debate. This review brings together the existing literature, some of which is based on experiments conducted by our research group, concerning the formation and function of a temporary embryonic blood-CSF barrier in the context of the crucial roles played by the molecules in eCSF.

Fingerprint changes in CSF composition associated with different aetiologies in human neonatal hydrocephalus: inflammatory cytokines

PURPOSE

Hydrocephalus (HC) has a multifactorial and complex picture of pathophysiology due to aetiology, age at and duration since onset. We have previously identified distinctions in markers of cell death associated with different aetiologies. Here, we examined cerebrospinal fluid (CSF) from human HC neonates for cytokines to identify further distinguishing features of different aetiologies.

METHODS

CSF was collected during routine lumbar puncture or ventricular tap from neonates with hydrocephalus, or with no neurological condition (normal controls). Total protein, Fas receptor, Fas ligand, stem cell factor (SCF), hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), insulin growth factor-1 (IGF-1), tumour necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were measured and compared between 8 unaffected and 28 HC neonatal CSF samples.

RESULTS

Total protein was significantly (P < 0.05) raised in late-onset hydrocephalus (LOH). Fas receptor was raised (P < 0.05) in post-haemorrhagic hydrocephalus (PHH) and spina bifida with hydrocephalus (SB/HC), but no difference in Fas ligand was found. SCF was raised (P < 0.05) in SB/HC. HGF was found in all HC and was increased (P < 0.01) in PHH. Increased VEGF was found in PHH (P < 0.01) and SB/HC (P < 0.05). Variable levels of IL-6, TNF-α and IGF-1 were found in all HC groups compared with none in normal.

CONCLUSIONS

LOH was unusual with significantly raised total protein indicating an inflammatory state. Increased Fas receptor, VEGF, IGF-1 and HGF suggest anti-apoptotic and repair mechanism activation. By contrast, elevated TNF-α and IL-6 indicate inflammatory processes in these neonatal brains. Taken with our previous study, these data indicate that different pathophysiology, inflammation and repair are occurring in HC of different aetiologies and that additional treatment strategies may benefit these infants in addition to fluid diversion.

Neural stem cells: are they the hope of a better life for patients with fetal-onset hydrocephalus?

I was honored to be awarded the Casey Holter Essay Prize in 2013 by the Society for Research into Hydrocephalus and Spina Bifida. The purpose of the prize is to encourage original thinking in a way to improve the care of individuals with spina bifida and hydrocephalus. Having kept this purpose in mind, I have chosen the title: Neural stem cells, are they the hope of a better life for patients with fetal-onset hydrocephalus? The aim is to review and discuss some of the most recent and relevant findings regarding mechanisms leading to both hydrocephalus and abnormal neuro/gliogenesis. By looking at these outcome studies, it is hoped that we will recognize the potential use of neural stem cells in the treatment of hydrocephalus, and so prevent the disease or diminish/repair the associated brain damage.

Homeostasis of cerebrospinal fluid has a role in early brain development

Embryonic cerebrospinal fluid (E-CSF) is a protein-containing fluid present in brain cavities that plays key roles in neuronal development and function. From the beginning of primary brain neurogenesis, E-CSF composition and homeostasis are precisely tuned by a transient blood-CSF barrier function, which controls protein transport and their relative concentration of within-brain cavities. One of the proteins found in E-CSF is ovalbumin, which is postulated to play a role in nutrition. Here, we address the question of whether neuroepithelial progenitor cells in developing chick embryos use ovalbumin as a highly specific nutritional source of amino acids or alternatively whether they use other amino acid sources, despite the fact that they cannot be transported from blood serum to brain cavities under physiological conditions. Although ovalbumin was not found to be a key protein required for neurogenesis and cell survival, our observations reinforce the crucial role of the embryonic blood-CSF barrier, as its precise regulation of protein transport and E-CSF homeostasis ensures the maximum efficiency of neural development.

Manual drainage of the zebrafish embryonic brain ventricles

Cerebrospinal fluid (CSF) is a protein rich fluid contained within the brain ventricles. It is present during early vertebrate embryonic development and persists throughout life. Adult CSF is thought to cushion the brain, remove waste, and carry secreted molecules(1,2). In the adult and older embryo, the majority of CSF is made by the choroid plexus, a series of highly vascularized secretory regions located adjacent to the brain ventricles(3-5). In zebrafish, the choroid plexus is fully formed at 144 hours post fertilization (hpf)(6). Prior to this, in both zebrafish and other vertebrate embryos including mouse, a significant amount of embryonic CSF (eCSF) is present . These data and studies in chick suggest that the neuroepithelium is secretory early in development and may be the major source of eCSF prior to choroid plexus development(7). eCSF contains about three times more protein than adult CSF, suggesting that it may have an important role during development(8,9). Studies in chick and mouse demonstrate that secreted factors in the eCSF, fluid pressure, or a combination of these, are important for neurogenesis, gene expression, cell proliferation, and cell survival in the neuroepithelium(10-20). Proteomic analyses of human, rat, mouse, and chick eCSF have identified many proteins that may be necessary for CSF function. These include extracellular matrix components, apolipoproteins, osmotic pressure regulating proteins, and proteins involved in cell death and proliferation(21-24). However, the complex functions of the eCSF are largely unknown. We have developed a method for removing eCSF from zebrafish brain ventricles, thus allowing for identification of eCSF components and for analysis of the eCSF requirement during development. Although more eCSF can be collected from other vertebrate systems with larger embryos, eCSF can be collected from the earliest stages of zebrafish development, and under genetic or environmental conditions that lead to abnormal brain ventricle volume or morphology. Removal and collection of eCSF allows for mass spectrometric analysis, investigation of eCSF function, and reintroduction of select factors into the ventricles to assay their function. Thus the accessibility of the early zebrafish embryo allows for detailed analysis of eCSF function during development.

Frontiers in research on maternal diabetes-induced neural tube defects: Past, present and future

Diabetes mellitus rightly regarded as a silent-epidemic is continually on the rise and estimated to have a global prevalence of 6.4 % as of 2010. Diabetes during pregnancy is a well known risk factor for congenital anomalies in various organ systems that contribute to neonatal mortality, including cardiovascular, gastrointestinal, genitourinary and neurological systems, among which the neural tube defects are frequently reported. Over the last two to three decades, several groups around the world have focussed on identifying the molecular cues and cellular changes resulting in altered gene expression and the morphological defects and in diabetic pregnancy. In recent years, the focus has gradually shifted to looking at pre-programmed changes and activation of epigenetic mechanisms that cause altered gene expression. While several theories such as oxidative stress, hypoxia, and apoptosis triggered due to hyperglycemic conditions have been proposed and proven for being the cause for these defects, the exact mechanism or the link between how high glucose can alter gene expression/transcriptome and activate epigenetic mechanisms is largely unknown. Although preconceptual control of diabetes, (i.e., managing glucose levels during pregnancy), and in utero therapies has been proposed as an effective solution for managing diabetes during pregnancy, the impact that a fluctuating glycemic index can have on foetal development has not been evaluated in detail. A tight glycemic control started before pregnancy has shown to reduce the incidence of congenital abnormalities in diabetic mothers. On the other hand, a tight glycemic control after organogenesis and embryogenesis have begun may prove insufficient to prevent or reverse the onset of congenital defects. The importance of determining the extent to which glycemic levels in diabetic mothers should be regulated is critical as foetal hypoglycemia has also been shown to be teratogenic. Finally, the major question remaining is if this whole issue is negligible and not worthy of investigation as the efficient management of diabetes during pregnancy is well in place in many countries.

The path from the choroid plexus to the subventricular zone: go with the flow!

In adult mammals, under physiological conditions, neurogenesis, the process of generating new functional neurons from precursor cells, occurs mainly in two brain areas: the subgranular zone in the dentate gyrus of the hippocampus, and the subventricular zone (SVZ) lining the walls of the brain lateral ventricles. Taking into account the location of the SVZ and the cytoarchitecture of this periventricular neural progenitor cell niche, namely the fact that the slow dividing primary progenitor cells (type B cells) of the SVZ extend an apical primary cilium toward the brain ventricular space which is filled with cerebrospinal fluid (CSF), it becomes likely that the composition of the CSF can modulate both self-renewal, proliferation and differentiation of SVZ neural stem cells. The major site of CSF synthesis is the choroid plexus (CP); quite surprisingly, however, it is still largely unknown the contribution of molecules specifically secreted by the adult CP as modulators of the SVZ adult neurogenesis. This is even more relevant in light of recent evidence showing the ability of the CP to adapt its transcriptome and secretome to various physiologic and pathologic stimuli. By giving particular emphasizes to growth factors and axonal guidance molecules we will illustrate how CP-born molecules might play an important role in the SVZ niche cell population dynamics.

Neurogenesis at the brain-cerebrospinal fluid interface

Cerebral cortical progenitor cells can be classified into several different types, and each progenitor type integrates cell-intrinsic and cell-extrinsic cues to regulate neurogenesis. On one hand, cell-intrinsic mechanisms that depend upon appropriate apical-basal polarity are established by adherens junctions and apical complex proteins and are particularly important in progenitors with apical processes contacting the lateral ventricle. The apical protein complexes themselves are concentrated at the ventricular surface, and apical complex proteins regulate mitotic spindle orientation and cell fate. On the other hand, remarkably little is known about how cell-extrinsic cues signal to progenitors and couple with cell-intrinsic mechanisms to instruct neurogenesis. Recent research shows that the cerebrospinal fluid, which contacts apical progenitors at the ventricular surface and bathes the apical complex of these cells, provides growth- and survival-promoting cues for neural progenitor cells in developing and adult brain. This review addresses how the apical-basal polarity of progenitor cells regulates cell fate and allows progenitors to sample diffusible signals distributed by the cerebrospinal fluid. We also review several classes of signaling factors that the cerebrospinal fluid distributes to the developing brain to instruct neurogenesis.

Cerebrospinal fluid control of neurogenesis induced by retinoic acid during early brain development

Embryonic-cerebrospinal fluid (E-CSF) plays crucial roles in early brain development including the control of neurogenesis. Although FGF2 and lipoproteins present in the E-CSF have previously been shown to be involved in neurogenesis, the main factor triggering this process remains unknown. E-CSF contains all-trans-retinol and retinol-binding protein involved in the synthesis of retinoic acid (RA), a neurogenesis inducer. In early chick embryo brain, only the mesencephalic-rombencephalic isthmus (IsO) is able to synthesize RA. Here we show that in chick embryo brain development: (1) E-CSF helps to control RA synthesis in the IsO by means of the RBP and all-trans-retinol it contains; (2) E-CSF has retinoic acid activity, which suggests it may act as a diffusion pathway for RA; and (3) the influence of E-CSF on embryonic brain neurogenesis is to a large extent due to its involvement in RA synthesis. These data help to understand neurogenesis from neural progenitor cells.

The embryonic blood-CSF barrier has molecular elements to control E-CSF osmolarity during early CNS development

In vertebrates, brain development takes place at the expanded anterior end of the neural tube. After closure of the anterior neuropore, the brain wall forms a physiologically sealed cavity that encloses embryonic cerebrospinal fluid (E-CSF), a complex and protein-rich fluid. E-CSF has several crucial roles in brain anlagen development. In this respect, during the initiation of neurogenesis, increases in the volume of brain cavities account for 70% of the total growth of the brain primordium, and are accompanied by a parallel increase in E-CSF volume. Recently, we reported the presence of several blood vessels located in the brain stem lateral to the ventral midline, at the mesencephalon and prosencephalon level, which have a transient blood-CSF barrier function in chick embryos by transporting proteins in a selective manner via transcellular routes. These blood vessels control E-CSF protein composition and homeostasis during this early stage of CNS development, just after closure of the neuropores. Here we report that in chick and rat embryos these same blood vessels, which lie close to the neuroectoderm, express several molecules related to water and ion transport, namely AQP1, AQP4 and Kir4.1. Our results confirm that a blood-CSF barrier controls E-CSF composition and homeostasis from early stages of brain development in chick embryos, including water and ion influx, thus regulating E-CSF osmolarity. On the basis of our findings, we also propose that a similar blood-CSF barrier is present in mammals at equivalent developmental stages of the brain.

Early embryonic brain development in rats requires the trophic influence of cerebrospinal fluid

Cerebrospinal fluid has shown itself to be an essential brain component during development. This is particularly evident at the earliest stages of development where a lot of research, performed mainly in chick embryos, supports the evidence that cerebrospinal fluid is involved in different mechanisms controlling brain growth and morphogenesis, by exerting a trophic effect on neuroepithelial precursor cells (NPC) involved in controlling the behaviour of these cells. Despite it being known that cerebrospinal fluid in mammals is directly involved in corticogenesis at fetal stages, the influence of cerebrospinal fluid on the activity of NPC at the earliest stages of brain development has not been demonstrated. Here, using "in vitro" organotypic cultures of rat embryo brain neuroepithelium in order to expose NPC to or deprive them of cerebrospinal fluid, we show that the neuroepithelium needs the trophic influence of cerebrospinal fluid to undergo normal rates of cell survival, replication and neurogenesis, suggesting that NPC are not self-sufficient to induce their normal activity. This data shows that cerebrospinal fluid is an essential component in chick and rat early brain development, suggesting that its influence could be constant in higher vertebrates.

Totally tubular: the mystery behind function and origin of the brain ventricular system

A unique feature of the vertebrate brain is the ventricular system, a series of connected cavities which are filled with cerebrospinal fluid (CSF) and surrounded by neuroepithelium. While CSF is critical for both adult brain function and embryonic brain development, neither development nor function of the brain ventricular system is fully understood. In this review, we discuss the mystery of why vertebrate brains have ventricles, and whence they originate. The brain ventricular system develops from the lumen of the neural tube, as the neuroepithelium undergoes morphogenesis. The molecular mechanisms underlying this ontogeny are described. We discuss possible functions of both adult and embryonic brain ventricles, as well as major brain defects that are associated with CSF and brain ventricular abnormalities. We conclude that vertebrates have taken advantage of their neural tube to form the essential brain ventricular system.

Global gene expression analysis of cranial neural tubes in embryos of diabetic mice

Maternal diabetes causes congenital malformations in various organs including the neural tube in fetuses. In this study, we have analyzed the differential gene expression profiling in the cranial neural tube of embryos from diabetic and control mice by using the oligonucleotide microarray. Expression patterns of genes and proteins that are differentially expressed in the cranial neural tube were further examined by the real-time reverse transcriptase-polymerase chain reaction, in situ hybridization, and immunohistochemistry. Proliferation index and apoptosis were examined by BrdU (5-bromo-2-deoxyuridine) labeling and TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) assay, respectively. Embryos (E11.5) of diabetic pregnancies displayed distortion in neuroepithelia of the cranial neural tube. Microarray analysis revealed that a total of 390 genes exhibited more than twofold changes in expression level in the cranial neural tube of embryos from diabetic mice. Several genes involving apoptosis, proliferation, migration, and differentiation of neurons in the cranial neural tube were differentially expressed in embryos of diabetic pregnancy. In addition, maternal diabetes perturbed the development of choroid plexus and ventricular systems and reduced the production of proteins such as Ttr and Igf2 in the developing brain, indicating that these changes could impair the survival and proliferation of neuroepithelial cells and neurogenesis in embryos of diabetic mice. It is concluded that altered expression of a variety of genes involved in brain development is associated with cranial neural tube dysmorphogenesis that may subsequently contribute to intellectual impairment of the offspring of a diabetic mother.

Why the embryo still matters: CSF and the neuroepithelium as interdependent regulators of embryonic brain growth, morphogenesis and histiogenesis

The key focus of this review is that both the neuroepithelium and embryonic cerebrospinal fluid (CSF) work in an integrated way to promote embryonic brain growth, morphogenesis and histiogenesis. The CSF generates pressure and also contains many biologically powerful trophic factors; both play key roles in early brain development. Accumulation of fluid via an osmotic gradient creates pressure that promotes rapid expansion of the early brain in a developmental regulated way, since the rates of growth differ between the vesicles and for different species. The neuroepithelium and ventricles both contribute to this growth but by different and coordinated mechanisms. The neuroepithelium grows primarily by cell proliferation and at the same time the ventricle expands via hydrostatic pressure generated by active transport of Na(+) and transport or secretion of proteins and proteoglycans that create an osmotic gradient which contribute to the accumulation of fluid inside the sealed brain cavity. Recent evidence shows that the CSF regulates relevant aspects of neuroepithelial behavior such as cell survival, replication and neurogenesis by means of growth factors and morphogens. Here we try to highlight that early brain development requires the coordinated interplay of the CSF contained in the brain cavity with the surrounding neuroepithelium. The information presented is essential in order to understand the earliest phases of brain development and also how neuronal precursor behavior is regulated.

All-trans retinol and retinol-binding protein from embryonic cerebrospinal fluid exhibit dynamic behaviour during early central nervous system development

Embryonic cerebrospinal fluid (E-CSF) is involved in the regulation of survival, proliferation and neurogenesis of neuroectodermal progenitor cells, as well as in the control of mesencephalic gene expression in collaboration with the isthmic organizer. Recently, we showed the presence of retinol-binding protein (RBP) within the E-CSF proteome. RBP is an all-trans retinol carrier, a molecule that can be metabolized into retinoic acid, a morphogen involved in central nervous system (CNS) morphogenesis and patterning. Here we demonstrate the presence of all-trans retinol within the E-CSF and analyse the dynamics of RBP and all-trans retinol within this fluid, as well as the expression of retinoic acid-synthesizing enzymes during early CNS development. Our results suggest a relationship between the dynamics of these molecules and the early events of CNS patterning.

Region-specific requirement for cholesterol modification of sonic hedgehog in patterning the telencephalon and spinal cord

Sonic hedgehog (Shh) secreted from the axial signaling centers of the notochord and prechordal plate functions as a morphogen in dorsoventral patterning of the neural tube. Active Shh is uniquely cholesterol-modified and the hydrophobic nature of cholesterol suggests that it might regulate Shh spreading in the neural tube. Here, we examined the capacity of Shh lacking the cholesterol moiety (ShhN) to pattern different cell types in the telencephalon and spinal cord. In mice expressing ShhN, we detected low-level ShhN in the prechordal plate and notochord, consistent with the notion that ShhN can rapidly spread from its site of synthesis. Surprisingly, we found that low-level ShhN can elicit the generation of a full spectrum of ventral cell types in the spinal cord, whereas ventral neuronal specification and ganglionic eminence development in the Shh(N/-) telencephalon were severely impaired, suggesting that telencephalic patterning is more sensitive to alterations in local Shh concentration and spreading. In agreement, we observed induction of Shh pathway activity and expression of ventral markers at ectopic sites in the dorsal telencephalon indicative of long-range ShhN activity. Our findings indicate an essential role for the cholesterol moiety in restricting Shh dilution and deregulated spread for patterning the telencephalon. We propose that the differential effect of ShhN in patterning the spinal cord versus telencephalon may be attributed to regional differences in the maintenance of Shh expression in the ventral neuroepithelium and differences in dorsal tissue responsiveness to deregulated Shh spreading behavior.

The particles of the embryonic cerebrospinal fluid: how could they influence brain development?

During brain development, the embryonic cerebrospinal fluid (E-CSF) allows brain expansion and promotes neuroepithelial cell survival, proliferation or differentiation. Previous analyses of E-CSF content have revealed a high protein concentration and the presence of membranous particles. The role of these particles in the E-CSF remains poorly investigated. In this study we showed that the E-CSF contains at least two pools of particles: lipoproteins and exosome-like particles. We showed that these two populations of particles strongly interact with neuropithelial cells via an endocytic process, which display regional specificity along the developing neural tube. Finally, we explore and discuss the possibility that these interactions may influence brain development through the regulation of morphogen and growth factor signaling transduction.

FGF2 plays a key role in embryonic cerebrospinal fluid trophic properties over chick embryo neuroepithelial stem cells

During early stages of brain development, neuroepithelial stem cells undergo intense proliferation as neurogenesis begins. Fibroblast growth factor 2 (FGF2) has been involved in the regulation of these processes, and although it has been suggested that they work in an autocrine-paracrine mode, there is no general agreement on this because the behavior of neuroepithelial cells is not self-sufficient in explants cultured in vitro. In this work, we show that during early stages of development in chick embryos there is another source of FGF2, besides that of the neuroepithelium, which affects the brain primordium, since the cerebrospinal fluid (E-CSF) contains several isoforms of this factor. We also demonstrate, both in vitro and in vivo, that the FGF2 from the E-CSF has an effect on the regulation of neuroepithelial cell behavior, including cell proliferation and neurogenesis. In order to clarify putative sources of FGF2 in embryonic tissues, we detected by in situ hybridization high levels of mRNA expression in notochord, mesonephros and hepatic primordia, and low levels in brain neuroectoderm, corroborated by semiquantitative PCR analysis. Furthermore, we show that the notochord segregates several FGF2 isoforms which modify the behavior of the neuroepithelial cells in vitro. In addition, we show that the FGF2 ligand is present in the embryonic serum; and, by means of labeled FGF2, we prove that this factor passes via the neuroepithelium from the embryonic serum to the E-CSF in vivo. Considering all these results, we propose that, in chick embryos, the behavior of brain neuroepithelial stem cells at the earliest stages of development is influenced by the action of the FGF2 contained within the E-CSF which could have an extraneural origin, thus suggesting a new and complementary way of regulating brain development.