Tenascin-C mRNA is expressed in cranial neural crest cells,in some placodal derivatives,and in discrete domains of the embryonic zebrafish brain

A partial zebrafish tenascin-C cDNA clone was isolated from an embryonic zebrafish cDNA library on the basis of homology to mouse tenascin-C. The expression pattern in the head of embryonic zebrafish was analyzed by in situ hybridization. Tenascin-C mRNA was detected in neural crest cells during the period of their migration and differentiation. Expression also occurred in differentiating placodal tissues and in mesodermal cells. In the developing brain, tenascin-C mRNA was expressed in specific domains. In the hindbrain the pattern of the domains was dynamic. At 18 to 22 h postfertilization, expression was widespread in rhombomeres 3, 5, and 6, confined to periventricular cells in rhombomere 2, and not detectable in rhombomere 4. At 32 h postfertilization, tenascin-C was expressed at the rhombomere boundaries. In contrast to the hindbrain, the pattern in the forebrain and midbrain did not show any major changes between 22 and 32 h postfertilization. Domains expressing tenascin-C alternated with regions devoid of it. The most anterior domain of expression was observed at the telencephalic-diencephalic border, surrounding the optic recess. A second domain, at the border between the diencephalon and the midbrain, and a third domain, in the caudal midbrain tegmentum, appeared restricted to the basal plate. Additionally, expression of tenascin-C mRNA was detected in the hypothalamus and in the developing epiphysis. These expression patterns suggest that tenascin-C may play a role in neural crest cell migration and during the differentiation of neural crest, placodal, and mesodermal derivatives. In the developing brain, tenascin-C may be involved in the consolidation of different regional identities. © 1995 John Wiley & Sons, Inc.     

Integrating behavioral and neural data in a model of zebrafish network interaction

The spinal neural networks of larval zebrafish (Danio rerio) generate a variety of movements such as escape, struggling, and swimming. Various mechanisms at the neural and network levels have been proposed to account for switches between these behaviors. However, there are currently no detailed demonstrations of such mechanisms. This makes determining which mechanisms are plausible extremely difficult. In this paper, we propose a detailed biologically plausible model of the interactions between the swimming and escape networks in the larval zebrafish, while taking into account anatomical and physiological evidence. We show that the results of our neural model generate the expected behavior when used to control a hydrodynamic model of carangiform locomotion. As a result, the model presented here is a clear demonstration of a plausible mechanism by which these distinct behaviors can be controlled. Interestingly, the networks are anatomically overlapping, despite clear differences in behavioral function and physiology.     

Nonylphenol induces the death of neural stem cells due to activation of the caspase cascade and regulation of the cell cycle

Endocrine disruptors (EDs) are a great concern throughout the world, because they have adverse effects on human health and wildlife. In the present study, we investigated the effects of EDs on the proliferation and survival of murine neural stem cells (NSCs). In contrast to bisphenol A, phthalic acid benzyl n-butyl ester, phthalic acid di-n-butyl ester and phthalic acid di(2-ethylhexyl) ester, the treatment of NSCs with 4-nonylphenol for 24 h inhibited cell growth in a concentration-dependent manner. In addition, treatment with 4-nonylphenol resulted in nuclear condensation and DNA fragmentation (morphological changes due to apoptosis) in NSCs after 12 h of exposure, and activated caspase-3 after 6 h and 9 h of exposure. Furthermore, an exposure to 4-nonylphenol led to the accumulation of cells at the G2/M phase interface and down-regulated the protein levels of cyclin A and B1, which are the major regulatory proteins at the G2 to M transition of the cell cycle. Together, these results indicate that, in contrast to other EDs, 4-nonylphenol may exhibit a potent cytotoxicity through apoptosis via the caspase cascade and cell cycle arrest at the G2/M phase, and suggest that 4-nonylphenol may affect neurogenesis in the CNS.     

Circletail, a new mouse mutant with severe neural tube defects: chromosomal localization and interaction with the loop-tail mutation.

Circletail (Crc) is a new mouse mutant that exhibits a severe form of neural tube defect, craniorachischisis, in which almost the entire neural tube fails to close. This phenotype is seen in very few other mutants, the best characterized of which is loop-tail (Ltap(Lp), referred to hereafter as Lp). We tested the possibility of allelism between Lp and Crc by intercrossing Lp/+ and Crc/+mice. A proportion of double heterozygotes (Lp/+,Crc/+) exhibit craniorachischisis, revealing failure of complementation. However, genetic analysis shows that Crc is not linked to the markers that flank the Lp locus and cannot, therefore, be an allele of Lp. A genome-wide scan has localized the Crc gene to a region of 8.8 cM on central chromosome 15. Partial penetrance of the craniorachischisis phenotype in Crc/+,Lp/+double heterozygotes suggests the existence of a third, unlinked genetic locus that influences the interaction between Crc and Lp.     

The human tissue plasminogen activator-Cre mouse: a new tool for targeting specifically neural crest cells and their derivatives in vivo

The ontogeny of neural crest cells (NCC) involves a number of orchestrated variety of derivatives, including components of the peripheral nervous system and melanocytes. Thus, it represents an excellent model system to investigate mechanisms controlling epithelial-mesenchymal transitions, cell migration and differentiation, as well as cell proliferation and death. We have established a new transgenic line expressing the Cre recombinase under the control of the human tissue plasminogen activator promoter (Ht-PA). The activity of the reporter in the Ht-PA-Cre/R26R embryos is observed as early as Theiler stage 12 in the cephalic mesenchyme. Later, the targeted cells include all the known derivatives of cranial, vagal, and trunk NCC, including craniofacial structures and cranial ganglia, cardiac and endocrine derivatives, melanocytes, peripheral, and enteric nervous system. At the vagal level, the location of presumptive enteric NCC differs from their avian counterparts in their ability to invade the mesenchyme lateral to the neural tube. In contrast to the Wnt1-Cre line, the Ht-PA-Cre line does not target the central nervous system and therefore renders it more specific for NCC. Our Ht-PA-Cre mice represent a novel model to specifically target conditional mutations in migratory NCC.     

Advances of tooth‐derived stem cells in neural diseases treatments and nerve tissue regeneration

Nerous system diseases, both central and peripheral, bring an incredible burden onto patients and enormously reduce their quality of life. Currently, there are still no effective treatments to repair nerve lesions that do not have side effects. Stem cell–based therapies, especially those using dental stem cells, bring new hope to neural diseases. Dental stem cells, derived from the neural crest, have many characteristics that are similar to neural cells, indicating that they can be an ideal source of cells for neural regeneration and repair. This review summarizes the neural traits of all the dental cell types, including DPSCs, PDLCs, DFCs, APSCs and their potential applications in nervous system diseases. We have summed up the advantages of dental stem cells in neural repair, such as their neurotrophic and neuroprotective traits, easy harvest and low rejective reaction rate, among others. Taken together, dental stem cells are an ideal cell source for neural tissue regeneration and repair.     

Genomic analysis reveals low tumor mutation burden which may be associated with GNAQ/11 alteration in a series of primary leptomeningeal melanomas

Primary central nervous system melanoma is rare and characterized by a variable prognosis, and no current treatment guidelines exist. We describe the clinical course of a 70‐year‐old female patient diagnosed with primary leptomeningeal melanoma (LMN) whose case represents the diagnostic and management challenges of this tumor. Targeted genomic sequencing of 315 genes from this tumor revealed GNAQ Q209L mutation and low (4 mutations/Megabase) tumor mutation burden (TMB). Wild‐type NRAS, KIT, and BRAF were also observed. A cohort of 4,787 melanomas was subsequently analyzed to identify additional primary central nervous system melanomas, of which 10 additional tumors met pathologic criteria (0.21% of total melanoma cohort). These tumors were genomically assessed according to the same targeted sequencing panel, and 6 of the tumors were also found to harbor a GNAQ mutation. All 10 tumors had low (less than or equal to 2 mutations/Megabase) TMB indicating a potential trend between G‐protein‐coupled receptor (GPCR) alterations and low TMB in LMNs. GPCR alterations were found to significantly correlate with TMB across the cohort of 4,787 melanomas, supporting this potential finding in the limited LMN subset.     

Mast cell-nerve axis with a focus on the human gut

This paper summarizes the current knowledge on the interactions between intestinal mast cells, enteric neurons and visceral afferents which are part of the gut brain axis. The focus of this review is on the relevance of the mast cell-nerve axis in the human intestine. Similarities and important differences in the organization of the mast cell-nerve axis between human and rodents are discussed. Functionally important human mast cell mediators with neural actions in the human ENS are histamine (H1-4 receptors), proteases (PAR1 receptors), several cytokines and chemokines and probably also serotonin (5-HT₃ receptors). On the other hand, mediator release from human intestinal mast cells is modulated by neuropeptides released from enteric and visceral afferent nerves. This article is part of a Special Issue entitled: Mast Cells in Inflammation.     

Melatonin,a calpain inhibitor in the central nervous system: Current status and future perspectives

Dysregulation of neuronal Ca²⁺ and oxidative stress plays an important role in the activation of cysteine proteases including calpains and caspases that contribute to neuronal death. In neurodegenerative diseases, traumatic brain injury, stroke, and neuropathic pain calpain activities are markedly increased. Melatonin is a beneficial supplement in the treatment of central nervous system (CNS) disorders. Melatonin is a potent antioxidant and works as a free-radical scavenger to regulate a large number of molecular pathways, including oxidative stress, inflammation, apoptosis, and cell death under different pathological conditions. However, limited studies have evaluated the inhibitory effect of melatonin on calpains. This review summarizes the current knowledge related to the effects of melatonin on calpains in some of the common CNS disorders.     

Kif11 dependent cell cycle progression in radial glial cells is required for proper neurogenesis in the zebrafish neural tube

Radial glia serve as the resident neural stem cells in the embryonic vertebrate nervous system, and their proliferation must be tightly regulated to generate the correct number of neuronal and glial cell progeny in the neural tube. During a forward genetic screen, we recently identified a zebrafish mutant in the kif11 loci that displayed a significant increase in radial glial cell bodies at the ventricular zone of the spinal cord. Kif11, also known as Eg5, is a kinesin-related, plus-end directed motor protein responsible for stabilizing and separating the bipolar mitotic spindle. We show here that Gfap+ radial glial cells express kif11 in the ventricular zone and floor plate. Loss of Kif11 by mutation or pharmacological inhibition with S-trityl-l-cysteine (STLC) results in monoastral spindle formation in radial glial cells, which is characteristic of mitotic arrest. We show that M-phase radial glia accumulate over time at the ventricular zone in kif11 mutants and STLC treated embryos. Mathematical modeling of the radial glial accumulation in kif11 mutants not only confirmed an ~226× delay in mitotic exit (likely a mitotic arrest), but also predicted two modes of increased cell death. These modeling predictions were supported by an increase in the apoptosis marker, anti-activated Caspase-3, which was also found to be inversely proportional to a decrease in cell proliferation. In addition, treatment with STLC at different stages of neural development uncovered two critical periods that most significantly require Kif11 function for stem cell progression through mitosis. We also show that loss of Kif11 function causes specific reductions in oligodendroglia and secondary interneurons and motorneurons, suggesting these later born populations require proper radial glia division. Despite these alterations to cell cycle dynamics, survival, and neurogenesis, we document unchanged cell densities within the neural tube in kif11 mutants, suggesting that a mechanism of compensatory regulation may exist to maintain overall proportions in the neural tube. We propose a model in which Kif11 normally functions during mitotic spindle formation to facilitate the progression of radial glia through mitosis, which leads to the maturation of progeny into specific secondary neuronal and glial lineages in the developing neural tube.     

Fibroblast growth factor 2 internal ribosome entry site (IRES) activity ex vivo and in transgenic mice reveals a stringent tissue-specific regulation

Fibroblast growth factor 2 (FGF-2) is a powerful mitogen involved in proliferation, differentiation, and survival of various cells including neurons. FGF-2 expression is translationally regulated; in particular, the FGF-2 mRNA contains an internal ribosome entry site (IRES) allowing cap-independent translation. Here, we have analyzed FGF-2 IRES tissue specificity ex vivo and in vivo by using a dual luciferase bicistronic vector. This IRES was active in most transiently transfected human and nonhuman cell types, with a higher activity in p53 -/- osteosarcoma and neuroblastoma cell lines. Transgenic mice were generated using bicistronic transgenes with FGF-2 IRES or encephalomyocarditis virus (EMCV) IRES. Measurements of luciferase activity revealed high FGF-2 IRES activity in 11-d-old embryos (E11) but not in the placenta; activity was high in the heart and brain of E16. FGF-2 IRES activity was low in most organs of the adult, but exceptionally high in the brain. Such spatiotemporal variations were not observed with the EMCV IRES. These data, demonstrating the strong tissue specificity of a mammalian IRES in vivo, suggest a pivotal role of translational IRES- dependent activation of FGF-2 expression during embryogenesis and in adult brain. FGF-2 IRES could constitute, thus, a powerful tool for gene transfer in the central nervous system.     

Elucidation of the role of activin in organogenesis using a multiple organ induction system with amphibian and mouse undifferentiated cells in vitro

Studies performed over the last century have clarified the mechanisms of organ and tissue formation. Mesoderm formation is one of the most important events in early body pattern determination during embryogenesis. In 1988, we found that activin A has mesoderm-inducing activity. As activin A could induce dorsal mesoderm formation, unlike fibroblast growth factor and bone morphogenetic protein, this factor was thought to be the molecular entity of the Spemann-Mangold organizer. Subsequently, the mechanisms of early embryogenesis have been clarified using molecular biological techniques, resulting in the identification of many genes that are involved in organ and tissue development. This finding that activin A could induce dorsal mesoderm formation spurred research into the application of agents that induce organs and tissues in vitro . In this regard, we have shown that many organ types can be induced by activin A in vitro . Moreover, we have found that other types of organs can be induced by changing the conditions of treatment. To date, more than 20 different types of tissues and organs have been successfully induced from Xenopus undifferentiated cells in vitro . In recent years, we have applied these protocols to mouse embryonic stem cells, and we have successfully induced several tissues, such as the pancreas and cardiomyocytes. We are also investigating how the pluripotency of undifferentiated stem cells is regulated. In this review, we summarize the current knowledge regarding activin as a mesoderm-inducing factor and its application for the induction of tissues and organs from undifferentiated cells. Moreover, we provide some examples of in vitro tissue differentiation from mouse embryonic stem cells, which may prove useful in regenerative medicine.     

Accumulation of mutations and somatic selection in aging neural stem/progenitor cells

Genomic instability within somatic stem cells may lead to the accumulation of mutations and contribute to cancer or other age-related phenotypes. However, determining the frequency of mutations that differ among individual stem cells is difficult from whole tissue samples because each event is diluted in the total population of both stem cells and differentiated tissue. Here the ability to expand neural stem/progenitor cells clonally permitted measurement of genomic alterations derived from a single initial cell. C57Bl/6 x DBA/2 hybrid mice were used and PCR analysis with strain-specific primers was performed to detect loss of heterozygosity on nine different chromosomes for each neurosphere. The frequency with which changes occurred in neurospheres derived from 2-month- and 2-year-old mice was compared. In 15 neurospheres derived from young animals both parental chromosomes were present for all nine chromosome pairs. In contrast, 16/17 neurospheres from old animals demonstrated loss of heterozygosity (LOH) on one or more chromosomes and seven exhibited a complete deletion of at least one chromosomal region. For chromosomes 9 and 19 there is a significant bias in the allele that is lost where in each case the C57Bl/6 allele is retained in 6/6 neurospheres exhibiting LOH. These data suggest that aging leads to a substantial mutational load within the neural stem cell compartment which can be expected to affect the normal function of these cells. Furthermore, the retention of specific alleles for chromosomes 9 and 19 suggests that a subset of mutational events lead to an allele-specific survival advantage within the neural stem cell compartment.     

Aging-related changes in astrocytes in the rat retina: imbalance between cell proliferation and cell death reduces astrocyte availability

The aim of this study was to investigate changes in astrocyte density, morphology, proliferation and apoptosis occurring in the central nervous system during physiological aging. Astrocytes in retinal whole-mount preparations from Wistar rats aged 3 (young adult) to 25 months (aged) were investigated qualitatively and quantitatively following immunofluorohistochemistry. Glial fibrillary acidic protein (GFAP), S100 and Pax2 were used to identify astrocytes, and blood vessels were localized using Griffonia simplicifoli a isolectin B4. Cell proliferation was assessed by bromodeoxyuridine incorporation and cell death by TUNEL-labelling and immunolocalization of the apoptosis markers active caspase 3 and endonuclease G. The density and total number of parenchymal astrocytes in the retina increased between 3 and 9 months of age but decreased markedly between 9 and 12 months. Proliferation of astrocytes was detected at 3 months but virtually ceased beyond that age, whereas the proportion of astrocytes that were TUNEL positive and relative expression of active caspase 3 and endonuclease G increased progressively with aging. In addition, in aged retinas astrocytes exhibited gliosis-like morphology and loss of Pax2 reactivity. A small population of Pax2⁺/GFAP⁻ cells was detected in both young adult and aged retinas. The reduction in the availability of astrocytes in aged retinas and other aging-related changes reported here may have a significant impact on the ability of astrocytes to maintain homeostasis and support neuronal function in old age.