Search

SNCAIP duplication may promote Group 4 medulloblastoma via induction of PRDM6, a poorly characterized member of the PRDF1 and RIZ1 homology domain-containing (PRDM) family of transcription factors. Here, we investigated the function of PRDM6 in human hindbrain neuroepithelial stem cells and tested PRDM6 as a driver of Group 4 medulloblastoma. We report that human PRDM6 localizes predominantly to the nucleus, where it causes widespread repression of chromatin accessibility and complex alterations of gene expression patterns. Genome-wide mapping of PRDM6 binding reveals that PRDM6 binds to chromatin regions marked by histone H3 lysine 27 trimethylation that are located within, or proximal to, genes. Moreover, we show that PRDM6 expression in neuroepithelial stem cells promotes medulloblastoma. Surprisingly, medulloblastomas derived from PRDM6-expressing neuroepithelial stem cells match human Group 3, but not Group 4, medulloblastoma. We conclude that PRDM6 expression has oncogenic potential but is insufficient to drive Group 4 medulloblastoma from neuroepithelial stem cells. We propose that both PRDM6 and additional factors, such as specific cell-of-origin features, are required for Group 4 medulloblastoma. Given the lack of PRDM6 expression in normal tissues and its oncogenic potential shown here, we suggest that PRDM6 inhibition may have therapeutic value in PRDM6-expressing medulloblastomas.

In this review, we explore the inconsistencies in the data and gaps in our knowledge that exist in what is currently known regarding gill chemosensors which drive the cardiorespiratory reflexes in fish. Although putative serotonergic neuroepithelial cells (NEC) dominate the literature, it is clear that other neurotransmitters are involved (adrenaline, noradrenaline, acetylcholine, purines, and dopamine). And although we assume that these agents act on neurons synapsing with the NECs or in the afferent or efferent limbs of the paths between chemosensors and central integration sites, this process remains elusive and may explain current discrepancies or species differences in the literature. To date it has been impossible to link the distribution of NECs to species sensitivity to different stimuli or fish lifestyles and while the gills have been shown to be the primary sensing site for respiratory gases, the location (gills, oro-branchial cavity or elsewhere) and orientation (external/water or internal/blood sensing) of the NECs are highly variable between species of water and air breathing fish. Much of what has been described so far comes from studies of hypoxic responses in fish, however, changes in CO2, ammonia and lactate have all been shown to elicit cardio-respiratory responses and all have been suggested to arise from stimulation of gill NECs. Our view of the role of NECs is broadening as we begin to understand the polymodal nature of these cells. We begin by presenting the fundamental picture of gill chemosensing that has developed, followed by some key unanswered questions about gill chemosensing in general. [ABSTRACT FROM AUTHOR]

The fish gill is a multifunctional organ that is important in multiple physiological processes such as gas transfer, ionoregulation, and chemoreception. This characteristic organ of fishes has received much attention, yet an often-overlooked point is that larval fishes in most cases do not have a fully developed gill, and thus larval gills do not function identically as adult gills. In addition, large changes associated with gas exchange and ionoregulation happen in gills during the larval phase, leading to the oxygen and ionoregulatory hypotheses examining the environmental constraint that resulted in the evolution of gills. This review thus focuses exclusively on the larval fish gill of teleosts, summarizing the development of teleost larval fish gills and its function in gas transfer, ionoregulation, and chemoreception, and comparing and contrasting it to adult gills where applicable, while providing some insight into the oxygen vs ionoregulatory hypotheses debate. [ABSTRACT FROM AUTHOR]

The number of neural stemcells reflects the total number of neurons in the mature brain. As neural stem cells arise from neuroepithelial cells, the neuroepithelial cell population must be expanded to secure a sufficient number of neural stem cells. However, molecular mechanisms that regulate timely differentiation from neuroepithelial to neural stem cells are largely unclear. Here, we show that TCF4/Daughterless is a key factor that determines the timing of the differentiation in Drosophila. The neuroepithelial cells initiated but never completed the differentiation in the absence of TCF4/Daughterless. We also found that TCF4/Daughterless binds to the Notch locus, suggesting that Notch is one of its downstream candidate genes. Consistently, Notch expression was ectopically induced in the absence of TCF4/Daughterless. Furthermore, ectopic activation of Notch signaling phenocopied loss of TCF4/Daughterless. Our findings demonstrate that TCF4/Daughterless directly inactivates Notch signaling pathway, resulting in completion of the differentiation from neuroepithelial cells into neural stem cells with optimal timing. Thus, the present results suggest that TCF4/Daughterless is essential for determining whether to move to the next state or stay in the current state in differentiating neuroepithelial cells. [ABSTRACT FROM AUTHOR]

Background: Similar to induced pluripotent cells (iPSCs), induced neural stem cells (iNSCs) can be directly converted from human somatic cells such as dermal fibroblasts and peripheral blood monocytes. While previous studies have demonstrated the resemblance of iNSCs to neural stem cells derived from primary sources and embryonic stem cells, respectively, a comprehensive analysis of the correlation between iNSCs and their physiological counterparts remained to be investigated. Methods: Nowadays, single-cell sequencing technologies provide unique opportunities for in-depth cellular benchmarking of complex cell populations. Our study involves the comprehensive profiling of converted human iNSCs at a single-cell transcriptomic level, alongside conventional methods, like flow cytometry and immunofluorescence stainings. Results: Our results show that the iNSC conversion yields a homogeneous cell population expressing bona fide neural stem cell markers. Extracting transcriptomic signatures from published single cell transcriptomic atlas data and comparison to the iNSC transcriptome reveals resemblance to embryonic neuroepithelial cells of early neurodevelopmental stages observed in vivo at 5 weeks of development. Conclusion: Our data underscore the physiological relevance of directly converted iNSCs, making them a valuable in vitro system for modeling human central nervous system development and establishing translational applications in cell therapy and compound screening. [ABSTRACT FROM AUTHOR]

Studying the properties of neural stem progenitor cells (NSPCs) in a fish model will provide new information about the organization of neurogenic niches containing embryonic and adult neural stem cells, reflecting their development, origin cell lines and proliferative dynamics. Currently, the molecular signatures of these populations in homeostasis and repair in the vertebrate forebrain are being intensively studied. Outside the telencephalon, the regenerative plasticity of NSPCs and their biological significance have not yet been practically studied. The impressive capacity of juvenile salmon to regenerate brain suggests that most NSPCs are likely multipotent, as they are capable of replacing virtually all cell lineages lost during injury, including neuroepithelial cells, radial glia, oligodendrocytes, and neurons. However, the unique regenerative profile of individual cell phenotypes in the diverse niches of brain stem cells remains unclear. Various types of neuronal precursors, as previously shown, are contained in sufficient numbers in different parts of the brain in juvenile Pacific salmon. This review article aims to provide an update on NSPCs in the brain of common models of zebrafish and other fish species, including Pacific salmon, and the involvement of these cells in homeostatic brain growth as well as reparative processes during the postraumatic period. Additionally, new data are presented on the participation of astrocytic glia in the functioning of neural circuits and animal behavior. Thus, from a molecular aspect, zebrafish radial glia cells are seen to be similar to mammalian astrocytes, and can therefore also be referred to as astroglia. However, a question exists as to if zebrafish astroglia cells interact functionally with neurons, in a similar way to their mammalian counterparts. Future studies of this fish will complement those on rodents and provide important information about the cellular and physiological processes underlying astroglial function that modulate neural activity and behavior in animals. [ABSTRACT FROM AUTHOR]

In adult fish, neurogenesis occurs in many areas of the brain, including the cerebellum, with the ratio of newly formed cells relative to the total number of brain cells being several orders of magnitude greater than in mammals. Our study aimed to compare the expressions of aromatase B (AroB), glutamine synthetase (GS), and cystathionine-beta-synthase (CBS) in the cerebellum of intact juvenile chum salmon, Oncorhynchus keta. To identify the dynamics that determine the involvement of AroB, GS, and CBS in the cellular mechanisms of regeneration, we performed a comprehensive assessment of the expressions of these molecular markers during a long-term primary traumatic brain injury (TBI) and after a repeated acute TBI to the cerebellum of O. keta juveniles. As a result, in intact juveniles, weak or moderate expressions of AroB, GS, and CBS were detected in four cell types, including cells of the neuroepithelial type, migrating, and differentiated cells (graphic abstract, A). At 90 days post injury, local hypercellular areas were found in the molecular layer containing moderately labeled AroB+, GS+, and CBS+ cells of the neuroepithelial type and larger AroB+, GS+, and CBS+ cells (possibly analogous to the reactive glia of mammals); patterns of cells migration and neovascularization were also observed. A repeated TBI caused the number of AroB+, GS+, and CBS+ cells to further increase; an increased intensity of immunolabeling was recorded from all cell types (graphic abstract, C). Thus, the results of this study provide a better understanding of adult neurogenesis in teleost fishes, which is expected to clarify the issue of the reactivation of adult neurogenesis in mammalian species. [ABSTRACT FROM AUTHOR]

The human cortex comprises diverse cell types that emerge from an initially uniform neuroepithelium that gives rise to radial glia, the neural stem cells of the cortex. To characterize the earliest stages of human brain development, we performed single-cell RNA-sequencing across regions of the developing human brain, including the telencephalon, diencephalon, midbrain, hindbrain and cerebellum. We identify nine progenitor populations physically proximal to the telencephalon, suggesting more heterogeneity than previously described, including a highly prevalent mesenchymal-like population that disappears once neurogenesis begins. Comparison of human and mouse progenitor populations at corresponding stages identifies two progenitor clusters that are enriched in the early stages of human cortical development. We also find that organoid systems display low fidelity to neuroepithelial and early radial glia cell types, but improve as neurogenesis progresses. Overall, we provide a comprehensive molecular and spatial atlas of early stages of human brain and cortical development.

Coordinated spatio-temporal regulation of the determination and differentiation of neural stem cells is essential for brain development. Failure to integrate multiple factors leads to defective brain structures or tumour formation. Previous studies suggest changes of chromatin state are needed to direct neural stem cell differentiation, but the mechanisms are unclear. Analysis of Snr1, the Drosophila orthologue of SMARCB1, an ATP-dependent chromatin remodelling protein, identified a key role in regulating the transition of neuroepithelial cells into neural stem cells and subsequent differentiation of neural stem cells into the cells needed to build the brain. Loss of Snr1 in neuroepithelial cells leads to premature neural stem cell formation. Additionally, loss of Snr1 in neural stem cells results in inappropriate perdurance of neural stem cells into adulthood. Snr1 reduction in neuroepithelial or neural stem cells leads to the differential expression of target genes. We find that Snr1 is associated with the actively transcribed chromatin region of these target genes. Thus, Snr1 likely regulates the chromatin state in neuroepithelial cells and maintains chromatin state in neural stem cells for proper brain development. [ABSTRACT FROM AUTHOR]

Human neural stem cell cultures provide progenitor cells that are potential cells of origin for brain cancers. However, the extent to which genetic predisposition to tumor formation can be faithfully captured in stem cell lines is uncertain. Here, we evaluated neuroepithelial stem (NES) cells, representative of cerebellar progenitors. We transduced NES cells with MYCN, observing medulloblastoma upon orthotopic implantation in mice. Significantly, transcriptomes and patterns of DNA methylation from xenograft tumors were globally more representative of human medulloblastoma compared to a MYCN-driven genetically engineered mouse model. Orthotopic transplantation of NES cells generated from Gorlin syndrome patients, who are predisposed to medulloblastoma due to germline-mutated PTCH1, also generated medulloblastoma. We engineered candidate cooperating mutations in Gorlin NES cells, with mutation of DDX3X or loss of GSE1 both accelerating tumorigenesis. These findings demonstrate that human NES cells provide a potent experimental resource for dissecting genetic causation in medulloblastoma.

Coastal marine environments are characterized by daily, seasonal and long-term changes in both O 2 and CO 2 , driven by local biotic and abiotic factors. The neuroepithelial cells (NECs) of fish are thought to be the putative chemoreceptors for sensing oxygen and CO 2 , and, thus, NECs play a key role in detecting these environmental changes. However, the role of NECs as chemosensors in marine fish remains largely understudied. In this study, the NECs of marine threespine sticklebacks (Gasterosteus aculeatus) were characterized using immunohistochemistry. We then determined if there were changes in NEC size and density, and in gill morphology in response to either mild (10 kPa) or moderate (6.8 kPa) hypoxia and two levels of elevated CO 2 (1,500 and 3,000 µatm). We found that the NECs of stickleback contained synaptic vesicles and were innervated, and were 50-300% larger and 2 to 4 times more abundant than in other similar sized freshwater fishes. NEC size and density were largely unaffected by exposure to hypoxia, but there was a 50% decrease in interlamellar cell mass (ILCM) in response to mild and moderate hypoxia. NECs increased in size, but not abundance in response to elevated CO 2 . Moreover, fish exposed to moderate or elevated CO 2 had 53-78% larger ILCMs compared to control fish. Our results demonstrated that adult marine sticklebacks have NECs that can respond to environmentally relevant pCO 2 and likely hypoxia, which highlights the importance of NECs in marine fishes under the heterogeneity of environmental conditions in coastal areas., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The gills are the primary site of exchange in fishes. However, during early life-stages or in amphibious fishes, ionoregulation and gas-exchange may be primarily cutaneous. Given the similarities between larval and amphibious fishes, we hypothesized that cutaneous larval traits are continuously expressed in amphibious fishes across all life-stages to enable the skin to be a major site of exchange on land. Alternatively, we hypothesized that cutaneous larval traits disappear in juvenile stages and are re-expressed in amphibious species in later life-stages. We surveyed six species spanning a range of amphibiousness and characterized cutaneous ionocytes and neuroepithelial cells (NECs) as representative larval skin traits at up to five stages of development. We found that skin ionocyte density remained lower and constant in exclusively water-breathing, relative to amphibious species across development, whereas in amphibious species ionocyte density generally increased. Additionally, adults of the most amphibious species had the highest cutaneous ionocyte densities. Surprisingly, cutaneous NECs were only identified in the skin of one amphibious species (Kryptolebias marmoratus), suggesting that cutaneous NECs are not a ubiquitous larval or amphibious skin trait, at least among the species we studied. Our data broadly supports the continuous-expression hypothesis, as three of four amphibious experimental species expressed cutaneous ionocytes in all examined life-stages. Further, the increasing density of cutaneous ionocytes across development in amphibious species probably facilitates the prolonged occupation of terrestrial habitats. [ABSTRACT FROM AUTHOR]

Although human induced pluripotent stem cells (hiPSCs) hold great potential for the study of human diseases affecting disparate cell types, they have been underutilized in seeking mechanistic insights into the pathogenesis of congenital craniofacial disorders. Craniofrontonasal syndrome (CFNS) is a rare X-linked disorder caused by mutations in EFNB1 and characterized by craniofacial, skeletal, and neurological anomalies. Heterozygous females are more severely affected than hemizygous males, a phenomenon termed cellular interference that involves mosaicism for EPHRIN-B1 function. Although the mechanistic basis for cellular interference in CFNS has been hypothesized to involve Eph/ephrin-mediated cell segregation, no direct evidence for this has been demonstrated. Here, by generating hiPSCs from CFNS patients, we demonstrate that mosaicism for EPHRIN-B1 expression induced by random X inactivation in heterozygous females results in robust cell segregation in human neuroepithelial cells, thus supplying experimental evidence that Eph/ephrin-mediated cell segregation is relevant to pathogenesis in human CFNS patients.

To understand how diverse progenitor cells contribute to human neocortex development, we examined forebrain progenitor behaviour using timelapse imaging. Here we find that cell cycle dynamics of human neuroepithelial (NE) cells differ from radial glial (RG) cells in both primary tissue and in stem cell-derived organoids. NE cells undergoing proliferative, symmetric divisions retract their basal processes, and both daughter cells regrow a new process following cytokinesis. The mitotic retraction of the basal process is recapitulated by NE cells in cerebral organoids generated from human-induced pluripotent stem cells. In contrast, RG cells undergoing vertical cleavage retain their basal fibres throughout mitosis, both in primary tissue and in older organoids. Our findings highlight developmentally regulated changes in mitotic behaviour that may relate to the role of RG cells to provide a stable scaffold for neuronal migration, and suggest that the transition in mitotic dynamics can be studied in organoid models.

When considering what makes us human, the development of the neocortex, the seat of our higher cognitive abilities, is of central importance. Throughout this complex developmental process, neocortical stem and progenitor cells (NSPCs) exert a priming role in determining neocortical tissue fate, through a series of cellular and molecular events. In this Perspective article, we address five questions of relevance for potentially human-specific aspects of NSPCs, (i) Are there human-specific NSPC subtypes? (ii) What is the functional significance of the known temporal differences in NSPC dynamics between human and other great apes? (iii) Are there functional interactions between the human-specific genes preferentially expressed in NSPCs? (iv) Do humans amplify certain metabolic pathways for NSPC proliferation? and finally (v) Have differences evolved during human evolution, notably between modern humans and Neandertals, that affect the performance of key genes operating in NSPCs? We discuss potential implications inherent to these questions, and suggest experimental approaches on how to answer them, hoping to provide incentives to further understand key issues of human cortical development. [ABSTRACT FROM AUTHOR]

When considering what makes us human, the development of the neocortex, the seat of our higher cognitive abilities, is of central importance. Throughout this complex developmental process, neocortical stem and progenitor cells (NSPCs) exert a priming role in determining neocortical tissue fate, through a series of cellular and molecular events. In this Perspective article, we address five questions of relevance for potentially human-specific aspects of NSPCs, (i) Are there human-specific NSPC subtypes? (ii) What is the functional significance of the known temporal differences in NSPC dynamics between human and other great apes? (iii) Are there functional interactions between the human-specific genes preferentially expressed in NSPCs? (iv) Do humans amplify certain metabolic pathways for NSPC proliferation? and finally (v) Have differences evolved during human evolution, notably between modern humans and Neandertals, that affect the performance of key genes operating in NSPCs? We discuss potential implications inherent to these questions, and suggest experimental approaches on how to answer them, hoping to provide incentives to further understand key issues of human cortical development.

Cell segregation is the process by which cells self-organize to establish developmental boundaries, an essential step in tissue formation. Cell segregation is a common outcome of Eph/ephrin signaling, but the mechanisms remain unclear. In craniofrontonasal syndrome, X-linked mosaicism for ephrin-B1 expression has been hypothesized to lead to aberrant Eph/ephrin-mediated cell segregation. Here, we use mouse genetics to exploit mosaicism to study cell segregation in the mammalian embryo and integrate live-cell imaging to examine the underlying cellular and molecular mechanisms. Our data demonstrate that dramatic ephrin-B1-mediated cell segregation occurs in the early neuroepithelium. In contrast to the paradigm that repulsive bidirectional signaling drives cell segregation, unidirectional EphB kinase signaling leads to cell sorting by the Rho kinase-dependent generation of a cortical actin differential between ephrin-B1- and EphB-expressing cells. These results define mechanisms of Eph/ephrin-mediated cell segregation, implicating unidirectional regulation of cortical actomyosin contractility as a key effector of this fundamental process.

The corticospinal tract (CST) is the most important motor system in humans, yet robust regeneration of this projection after spinal cord injury (SCI) has not been accomplished. In murine models of SCI, we report robust corticospinal axon regeneration, functional synapse formation and improved skilled forelimb function after grafting multipotent neural progenitor cells into sites of SCI. Corticospinal regeneration requires grafts to be driven toward caudalized (spinal cord), rather than rostralized, fates. Fully mature caudalized neural grafts also support corticospinal regeneration. Moreover, corticospinal axons can emerge from neural grafts and regenerate beyond the lesion, a process that is potentially related to the attenuation of the glial scar. Rat corticospinal axons also regenerate into human donor grafts of caudal spinal cord identity. Collectively, these findings indicate that spinal cord 'replacement' with homologous neural stem cells enables robust regeneration of the corticospinal projection within and beyond spinal cord lesion sites, achieving a major unmet goal of SCI research and offering new possibilities for clinical translation.

Stroke is a disease of aging. In stroke patients, the enriched group that received stimulating physical, eating, socializing, and group activities resulted in higher activity levels including spending more time on upper limb, communal socializing, listening and iPad activities. While environmental enrichment has been shown to improve the behavioral outcome of stroke in young animals, the effect of an enriched environment on behavioral recuperation and histological markers of cellular proliferation, neuroinflammation, and neurogenesis in old subjects is not known. We used behavioral testing and immunohistochemistry to assess the effect of environment on post-stroke recovery of young and aged rats kept either in isolation or stimulating social, motor, and sensory environment ((+)Env). We provide evidence that post-stroke animals environmental enrichment (+)Env had a significant positive effect on recovery on the rotating pole, the inclined plane, and the labyrinth test. Old age exerted a small but significant effect on lesion size, which was independent of the environment. Further, a smaller infarct volume positively correlated with better recovery of spatial learning based on positive reinforcement, working and reference memory of young, and to a lesser extent, old animals kept in (+)Env. Histologically, isolation/impoverishment was associated with an increased number of proliferating inflammatory cells expressing ED1 cells in the peri-infarcted area of old but not young rats. Further, (+)Env and young age were associated with an increased number of neuroepithelial cells expressing nestin/BrdU as well as beta III tubulin cells in the damaged brain area which correlated with an increased performance on the inclined plane and rotating pole. Finally, (+)Env and an increased number of neurons expressing doublecortin/BrdU cells exerted a significant effect on performance for working memory and performance on the rotating pole in both age groups. A stimulating social, motor and sensory environment had a limited beneficial effect on behavioral recovery (working memory and rotating pole) after stroke in old rats by reducing neuroinflammation and increasing the number of neuronal precursors expressing doublecortin. Old age however, exerted a small but significant effect on lesion size, which was independent of the environment. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is considered as a protective factor against cardiovascular disorders. However, there are few reports on the effects of H2S in the central nervous system during stress or injury. Previous studies on goldfish have shown that astrocytic response occurs in the damaged and contralateral optic nerves. Glial fibrillary acidic protein (GFAP) concentration in the optic nerves of rainbow trout has not been measured previously. This study further characterized the astrocytic response in the optic nerve and the brain of a rainbow trout (Oncorhynchus mykiss) after unilateral eye injury and estimated the amount of H2S-producing enzyme cystathionine β-synthase (CBS) in the brain of the rainbow trout. Within 1 week after unilateral eye injury, a protein band corresponding to a molecular weight of 50 kDa was identified in the ipsi- and contralateral optic nerves of the rainbow trout. The concentration of GFAP in the injured optic nerve increased compared to the protein concentration on the contralateral side. The results of a quantitative analysis of GFAP+ cell distribution in the contralateral optic nerve showed the largest number of GFAP+ cells and fibers in the optic nerve head. In the damaged optic nerve, patterns of GFAP+ cell migration and large GFAP+ bipolar activated astrocytes were detected at 1 week after unilateral eye injury. The study of H2S-producing system after unilateral eye injury in the rainbow trout was conducted using enzyme-linked immunosorbent assay, western blot analysis, and immunohistochemistry of polyclonal antibodies against CBS in the integrative centers of the brain: telencephalon, optic tectum, and cerebellum. Enzyme-linked immunosorbent assay results showed a 1.7-fold increase in CBS expression in the rainbow trout brain at 1 week after unilateral eye injury compared with that in intact animals. In the ventricular and subventricular regions of the rainbow trout telencephalon, CBS+ radial glia and neuroepithelial cells were identified. After unilateral eye injury, the number of CBS+ neuroepithelial cells in the pallial and subpallial periventricular regions of the telencephalon increased. In the optic tectum, unilateral eye injury led to an increase in CBS expression in radial glial cells; simultaneously, the number of CBS+ neuroepithelial cells decreased in intact animals. In the cerebellum of the rainbow trout, neuroglial interrelationships were revealed, where H2S was released, apparently, from astrocyte-like cells. The organization of H2S-producing cell complexes suggests that, the amount of glutamate produced in the rainbow trout cerebellum and its reuptake was controlled by astrocyte-like cells, reducing its excitotoxicity. In the dorsal matrix zone and granular eminences of the rainbow trout cerebellum, CBS was expressed in neuroepithelial cells. After unilateral eye injury, the level of CBS activity increased in all parts of the cerebellum. An increase in the number of H2S-producing cells was a response to oxidative stress after unilateral eye injury, and the overproduction of H2S in the cerebellum occurred to neutralize reactive oxygen species, providing the cells of the rainbow trout cerebellum with a protective effect. A structural reorganization in the dorsal matrix zone, associated with the appearance of an additional CBS+ apical zone, and a decrease in the enzyme activity in the dorsal matrix zone, was revealed in the zones of constitutive neurogenesis. All experiments were approved by the Commission on Biomedical Ethics, A.V. Zhirmunsky National Scientific Center of Marine Biology (NSCMB), Far Eastern Branch, Russian Academy of Science (FEB RAS) (approval No. 1) on July 31, 2019.

Proper development of the O2-sensing system is essential for survival. Here, we characterized the development of the O2-sensing system in the mangrove rivulus (Kryptolebias marmoratus), an amphibious fish that transitions between hypoxic aquatic environments and O2-rich terrestrial environments. We found that NECs formed in the gills and skin of K. marmoratus during embryonic development and that both NEC populations are retained from the embryonic stage to adulthood. We also found that the hyperventilatory response to acute hypoxia was present in embryonic K. marmoratus, indicating that functional O2-sensing pathways are formed during embryonic development. We then exposed embryos to aquatic normoxia, aquatic hyperoxia, aquatic hypoxia, or terrestrial conditions for the first 30 days of embryonic development and tested the hypothesis that environmental O2 availability during embryonic development modulates the development of the O2-sensing system in amphibious fishes. Surprisingly, we found that O2 availability during embryonic development had little impact on the density and morphology of NECs in the gills and skin of K. marmoratus. Collectively, our results demonstrate that, unlike the only other species of fish in which NEC development has been studied to date (i.e., zebrafish), NEC development in K. marmoratus is largely unaffected by environmental O2 levels during the embryonic stage, indicating that there is interspecies variation in O2-induced plasticity in the O2-sensing system of fishes. [ABSTRACT FROM AUTHOR]

In teleost fish, specialized oxygen (O2) chemoreceptors, called neuroepithelial cells (NECs), are found in the gill epithelium in adults. During development, NECs are present in the skin before the formation of functional gills. NECs are known for retaining the monoamine neurotransmitter, serotonin (5-HT) and are conventionally identified through immunoreactivity with antibodies against 5-HT or synaptic vesicle protein (SV2). However, identification of NECs in live tissue and isolated cell preparations has been challenging due to the lack of a specific marker. The present study explored the use of the transgenic zebrafish, ETvmat2:GFP, which expresses green fluorescent protein (GFP) under the control of the vesicular monoamine transporter 2 (vmat2) regulatory element, to identify NECs. Using immunohistochemistry and confocal microscopy, we confirmed that the endogenous GFP in ETvmat2:GFP labelled serotonergic NECs in the skin of larvae and in the gills of adults. NECs of the gill filaments expressed a higher level of endogenous GFP compared with other cells. The endogenous GFP also labelled intrabranchial neurons of the gill filaments. Flow cytometric analysis demonstrated that filamental NECs could be distinguished from other dissociated gill cells based on high GFP expression alone. Acclimation to 2 weeks of severe hypoxia (PO2 = 35 mmHg) induced an increase in filamental NEC frequency, size and GFP gene expression. Here we present for the first time a transgenic tool that labels O2 chemoreceptors in an aquatic vertebrate and its use in high-throughput experimentation. [ABSTRACT FROM AUTHOR]

Studies of the olfactory epithelium model system have demonstrated that production of neurons is regulated by negative feedback. Previously, we showed that a locally produced signal, the TGFβ superfamily ligand GDF11, regulates the genesis of olfactory receptor neurons by inhibiting proliferation of the immediate neuronal precursors (INPs) that give rise to them. GDF11 is antagonized by follistatin (FST), which is also produced locally. Here, we show that Fst(-/-) mice exhibit dramatically decreased neurogenesis, a phenotype that can only be partially explained by increased GDF11 activity. Instead, a second FST-binding factor, activin βB (ACTβB), inhibits neurogenesis by a distinct mechanism: whereas GDF11 inhibits expansion of INPs, ACTβB inhibits expansion of stem and early progenitor cells. We present data supporting the concept that these latter cells, previously considered two distinct types, constitute a dynamic stem/progenitor population in which individual cells alternate expression of Sox2 and/or Ascl1. In addition, we demonstrate that interplay between ACTβB and GDF11 determines whether stem/progenitor cells adopt a glial versus neuronal fate. Altogether, the data indicate that the transition between stem cells and committed progenitors is neither sharp nor irreversible and that GDF11, ACTβB and FST are crucial components of a circuit that controls both total cell number and the ratio of neuronal versus glial cells in this system. Thus, our findings demonstrate a close connection between the signals involved in the control of tissue size and those that regulate the proportions of different cell types.

Long interspersed nuclear elements-1 (LINE-1 or L1s) are abundant retrotransposons that comprise approximately 20% of mammalian genomes. Active L1 retrotransposons can impact the genome in a variety of ways, creating insertions, deletions, new splice sites or gene expression fine-tuning. We have shown previously that L1 retrotransposons are capable of mobilization in neuronal progenitor cells from rodents and humans and evidence of massive L1 insertions was observed in adult brain tissues but not in other somatic tissues. In addition, L1 mobility in the adult hippocampus can be influenced by the environment. The neuronal specificity of somatic L1 retrotransposition in neural progenitors is partially due to the transition of a Sox2/HDAC1 repressor complex to a Wnt-mediated T-cell factor/lymphoid enhancer factor (TCF/LEF) transcriptional activator. The transcriptional switch accompanies chromatin remodelling during neuronal differentiation, allowing a transient stimulation of L1 transcription. The activity of L1 retrotransposons during brain development can have an impact on gene expression and neuronal function, thereby increasing brain-specific genetic mosaicism. Further understanding of the molecular mechanisms that regulate L1 expression should provide new insights into the role of L1 retrotransposition during brain development. Here we show that L1 neuronal transcription and retrotransposition in rodents are increased in the absence of methyl-CpG-binding protein 2 (MeCP2), a protein involved in global DNA methylation and human neurodevelopmental diseases. Using neuronal progenitor cells derived from human induced pluripotent stem cells and human tissues, we revealed that patients with Rett syndrome (RTT), carrying MeCP2 mutations, have increased susceptibility for L1 retrotransposition. Our data demonstrate that L1 retrotransposition can be controlled in a tissue-specific manner and that disease-related genetic mutations can influence the frequency of neuronal L1 retrotransposition. Our findings add a new level of complexity to the molecular events that can lead to neurological disorders.

The balance between proliferation and differentiation of stem cells and progenitors determines the size of an adult brain region. While the molecular mechanisms regulating proliferation and differentiation of cortical progenitors have been intensively studied, an analysis of the kinetics of progenitor choice between self-renewal and differentiation in vivo is, due to the technical difficulties, still unknown. Here we established a descriptive mathematical model to estimate the probability of self-renewal or differentiation of cortical progenitor behaviors in vivo, a variable we have termed the expansion coefficient. We have applied the model, one which depends only on experimentally measured parameters, to the developing mouse cortex where the expansive neuroepithelial cells and neurogenic radial glial progenitors are coexisting. Surprisingly, we found that the expansion coefficients of both neuroepithelium cells and radial glial progenitors follow the same developmental trajectory during cortical development, suggesting a common rule governing selfrenewal/differentiation behaviors in mouse cortical progenitor differentiation. [ABSTRACT FROM AUTHOR]

Impaired gill function is a critical issue in aquaculture due to factors such as poor water quality, disease, and farm management practices which can greatly compromise gill integrity and ultimately fish growth and survival. Regeneration of damaged gill tissue has been reported for some fish species, however, little is known about Atlantic salmon, which is one of the most economically important salmonid species. This study investigated the regenerative capability of gill tissue following resection in post-smolt Atlantic salmon reared in fresh water. Fish were subjected to two levels of resection severity: 30% or 50% of filament length. Changes in filament length and the cytological and functional capacity of regenerated tissue were studied at several time points post-resection (PR). On average, 38% ± 3.89 of the resected filament length regenerated in both resected groups at week-20 PR. However, absolute regeneration (mm) in 50% resected filaments was greater as compared to the 30% resected filaments. In both groups, regeneration percentage was significantly different among individuals, but was not correlated with initial body size, condition factor, or overall fish growth rate. Immunohistochemistry showed an increase in cell proliferation at the filament tip shortly after resection followed by the appearance of ionocytes, chemoreceptive neuroepithelial cells (NECs), and nerve fibres at week-4 PR. In both resected groups >50% and 90% of NECs were innervated by week-12 and -20 PR, respectively. Gill Na+/K+-ATPase activity in regenerated tissue was not significantly different from that of internal control and non-resected control fish. Our results demonstrate significant regeneration and apparent functional recovery of resected gill filaments in Atlantic salmon which has important implications for recovery from gill damage and developing best practices for maintenance of gill health of farmed salmon. • On average, 38% of the resected filament length had regrown in 20 weeks. • Filaments with higher level of resection showed a higher degree of regeneration. • The degree of regeneration showed significant inter- and intra-individual variation. • Neither fish size nor growth rate influenced gill tissue regeneration. • Regenerated tissue consisted of differentiated cells that appeared functional. [ABSTRACT FROM AUTHOR]

The principles of the human spinal cord development constitute the basis for understanding of appearance of congenital abnormalities of the CNS development, which make 7 % of the total number of malformations in the embryonic period of human’s development. Purpose – to find out the cytoarchitectonic structure of the spinal cord segments of human fetuses with anencephaly, their morphometric parameters and the degree of the proliferation of neural stem cells. Materials and methods – anatomical and histological, immunohistochemical and morphometric research was carried out related to the spinal cord of 4 human fetuses with anencephaly of the gestational period of 17–18 weeks. Results. The length of the spinal cord of 17–18 weeks anencephalic fetuses corresponds to the length of human fetuses without malformations of 11–12 weeks, the rest macrometric parameters – 8–9 weeks. The largest area of grey matter was that of segments at the level of lumbosacral and cervical enlargements, the least one at the level of thoracic segments. The specific gravity of neuroepithelium in the grey matter of cervical, thoracic, lumbar and sacral segments was 0.4, 0.1, 0.6, 1.6 % respectively. The expression of the proliferation protein in the spinal cord neuroepithelium segments of anencephalic fetuses is approaching 0 %. However, in the ventral horns near the location of neural complexes single mitoses of glial cells occur. In quantitative terms, in the ventral horns 1.5 % of glial cells reacted, while in the dorsal ones – 0.6 %. The expression of vimentin in the mantle and marginal layers is poor. On the border between the ventral and dorsal horns an insignificant number of fibers have a radial direction. Moderate expression of synaptophysin was observed in the marginal layer, except for cuneate fasciculi where the relatively weak expression has been established, which testifies to the insufficient myelination of the conduction tracts fibers. Conclusions. Macro- and morphometric parameters of the spinal cord of human fetuses with 17–18 week anencephaly point out to the significant retardation in development. Numerous disorders in the structural organization of both grey matter and white matter have been found out. The proliferation of neural stem cells in neuroepithelium is approaching 0 %.

Although human induced pluripotent stem cells (hiPSCs) hold great potential for the study of human diseases affecting disparate cell types, they have been underutilized in seeking mechanistic insights into the pathogenesis of congenital craniofacial disorders. Craniofrontonasal syndrome (CFNS) is a rare X-linked disorder caused by mutations in EFNB1 and characterized by craniofacial, skeletal, and neurological anomalies. Heterozygous females are more severely affected than hemizygous males, a phenomenon termed cellular interference that involves mosaicism for EPHRIN-B1 function. Although the mechanistic basis for cellular interference in CFNS has been hypothesized to involve Eph/ephrin-mediated cell segregation, no direct evidence for this has been demonstrated. Here, by generating hiPSCs from CFNS patients, we demonstrate that mosaicism for EPHRIN-B1 expression induced by random X inactivation in heterozygous females results in robust cell segregation in human neuroepithelial cells, thus supplying experimental evidence that Eph/ephrin-mediated cell segregation is relevant to pathogenesis in human CFNS patients.

The development of in vitro models is essential in modern science due to the need for experiments using human material and the reduction in the number of laboratory animals. The complexity of the interactions that occur in living organisms requires improvements in the monolayer cultures. In the work presented here, neuroepithelial stem (NES) cells were differentiated into peripheral-like neurons (PLN) and the phenotype of the cells was confirmed at the genetic and protein levels. Then RNA-seq method was used to investigate how stimulation with pro-inflammatory factors such as LPS and IFNγ affects the expression of genes involved in the immune response in human fibroblast-like synoviocytes (HFLS). HFLS were then cultured on semi-permeable membrane inserts, and after 24 hours of pro-inflammatory stimulation, the levels of cytokines secretion into the medium were checked. Inserts with stimulated HFLS were introduced into the PLN culture, and by measuring secreted ATP, an increase in cell activity was found in the system. The method used mimics the condition that occurs in the joint during inflammation, as observed in the development of diseases such as rheumatoid arthritis (RA) or osteoarthritis (OA). In addition, the system used can be easily modified to simulate the interaction of peripheral neurons with other cell types.

The aim of this study was to examine the influence of acrylamide (ACR), a common neurotoxin, on the neuroepithelial cells utilizing in ovo model for embryonic brain development. On day five (E5), 75 eggs with living embryos were randomly divided into three groups: one control and two experimental (n=25) and injected with 0.7% NaCl and/or ACR saline solution at the dose of 30 µg or 300 µg per egg, respectively. The injections were performed directly into the amniotic fluid, and after 7 h of incubation, tissues the brain was collected Additionally, for the brain microstructure evaluation brain tissues were obtained from 10th day embryos. Immunohistochemical localization of caspase-3 and histochemical staining demonstrated deterioration and significant damage to neuroepithelial cells and affected caspase-3 distribution/expression in brain. Results of biochemical assays showed increased activity of enzymes (SOD, AChE, BuChE) whereas ACR had no impact on the MDA concentration. This suggests that ACR has no direct impact on the caspases, and its action is an effect of SOD response to free radicals probably. ACR has an impact on the activity of cholinergic nerves and brain cytoarchitecture of the developing embryos. All of the observed effects suggests serious influence of ACR on the developing brain by several different mechanisms. [ABSTRACT FROM AUTHOR]

Available studies that have examined O2 sensing in fish have indicated that oxygen‐sensitive neuroepithelial cells (NECs) are O2 sensors in the gills and initiate cardiorespiratory reflexes in aquatic vertebrates. This is the first study describing the occurrence of NECs in accessory respiratory organs in the air‐breathing catfish Clarias gariepinus. Immunocytochemical stainings with specific neuronal markers such as nNOS, VAchT, 5‐HT and TH have been shown to be very useful for location and distribution of these cells in the gill fans and suprabranchial chamber that take origin from the transformation of the gill tissue. But the response of these putative O2 chemoreceptors, their role in the respiratory reflexes and their innervation await investigation. [ABSTRACT FROM AUTHOR]

The review addresses the features of the establishment of respiratory activity in the ancient taxa, cyclostomes and fish, which allowed them to adapt to aquatic habitats with a low oxygen level. The brainstem of cyclostomes and fish contains a basic set of nuclei that provides the formation of adequate respiratory activity. The latter is mediated by the universal excitatory and inhibitory neurotransmitters (glutamate, GABA, glycine), suggesting the existence of pivotal, evolutionarily conserved mechanisms to reproduce respiratory oscillations. The qualities of water as a habitat with a reduced oxygen tension determine a high significance of branchial and extrabranchial oxygen-sensitive chemoreceptors which share similar features with highly specialized mammalian oxygen receptors. Neurophysiological details of the respiratory rhythm generator machinery as well as peculiarities of respiratory adaptation to fluctuations in water oxygen tension (PwO2) in agnathans (cyclostomes) and gnathostome fish support the concept of a close relationship between the evolutionarily "verified" adaptive mechanisms regardless of the level of organization of individual vertebrate classes. [ABSTRACT FROM AUTHOR]

The fly photoreceptor has long been used as a model to study sensory neuron morphogenesis and retinal degeneration. In particular, elucidating how these cells are built continues to help further our understanding of the mechanisms of polarized cell morphogenesis, intracellular trafficking and the causes of human retinal pathologies. The conserved PAR complex, which in flies consists of Cdc42-PAR6-aPKC-Bazooka, and the transmembrane protein Crumbs (Crb) are key players during photoreceptor morphogenesis. While the PAR complex regulates polarity in many cell types, Crb function in polarity is relatively specific to epithelial cells. Together Cdc42-PAR6-aPKCBazooka and Crb orchestrate the differentiation of the photoreceptor apical membrane (AM) and zonula adherens (ZA), thus allowing these cells to assemble into a neuroepithelial lattice. In addition to its function in epithelial polarity, Crb has also been shown to protect fly photoreceptors from light-induced degeneration, a process linked to Rhodopsin expression and trafficking. Remarkably, mutations in the human Crumbs1 (CRB1) gene lead to retinal degeneration, making the fly photoreceptor a powerful disease model system. [ABSTRACT FROM AUTHOR]

Neuroendocrine cells act as oxygen sensors in animals from fish to humans, but the evolutionary origins of these cells are only just becoming clear.

The evolutionary origins of the hypoxia-sensitive cells that trigger amniote respiratory reflexes – carotid body glomus cells, and ‘pulmonary neuroendocrine cells’ (PNECs) - are obscure. Homology has been proposed between glomus cells, which are neural crest-derived, and the hypoxia-sensitive ‘neuroepithelial cells’ (NECs) of fish gills, whose embryonic origin is unknown. NECs have also been likened to PNECs, which differentiate in situ within lung airway epithelia. Using genetic lineage-tracing and neural crest-deficient mutants in zebrafish, and physical fate-mapping in frog and lamprey, we find that NECs are not neural crest-derived, but endoderm-derived, like PNECs, whose endodermal origin we confirm. We discover neural crest-derived catecholaminergic cells associated with zebrafish pharyngeal arch blood vessels, and propose a new model for amniote hypoxia-sensitive cell evolution: endoderm-derived NECs were retained as PNECs, while the carotid body evolved via the aggregation of neural crest-derived catecholaminergic (chromaffin) cells already associated with blood vessels in anamniote pharyngeal arches.