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Schemata of formation of the choroid plexus of IV ventricle in zebrafish as revealed by analysis of different transgenics. Above– mn16Et, below – Gateways. The cytosolic GFP, first detected the lateral clusters, could be detected in the prospective epithelial cells of mn16Et at 3 dpf, i.e., after these coalesced toward the midline. This mimics events of the CP morphogenesis as hypothesized in mammals. In contrast, in the Gateway transgenics, the GFP is rather prominent in the midline cluster prior to its coalescence, i.e. during a stage of tela choroidea. Abbreviations: E, epidermal cells of the prospective choroid plexus of IV ventricle; G, glial cells of the prospective choroid plexus of IV ventricle; M, midline cluster; RL, rhombic lips; URL, upper rhombic lips.
Source publication
The blood-cerebrospinal fluid boundary is present at the level of epithelial cells of the choroid plexus. As one of the sources of the cerebrospinal fluid (CSF), the choroid plexus (CP) plays an important role during brain development and function. Its formation has been studied largely in mammalian species. Lately, progress in other model animals,...
Citations
... While the analysed articles contained both keywords CP and TC, none of them specifically addressed the difference between these structures or the use of the terms. We are aware that a number of relevant publications might have been overlooked, if the CP and TC did not occur in title, keywords or abstract [e.g., 12,79]. The search was limited as described to compare the respective author's notion of both terms, even if no actual definitions were given. ...
... Their high permeability allows diffusion based delivery by soaking them in neurotoxin containing solution 80,85 , and a lack of a blood brain barrier (BBB)/Blood -Cerebral Spinal Fluid Barrier until 7 days post fertilization (dpf) allows central nervous system access for otherwise impermeable compounds 86 . Lastly, zebrafish larvae have homologous mDA regions for Parkinson's disease modeling as early as 2 dpf 83,87 . This allows for a theoretical five-day window for the introduction of compounds that cannot enter the brain typically through soaking of the Zebrafish larvae in solution. ...
... The discrepancy between a 3dpf and 4 dpf treatment starting point for 6-OHDA exposure is possibly a result of blood brain barrier (BBB) development and its selectivity/ impermeability increasing with age 86 . The BBB becomes largely impermeable at 5 dpf and finished choroid plexus formation at 7 dpf securing the Blood-CSF barrier 87,111 . Previous work has shown that 6-OHDA does not cross the BBB as readily as other neurotoxins associated with PD. ...
Parkinsons’ disease (PD) is a neurodegenerative disorder characterized by the loss of midbrain dopaminergic (mDA) neurons that currently has no cure. It is primarily characterized in patients by motor symptoms that include but are not limited to: tremor at rest, rigidity, akinesia, and postural instability affecting the quality of life for over 8.5 million people worldwide. The neurotoxin 6-hydroxydopamine (6-OHDA) has been used to induce a Parkinson’s disease-like state in several animal models; however, assessment of 6-OHDA use in zebrafish demonstrated a lack of consensus on method and utility. We determined an optimized protocol utilizing 6-OHDA to produce a PD-like state as defined by a significant reduction of tyrosine hydroxylase (th1). Additionally, we found the mechanism of action for 6-OHDA toxicity to be conserved as defined by the upregulation vii of super oxide dismutase sod1 and sod2, and down regulation of mitochondrial dysfunction indicator pink1.
... The elevated ICP therefore does not appear to associate with sleep, but rather dictated by the circadian rhythm. This retained circadian pattern may stem from the highly conserved choroid plexus originating from a common ancestor with a predicted diurnal activity preference [52]. With the reversibility of sleep rhythms, these may well have been modulated to fit with the environmental predation risk, as species evolved [53][54][55]. ...
Background
It is crucial to maintain the intracranial pressure (ICP) within the physiological range to ensure proper brain function. The ICP may fluctuate during the light-dark phase cycle, complicating diagnosis and treatment choice in patients with pressure-related disorders. Such ICP fluctuations may originate in circadian or sleep-wake cycle-mediated modulation of cerebrospinal fluid (CSF) flow dynamics, which in addition could support diurnal regulation of brain waste clearance.
Methods
ICP was monitored continuously in patients who underwent placement of an external ventricular drain (EVD) and by telemetric monitoring in experimental rats. CSF was collected via the EVD in patients and the rodent CSF secretion rate determined by in vivo experimentation. Rodent choroid plexus transporter transcripts were quantified with RNAseq and transport activity with ex vivo isotope transport assays.
Results
We demonstrated that ICP increases by 30% in the dark phase in both species, independently of vascular parameters. This increase aligns with elevated CSF collection in patients (12%) and CSF production rate in rats (20%), the latter obtained with the ventriculo-cisternal perfusion assay. The dark-phase increase in CSF secretion in rats was, in part, assigned to increased transport activity of the choroid plexus Na⁺,K⁺,2Cl⁻ cotransporter (NKCC1), which is implicated in CSF secretion by this tissue.
Conclusion
CSF secretion, and thus ICP, increases in the dark phase in humans and rats, irrespective of their diurnal/nocturnal activity preference, in part due to altered choroid plexus transport activity in the rat. Our findings suggest that CSF dynamics are modulated by the circadian rhythm, rather than merely sleep itself.
... 127 The evolutionarily conserved Notch and Shh signaling pathways regulate CP development. 4,47,128,129 Gli3 is one of the downstream genes in Shh signaling. CPIII fails to develop in Gli3-deficient mouse embryos. ...
... 128 These studies raised questions about the fate of the midline field of the HRPE, the contribution of the HRPE to CPIV vasculature or stroma, the presence of a roof plate at the CPIV level, the genes involved in the specification of different cell lineages in CPIV, and cell adhesion in this CP. 4,152 It seems that spacial segregation of the medial and lateral fields determines the CP cell lineages. Zebrafish studies have clarified the role of the HRPE midline field. ...
The brain ventricular system (BVS) consists of the brain ventricles and channels filled with cerebrospinal fluid (CSF). Disturbance of CSF flow has been linked to neurodegenerative diseases including hydrocephalus, which manifests as an expansion of the BVS. These relatively common developmental disorders have been observed in humans and domesticated animals and linked to functional deficiency of the choroid plexus (CP) or ependymal cells that generate CSF, or the motile cilia that drive CSF flow. Vertebrates with horizontal body posture have ancient evolutionary adaptations to assist CSF flow such as the Reissner fiber, lost in human adults upon transition to bipedal locomotion. The underlying causes of hydrocephalus and related diseases such as scoliosis could be elucidated through several recently-developed animal models including rodents (mice, rats, hamsters) and zebrafish.
Owing to their horizontal body posture and the way that gravity affects their CSF flow, the mammalian models differ significantly from humans. In contrast, the fish swim against the current and experience the forward-to-backward mechanical force analogous to that caused by gravity in humans. On the other side of the spectrum of BVS anomalies, there is “slit-ventricle” syndrome (microcephaly), which develops due to insufficient inflation of the BVS. Recent advances in the functional genetics of zebrafish revealed novel genetic elements in the development of the BVS and the CSF circulation.
The aim of this review is to reveal the common elements among the morphologically different BVSs of zebrafish, a typical representative of teleosts, and vertebrates in general, and to illustrate the features of the zebrafish model useful for studies of the BVS, choroid plexus (CP), and CSF flow. The molecular elements of the putative developmental mechanism will be discussed.
... From there, two apertures (Luschka and Magendie) drain the CSF to the subarachnoid space and the spinal cord central canal. Each of the four brain ventricles contains a CP (Bill & Korzh, 2014;Mogi et al., 2012;Wilting & Christ, 1989). ...
... including the third and fourth ventricle CPs (CPIII and CPIV) (Bill et al., 2008;Bill & Korzh, 2014;García-Lecea et al., 2008), PIN (Masai et al., 1997), PP (Concha & Wilson, 2001), NH and ME (Bassi et al., 2016), SCO (Fernández-Llebrez et al., 2001), and AP (Ma, 1997). ...
... It contains a CP, PIN-PP complex, SCO and ME (Bill et al., 2008;Bill & Korzh, 2014;García-Lecea et al., 2008. Therefore, it probably corresponds to the third ventricle in mammals. ...
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.
... The copyright holder for this preprint this version posted December 9, 2022. ; https://doi.org/10.1101/2022.12.08.519692 doi: bioRxiv preprint allowed us to simultaneously visualize brain vasculature and two anatomically separate CPs, the diencephalic and myelencephalic CP (dCP and mCP) that are equivalent to the 3rd and 4th ventricular CP in mammals, respectively (Fig. 1a, 1a') [15][16][17] . Zebrafish larvae carrying double transgenic Tg(plvap:EGFP);Tg(glut1b:mCherry) reporters, which mark fenestrated endothelial cells in EGFP and BBB endothelium in mCherry, enabled us to map transcriptionally heterogeneous networks of brain and meningeal vasculature at 120 hours post fertilization (hpf) (Fig. 1b,1b'): Specifically, 1) blood vessels exhibiting high levels of Tg(plvap:EGFP), but low levels of Tg(glut1b:mCherry), expression; ...
... We next sought to explore angiogenic cues responsible for vessel development in the fenestrated brain vascular beds, which is independent of Wnt/β-catenin signaling. Previous studies, including our recent work, characterized the vascularization processes of the mCP 12,15,17 , however, no angiogenic cues have (which was not certified by peer review) is the author/funder. All rights reserved. ...
Fenestrated and blood-brain barrier (BBB)-forming endothelia constitute major brain capillaries that mediate blood-brain communications crucial for brain homeostasis. How these capillary types emerge in a brain region-specific manner remains unknown. Here we performed a comparative analysis of the zebrafish choroid plexuses (CPs) and circumventricular organs (CVOs), and show common angiogenic mechanisms for fenestrated brain capillary development. We found that zebrafish deficient for Gpr124, Reck, or Wnt7aa exhibit severely-impaired BBB angiogenesis without apparent defects in fenestrated capillary formation in the CPs and CVOs, demonstrating vessel-type-selective vascularization mechanisms. Conversely, simultaneous losses of various Vegf combinations revealed remarkable heterogeneity of endothelial requirements for Vegfs-dependent angiogenesis within and across these organs. Expression analysis suggests that endothelial cells and non-neuronal cell types uniquely present in the CPs and CVOs are major sources of Vegfs. Comparative analysis further uncovered unexpected, significant interplay of Vegfc/d and Vegfa in fenestrated vessel formation across the brain. These results identified brain-region-specific presentations and interplay of Vegfs underlying fenestrated capillary development.
TEASER
Identification of novel and complex molecular interplay critical for directing permeable vascular formation across the brain
... Multiciliated ChP and ependymal cells are well conserved among vertebrates (Bill and Korzh, 2014;Fame et al., 2020), and the Gmnc-dependent multiciliation regulatory network is also shared by vertebrates (Defosset et al., 2021), suggesting their coevolution. By contrast, CRs have not been described beyond amniotes so far, suggesting they represent a relatively recent evolutionary innovation. ...
Cajal-Retzius (CR) neurons are key players of cortical development that display a very unique transcriptomic identity. However, little is known about the mechanisms involved in their fate specification. Here we use scRNAseq to reconstruct the differentiation trajectory of hem-derived CR cells (CRs) and unravel the transient expression of a complete gene module previously known to control the cellular process of multiciliogenesis. However, we find that CRs do not undergo centriole amplification or multiciliation. We show that upon genetic disruption of Gmnc, the master regulator of the multiciliation cascade, CRs are initially produced but fail to reach their normal identity and lean towards an aberrant fate resulting in their massive apoptosis. We further dissect the contribution of multiciliation effector genes and identify Trp73 as a key determinant. Finally, we use in utero electroporation to demonstrate that the intrinsic competence of hem progenitors as well as the heterochronic expression of Gmnc prevent centriole amplification in the CR lineage. Our work exemplifies how the co-option of a complete gene module, repurposed to control a completely distinct process, may contribute to the emergence of novel cell identities.
... The vascular unit of the choroid plexus and its associated vascular barrier resides in the deepest layer of the pia mater and is formed by a complex network of fenestrated capillaries, which allow the selective passage of bioactive molecules coming from the systemic blood circulation [103][104][105]. The choroid plexus represents the interface between the blood and the cerebrospinal fluid (CSF), and it can act as a gatekeeper in the nutritional, metabolic, and hormonal balance, as well as in immune surveillance and trafficking [106]. ...
The vasculature plays an essential role in the development and maintenance of blood-tissue interface homeostasis. Knowledge on the morphological and functional nature of the blood vessels in every single tissue is, however, very poor, but it is becoming clear that each organ is characterized by the presence of endothelial barriers with different properties fundamental for the maintenance of tissue resident immune homeostasis and for the recruitment of blood-trafficking immune cells. The tissue specificity of the vascular unit is dependent on the presence of differentiated endothelial cells that form continues, fenestrated, or sinusoidal vessels with different grades of permeability and different immune receptors, according to how that particular tissue needs to be protected. The gut-brain axis highlights the prominent role that the vasculature plays in allowing a direct and prompt exchange of molecules between the gut, across the gut vascular barrier (GVB), and the brain. Recently, we identified a new choroid plexus vascular barrier (PVB) which receives and integrates information coming from the gut and is fundamental in the modulation of the gut-brain axis. Several pathologies are linked to functional dysregulation of either the gut or the choroid plexus vascular barriers. In this review, we unveil the structural and functional analogies between the GVB and PVB, comparing their peculiar features and highlighting the functional role of pitcher and catcher of the gut-brain axis, including their role in the establishment of immune homeostasis and response upon systemic stimuli. We propose that when the gut vascular barrier—the main protecting system of the body from the external world—is compromised, the choroid plexus gatekeeper becomes a second barrier that protects the central nervous system from systemic inflammation.
... Circumventricular organs (CVO) are structures involved in several vital functions, including the regulation of temperature, body fluids, energy balance, nociception, and the detection of toxic compounds (Korzh and Kondrychyn, 2020). For decades there has been a debate about the possibility of including the CP as a CVO due to the presence of fenestrated capillaries, wide perivascular spaces, and highly specialized ependymal cells (Weindl, 1973;Gross and Weindl, 1987;Bill and Korzh, 2014). Other common characteristics of the CP and CVOs are the peripheral location of brain tissue in proximity to the ventricles, high vascularization, and the production of proteins released into the cerebrospinal fluid (CSF) (Stolp and Molnár, 2015;Richardson et al., 2015). ...
... al, 2005;Zappaterra and Lehtinen, 2012;Lehtinen et. al, 2013;Bill and Korzh, 2014;Saunders et al., 2015). The ultrastructural observation in A. mexicanum suggested that the paraphysis participates in the detoxification of the CSF. ...
Intraventricular and extraventricular choroid plexuses are neuroepithelial folds which arise from the roof of the diencephalon. We describe the circumventricular structure of the diencephalon roof (paraphysis cerebri) during the various development stages of Ambystoma mexicanum. The parasagittal sections of the larvae epithalamus exhibit the presence, in addition to the epiphysis, of two dorsal primordia in nearby areas, which appear to be extraventricular saccular evaginations of different origin that give rise to two structures we define as the anterior extraventricular choroid plexus (AEP) and posterior extraventricular choroid plexus (PEP). During larvae development, the primordia arise perpendicular to each other, grow and show luminal folds and invaginations. Later, the two extraventricular evaginations, which are separate units, become interrelated. As the PEP grows, it covers the AEP dorsally, but it is difficult to define the borders of these organs. AEP is formed by alveolar-acinar epithelial aggregates with evidence of secretion-like content. PEP structure is like a choroid plexus, but its position is extraventricular and dorsal to the AEP. The PEP is always between the AEP and the meninges and can be small or large in size. This means that in A. mexicanum, the paraphysis cerebri is made up of two adjacent organs, which arise almost simultaneously from two different primordia (the AEP and the PEP) and as the posterior one grows, it overlaps the anterior one and masks itself. In conclusion, we suggest that AEP and PEP are homologous to paraphysis cerebri and the dorsal sac, respectively.
... Thus, non-invasive in vivo live imaging is relatively straight-forward, making it possible to observe ChP development [43]. Early studies reported enhancer trap transgenic lines that express GFP in the zebrafish ChP [43][44][45], enabling the study of signaling molecules during development. One of these lines, the Et(cp:EGFP) sj2 line, which expresses GFP under the control of the epithelia-specific keratin4 promoter, results in targeted GFP expression in diencephalic and myelencephalic ChP epithelial cells that correspond to 3V and 4V ChP in the mammalian brain, respectively. ...
Choroid plexus (ChP) epithelial cells are crucial for the function of the blood-cerebrospinal fluid barrier (BCSFB) in the developing and mature brain. The ChP is considered the primary source and regulator of CSF, secreting many important factors that nourish the brain. It also performs CSF clearance functions including removing Amyloid beta and potassium. As such, the ChP is a promising target for gene and drug therapy for neurodevelopmental and neurological disorders in the central nervous system (CNS). This review describes the current successful and emerging experimental approaches for targeting ChP epithelial cells. We highlight methodological strategies to specifically target these cells for gain or loss of function in vivo. We cover both genetic models and viral gene delivery systems. Additionally, several lines of reporters to access the ChP epithelia are reviewed. Finally, we discuss exciting new approaches, such as chemical activation and transplantation of engineered ChP epithelial cells. We elaborate on fundamental functions of the ChP in secretion and clearance and outline experimental approaches paving the way to clinical applications.
