Steroid modulation of neurogenesis: Focus on radial glial cells in zebrafish Pellegrini Elisabeth a, *, Diotel Nicolas a,b,c , Vaillant-Capitaine Colette a , Pérez Maria Rita a,d , Gueguen Marie-Madeleine a , Nasri Ahmed a,e , Cano Nicolau Joel a , Kah Olivier a a Inserm U1085, Université de Rennes 1, Research Institute in Health, Environment and Occupation, 35000 Rennes, France b Inserm UMR 1188, Diabète athérothrombose Thérapies Réunion Océan Indien (DéTROI), plateforme CYROI, Sainte-Clotilde F-97490, France c Université de La Réunion, UMR 1188, Sainte-Clotilde F-97490, France d Laboratorio de Ictiología, Instituto Nacional de Limnología (INALI. CONICET-UNL), Paraje El Pozo, Ciudad Universitaria UNL, 3000 Santa Fe, Argentina e Laboratoire de Biosurveillance de l’Environnement, Unité d’Ecologie côtière et d’Ecotoxicologie, Faculté des Sciences de Bizerte, Zarzouna 7021, Tunisia A R T I C L E I N F O Article history: Received 30 March 2015 Received in revised form 1 June 2015 Accepted 16 June 2015 Available online xxx Keywords: Zebrafish Radial glial progenitor cells Neurosteroids Aromatase Estradiol Endocrine disruptors A B S T R A C T 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. ã 2015 Elsevier Ltd. All rights reserved. 1. Introduction Despite the early establishment of the basic architecture of neural circuits, the adult brains of all vertebrates studied so far retain the capacity of remodeling in order to adapt their neuronal networks to environmental demands or to damages [1,2]. For the past twenty years, the dogma according to which the number of neurons is defined at birth without new formation and replacement in adulthood has been challenged by a series of research highlighting the capacity of the adult brain to generate new cells. The pioneering work of Altman and Das in 1960s reported the production of new neurons in a very limited number of brain areas in rodents [3]. This new concept of adult neurogenesis, initially rejected, was reinforced two decades later by the work of Nottebohm who has demonstrated that neurons were generated in the forebrain of adult birds and incorporated in the vocal control center, allowing the annual learning of new song [4] . Since the 1990s, with the introduction of new methods for labeling dividing cells, the existence of proliferative activity in the adult brain of mammals was indeed evidenced in confined regions such as the subventricular zone of the lateral ventricles and the dentate gyrus of the hippocampus [5–7] and findings strongly suggest that adult neurogenesis also takes place in the hypothalamus [8–10]. With the development of the thymidine analog 5-bromo2 0 -deoxyuridine (BrdU) incorporation technique as a tool to label newborn neurons, it clearly appeared that adult neurogenesis is not limited to mammals and birds but is a feature * Corresponding author at: Research Institute in Health, Environment and Occupation, INSERM U1085, SFR Biosit, Université de Rennes 1, Campus de Beaulieu, 35 042 Rennes cedex, France. Fax: +33 2 23 23 67 94. E-mail address: elisabeth.pellegrini@univ-rennes1.fr (P. Elisabeth). http://dx.doi.org/10.1016/j.jsbmb.2015.06.011 0960-0760/ ã 2015 Elsevier Ltd. All rights reserved. Journal of Steroid Biochemistry & Molecular Biology xxx (2015) xxx–xxx G Model SBMB 4435 No. of Pages 10 Please cite this article in press as: P. Elisabeth, et al., Steroid modulation of neurogenesis: Focus on radial glial cells in zebrafish, J. Steroid Biochem. Mol. Biol. (2015), http://dx.doi.org/10.1016/j.jsbmb.2015.06.011 Contents lists available at ScienceDirect Journal of Steroid Biochemistry & Molecular Biology journal homepage: www.else vie r.com/locate /jsbmb