Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Adult fish exhibit a strong neurogenic capacity due to the persistence of radial glial progenitor cells. In zebrafish, radial glial cells display well-established markers such as the estrogen-synthesizing enzyme (AroB) and the brain lipid binding protein (Blbp), which is known to strongly bind omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA). While Blpb is mainly described in the telencephalon of adult zebrafish, its expression in the remaining regions of the brain is poorly documented. The present study was designed to further investigate Blbp expression in the brain, its co-expression with AroB, and its link with radial glial cells proliferation in zebrafish. We generated a complete and detailed mapping of Blbp expression in the whole brain and show its complete co-expression with AroB, except in some tectal and hypothalamic regions. By performing PCNA and Blbp immunohistochemistry on cyp19a1b-GFP (AroB-GFP) fish, we also demonstrated preferential Blbp expression in proliferative radial glial cells in almost all regions studied. To our knowledge, this is the first complete and detailed mapping of Blbp-expressing cells showing strong association between Blbp and radial glial cell proliferation in the adult brain of fish. Given that zebrafish is now recognized models for studying neurogenesis and brain repair, our data provide detailed characterization of Blbp in the entire brain and open up a broad field of research investigating the role of omega-3 polyunsaturated fatty acids in neural stem cell activity in fish
ISSN: 1567-133X

hal-01237088
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01237088
DOI : 10.1016/j.gep.2015.11.003
PUBMED : 26611722

Éditeur(s) : HAL CCSD
Résumé : Benzophenone derivatives (BPs) are used as UV filters in many different products. These lipophilic compounds were recently described as ubiquitous contaminant of different compartiments of aquatic systems, including fish. In this study, we evaluated estrogenic activity of ten BPs in a model fish species, the zebrafish (Danio rerio), by combining newly developed in vitro and in vivo models. In vitro, three specific zebrafish reporter gene models expressing zebrafish estrogen receptors (ZfERs) in zebrafish hepatic cell line (ZFL) were used.Estrogenic activity of BPs was quantify in vivo by using a newly developed transgenic zebrafish line that expresses green fluorescent protein (GFP) under the control of the cyp19a1b promoter. The cyp19a1b gene codes for the brain aromatase B that is under the control of estrogens. Vitellogenin (Vtg), a marker of estrogenic compound, was used to assess the potential estrogenic effect of certain BPs in male fish. Five of 10 BPs induced an estrogenic activity on the three models: BP2, THB, BP1, 4BP, while BP and 234 BP were non active. We noted diffrence in BPs ranking depending on the zfER subtypes suggesting ?/? receptor selectivity by certain BPs. By quantifying GFP expression in live zebrafish, we confirm the estrogenic activity of some BP, i.e., BP1, THB, 4BP and 44'BP, as shown by their ability to induce GFP in a concentration-dependent manner. However, the ranking of BPs as a function of their estrogenic activity assay is different between models. For instance, 4BP was the most estrogenic compound in vivo but not in vitro. Differences were also noticed regarding the estrogenic activity of BP2. In vitro, BP2 has strong activity but had no effect on GFP in cyp19a1b-GFP embryo. However, BP2 induced strongly Vtg in male. The lack of estrogenic activity of BP2 in embryo may be related to difference of biodisponibility and/or metabolisation of this compound between embryo and adult fish. Our approach allows to characterize the estrogenic potency of emerging pollutants, using innovative in vitro and in vivo assays within a unique model fish species. The differences observed between assays deserve further studies to characterize the behavior of compounds in the different biological models in term of biodisponibility and metabolism.
1. European Conference on the Replacement, Reduction and Refinement of Animal Experiments in Ecotoxicology
Dübendorf, Switzerland

ineris-00971019
https://hal-ineris.archives-ouvertes.fr/ineris-00971019
INERIS : EN-2012-243

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
: In non-mammalian vertebrates, serotonin (5-HT)-producing neurons exist in the paraventricular organ (PVO), a diencephalic structure containing cerebrospinal fluid (CSF)-contacting neurons exhibiting 5-HT or dopamine (DA) immunoreactivity. Because the brain of the adult teleost is known for its neurogenic activity supported, for a large part, by radial glial progenitors, this study addresses the origin of newborn 5-HT neurons in the hypothalamus of adult zebrafish. In this species, the PVO exhibits numerous radial glial cells (RGCs) whose somata are located at a certain distance from the ventricle. To study relationships between RGCs and 5-HT CSF-contacting neurons, we performed 5-HT immunohistochemistry in transgenic tg(cyp19a1b-GFP) zebrafish in which RGCs are labelled with GFP under the control of the cyp19a1b promoter. We show that the somata of the 5-HT neurons are located closer to the ventricle than those of RGCs. RGCs extend towards the ventricle cytoplasmic processes that form a continuous barrier along the ventricular surface. In turn, 5-HT neurons contact the CSF via processes that cross this barrier through small pores. Further experiments using proliferating cell nuclear antigen or 5-bromo-2'-deoxyuridine indicate that RGCs proliferate and give birth to 5-HT neurons migrating centripetally instead of centrifugally as in other brain regions. Furthermore, treatment of adult zebrafish with tryptophan hydroxylase inhibitor causes a significant decrease in the number of proliferating cells in the PVO, but not in the mediobasal hypothalamus. These data point to the PVO as an intriguing region in which 5-HT appears to promote genesis of 5-HT neurons that accumulate along the brain ventricles and contact the CSF.
ISSN: 0953-816X

inserm-00866212
http://www.hal.inserm.fr/inserm-00866212
DOI : 10.1111/ejn.12348
PUBMED : 23981075

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The brain of the adult teleost fish exhibits intense neurogenic activity and an outstanding capability for brain repair. Remarkably, the brain estrogen-synthesizing enzyme, aromatase B, is strongly expressed, particularly in adult fishes, in radial glial cells, which act as progenitors. Using zebrafish, we tested the hypothesis that estrogens affect adult neurogenesis and brain regeneration by modulating the neurogenic activity of radial glial cells. To investigate this, the estrogenic environment was modified through inhibition of aromatase activity, blockade of nuclear estrogen receptors, or estrogenic treatments. Estrogens significantly decreased cell proliferation and migration at the olfactory bulbs/telencephalon junction and in the mediobasal hypothalamus. It also appears that cell survival is reduced at the olfactory bulbs/telencephalon junction. We also developed a model of telencephalic lesion to assess the role of aromatase and estrogens in brain repair. Proliferation increased rapidly immediately after the lesion in the parenchyma of the injured telencephalon, while proliferation at the ventricular surface appeared after 48 h and peaked at 7 days. At this time, most proliferative cells express Sox2, however, none of these Sox2 positive cells correspond to aromatase B-positive radial glial cells. Interestingly, aromatase B expression was significantly reduced 48 h and 7 days after the injury, but surprisingly, at 72 h after lesion, aromatase B expression appeared de novo expressed in parenchyma cells, suggesting a role for this ectopic expression of aromatase in brain repair mechanisms. Altogether these data suggest that estrogens modulate adult, but not reparative neurogenesis, in zebrafish.
ISSN: 0018-506X

inserm-00831715
http://www.hal.inserm.fr/inserm-00831715
DOI : 10.1016/j.yhbeh.2012.04.003
PUBMED : 22521210

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The effects of some progestins on fish reproduction have been recently reported revealing the hazard of this class of steroidal pharmaceuticals. However, their effects at the central nervous system level have been poorly studied until now. Notwithstanding, progesterone, although still widely considered primarily a sex hormone, is an important agent affecting many central nervous system functions. Herein, we investigated the effects of a large set of synthetic ligands of the nuclear progesterone receptor on the glial-specific expression of the zebrafish brain aromatase (cyp19a1b) using zebrafish mechanism-based assays. Progesterone and 24 progestins were first screened on transgenic cyp19a1b-GFP zebrafish embryos. We showed that progesterone, dydrogesterone, drospirenone and all the progesterone-derived progestins had no effect on GFP expression. Conversely, all progestins derived from 19-nortesterone induced GFP in a concentration-dependent manner with EC50 ranging from the low nM range to hundreds nM. The 19-nortestosterone derived progestins levonorgestrel (LNG) and norethindrone (NET) were further tested in a radial glial cell context using U251-MG cells co-transfected with zebrafish ER subtypes (zfER alpha, zfER beta 1 or zfER beta 2) and cyp19a1b promoter linked to luciferase. Progesterone had no effect on luciferase activity while NET and LNG induced luciferase activity that was blocked by ICI 182,780. Zebrafish-ERs competition assays showed that NET and LNG were unable to bind to ERs, suggesting that the effects of these compounds on cyp19a1b require metabolic activation prior to elicit estrogenic activity. Overall, we demonstrate that 19-nortestosterone derived progestins elicit estrogenic activity by inducing cyp19a1b expression in radial glial cells. Given the crucial role of radial glial cells and neuro-estrogens in early development of brain, the consequences of exposure of fish to these compounds require further investigation.
ISSN: 0041-008X

hal-01366373
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01366373
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01366373/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01366373/file/Several%20synthetic%20progestins%20disrupt%20the%20glial%20cell.pdf
DOI : 10.1016/j.taap.2016.05.019

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Estrogens are known as steroid hormones affecting the brain in many different ways and a wealth of data now document effects on neurogenesis. Estrogens are provided by the periphery but can also be locally produced within the brain itself due to local aromatization of circulating androgens. Adult neurogenesis is described in all vertebrate species examined so far, but comparative investigations have brought to light differences between vertebrate groups. In teleost fishes, the neurogenic activity is spectacular and adult stem cells maintain their mitogenic activity in many proliferative areas within the brain. Fish are also quite unique because brain aromatase expression is limited to radial glia cells, the progenitor cells of adult fish brain. The zebrafish has emerged as an interesting vertebrate model to elucidate the cellular and molecular mechanisms of adult neurogenesis, and notably its modulation by steroids. The main objective of this review is to summarize data related to the functional link between estrogens production in the brain and neurogenesis in fish. First, we will demonstrate that the brain of zebrafish is an endogenous source of steroids and is directly targeted by local and/or peripheral steroids. Then, we will present data demonstrating the progenitor nature of radial glial cells in the brain of adult fish. Next, we will emphasize the role of estrogens in constitutive neurogenesis and its potential contribution to the regenerative neurogenesis. Finally, the negative impacts on neurogenesis of synthetic hormones used in contraceptive pills production and released in the aquatic environment will be discussed
ISSN: 0960-0760

hal-01174214
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01174214
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01174214/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01174214/file/Steroid%20modulation%20of%20neurogenesis.pdf
DOI : 10.1016/j.jsbmb.2015.06.011

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, has emerged as an active mediator in many essential functions in the central nervous system of mammals. BDNF plays significant roles in neurogenesis, neuronal maturation and/or synaptic plasticity and is involved in cognitive functions such as learning and memory. Despite the vast literature present in mammals, studies devoted to BDNF in the brain of other animal models are scarse. Zebrafish is a teleost fish widely known for developmental genetic studies and is emerging as model for translational neuroscience research. In addition, its brain shows many sites of adult neurogenesis allowing higher regenerative properties after traumatic injuries. To add further knowledge on neurotrophic factors in vertebrate brain models, we decided to determine the distribution of bdnf mRNAs in the larval and adult zebrafish brain and to characterize the phenotype of cells expressing bdnf mRNAs by means of double staining studies. Our results showed that bdnf mRNAs were widely expressed in the brain of 7 days old larvae and throughout the whole brain of mature female and male zebrafish. In adults, bdnf mRNAs were mainly observed in the dorsal telencephalon, preoptic area, dorsal thalamus, posterior tuberculum, hypothalamus, synencephalon, optic tectum and medulla oblongata. By combining immunohistochemistry with in situ hybridization, we showed that bdnf mRNAs were never expressed by radial glial cells or proliferating cells. By contrast, bdnf transcripts were expressed in cells with neuronal phenotype in all brain regions investigated. Our results provide the first demonstration that the brain of zebrafish expresses bdnf mRNAs in neurons and open new fields of research on the role of the BDNF factor in brain mechanisms in normal and brain repairs situations.
ISSN: 1932-6203

hal-01359562
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01359562
DOI : 10.1371/journal.pone.0158057
PUBMED : 27336917

Éditeur(s) : HAL CCSD
Résumé : International audience
Estrogens affect brain development of vertebrates, not only by impacting activity and morphology of existing circuits, but also by modulating embryonic and adult neurogenesis. The issue is complex as estrogens can not only originate from peripheral tissues, but also be locally produced within the brain itself due to local aromatization of androgens. In this respect, teleost fishes are quite unique because aromatase is expressed exclusively in radial glial cells, which represent pluripotent cells in the brain of all vertebrates. Expression of aromatase in the brain of fish is also strongly stimulated by estrogens and some androgens. This creates a very intriguing positive auto-regulatory loop leading to dramatic aromatase expression in sexually mature fish with elevated levels of circulating steroids. Looking at the effects of estrogens or anti-estrogens in the brain of adult zebrafish showed that estrogens inhibit rather than stimulate cell proliferation and newborn cell migration. The functional meaning of these observations is still unclear, but these data suggest that the brain of fish is experiencing constant remodeling under the influence of circulating steroids and brain-derived neurosteroids, possibly permitting a diversification of sexual strategies, notably hermaphroditism. Recent data in frogs indicate that aromatase expression is limited to neurons and do not concern radial glial cells. Thus, until now, there is no other example of vertebrates in which radial progenitors express aromatase. This raises the question of when and why these new features were gained and what are their adaptive benefits. This article is part of a Special Issue entitled: Nuclear receptors in animal development.
Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms

Droits : info:eu-repo/semantics/OpenAccess
hal-01102449
https://hal.archives-ouvertes.fr/hal-01102449
https://hal.archives-ouvertes.fr/hal-01102449/document
https://hal.archives-ouvertes.fr/hal-01102449/file/Coumailleau%20et%20al%20final%20manuscript.pdf
DOI : 10.1016/j.bbagrm.2014.07.002

Éditeur(s) : HAL CCSD
Résumé : International audience
The epigenetic mark 5-hydroxymethylcytosine (5hmC) is a cytosine modification that is abundant in the central nervous system of mammals and which results from 5-methylcytosine oxidation by TET enzymes. Such a mark is suggested to play key roles in the regulation of chromatin structure and gene expression. However, its precise functions still remain poorly understood and information about its distribution in non-mammalian species is still lacking. Here, the distribution of 5hmC was investigated in the brain of adult zebrafish, African claw frog, and mouse in a comparative manner. We show that zebrafish neurons are endowed with high levels of 5hmC, whereas quiescent or proliferative neural progenitors show low to undetectable levels of the modified cytosine. In the brain of larval and juvenile Xenopus, 5hmC is also detected in neurons, while ventricular proliferative cells do not display this epigenetic mark. Similarly, 5hmC is enriched in neurons compared to neural progenitors of the ventricular zone in the mouse developing cortex. Interestingly, 5hmC colocalized with the methylated DNA binding protein MeCP2 and with the active chromatin histone modification H3K4me2 in mouse neurons. Taken together, our results show an evolutionarily conserved cerebral distribution of 5hmC between fish and tetrapods and reinforce the idea that 5hmC fulfills major functions in the control of chromatin activity in vertebrate neurons. J. Comp. Neurol. 525:478-497, 2017. © 2016 Wiley Periodicals, Inc.
Journal of Comparative Neurology

hal-01439354
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01439354
DOI : 10.1002/cne.24077
PUBMED : 27414756