Human Neural Cells Transiently Express Reelin during Olfactory Placode Development

RESEARCH ARTICLE Human Neural Cells Transiently Express Reelin during Olfactory Placode Development M. Cristina Antal1,2,3,5, Brigitte Samama1,2,3*, M. Said Ghandour4,5, Nelly Boehm1,2,3 1 Institut d'Histologie, Faculté de Médecine, Université de Strasbourg, Strasbourg, France, 2 Fédération de Médecine Translationnelle de Strasbourg, Strasbourg, France, 3 Hôpitaux Universitaires de Strasbourg, Strasbourg, France, 4 Laboratoire d’Imagerie et de Neurosciences Cognitives, CNRS, UMR 7237, Strasbourg, France, 5 CNRS UMR 7357, Strasbourg, France * Abstract OPEN ACCESS Citation: Antal MC, Samama B, Ghandour MS, Boehm N (2015) Human Neural Cells Transiently Express Reelin during Olfactory Placode Development. PLoS ONE 10(8): e0135710. doi:10.1371/journal.pone.0135710 Editor: Hiroaki Matsunami, Duke University, UNITED STATES Received: April 16, 2015 Reelin, an extracellular glycoprotein is essential for migration and correct positioning of neurons during development. Since the olfactory system is known as a source of various migrating neuronal cells, we studied Reelin expression in the two chemosensory olfactory systems, main and accessory, during early developmental stages of human foetuses/ embryos from Carnegie Stage (CS) 15 to gestational week (GW) 14. From CS 15 to CS 18, but not at later stages, a transient expression of Reelin was detected first in the presumptive olfactory and then in the presumptive vomeronasal epithelium. During the same period, Reelin-positive cells detach from the olfactory/vomeronasal epithelium and migrate through the mesenchyme beneath the telencephalon. Dab 1, an adaptor protein of the Reelin pathway, was simultaneously expressed in the migratory mass from CS16 to CS17 and, at later stages, in the presumptive olfactory ensheathing cells. Possible involvements of Reelin and Dab 1 in the peripheral migrating stream are discussed. Accepted: July 26, 2015 Published: August 13, 2015 Copyright: © 2015 Antal et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper. Funding: This study was supported in part by the Conseil Scientifique de la Faculté de Médecine de Strasbourg and by the Programme Hospitalier de Recherche Clinique, Hôpitaux Universitaires de Strasbourg. The funders had no role in study design, data collection and analysis, decision to publish, or preparetion of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Introduction During development of the olfactory system, peripheral neurosensory axons arising from the invaginated placode reach the presumptive olfactory area of the telencephalon, thus mediating olfactory bulb (OB) development. In the main olfactory system, neurosensory cells in the olfactory epithelium (OE), sending axons to the main OB, make synapses with the dendrite of mitral/tufted cells, whereas in the accessory olfactory system, axons arising from the neurosensorial cells of the vomeronasal epithelium (VNE), lying in the vomeronasal organ (VNO), make synapses with mitral/tufted cells in the accessory olfactory bulb. However, in human, the VNO is present during embryonic/foetal development, contains neurosensory-like cells but is no more functional at birth [1]. The olfactory placode (OP), and later the VNO and OE are well known as sources of various migrating neurons toward the telencephalon; among them are GnRH neurons that migrate along the vomeronasal-terminal nerve (VN/TN) [2]. Several guidance molecules have been proposed for guiding olfactory axons and neurons through the mesenchyme toward the PLOS ONE | DOI:10.1371/journal.pone.0135710 August 13, 2015 1 / 14 Olfactory Derived Reelin Neurons in Human Foetuses presumptive OB area and the septal region, respectively. Molecules involved in cell adhesion (anosmin1, laminin, heparane sulphate proteoglycan), transcription factors and neurotransmitters have been described in the literature (review in [3]). Reelin has emerged as an extracellular glycoprotein essential for migration and correct positioning of cortical neurons and for establishment of correct neuronal circuitry during nervous system development; Reelin is expressed during development by different classes of neurons and especially by Cajal-Retzius cells in cortical layer I [4, 5]. During development, Reelin acts mainly through its VLDL and Apo2E receptors, initiating a signalling cascade where an adapter protein Dab 1 is phosphorylated and binds to the intracellular part of the receptor [6–9]. Reelin expression has also been detected in many other regions of the developing central nervous system in addition to cortical layer I, as well as in peripheral organs such as liver, lymphatic endothelial cells, pituitary pars intermedia, adrenal chromaffin cells [10, 11] and in the peripheral part of the olfactory system in mouse embryos [12,13]. Most data about Reelin pathway during development were obtained in rodents and comparisons with human development showed similarities but also some differences [14]. Since, at our knowledge, no data were available about the expression of the Reelin pathway components in the human olfactory system during the period of cell migration, we studied the expression of Reelin and Dab 1 at some stages of the embryonic/early foetal period in human. Here we show that some early neural cells transiently express Reelin at the time they leave the presumptive OE/VNE and that Dab 1 is present in the migratory cell mass and in the presumptive ensheathing cells in the absence of Reelin expression. Materials and Methods Biological samples Twelve human embryos/foetuses ranging from Carnegie stage (CS) 15 to gestational weeks (GW) 12 from legal abortions and one normal brain and nasal medial wall (14 GW) from a foetus without macroscopic malformations addressed to the Pathology Service of the University Hospital for examination following abortion were studied. These embryos/foetuses were collected following requirements and regulations approved by the Medical Ethics Committee of the Faculty of Medicine of Strasbourg. Written informed maternal consents were obtained from an independent physician according to the procedure approved by the ethics committee. 1 CS15, 1 CS16, 1 CS17, 1 CS18, 2 CS 20–21, 3 CS23-24, 2 GW8, 1 GW12 and 1 GW14 embryos/foetuses were used. For the CS18 embryo, only nasal cavities could be studied. Developmental stage of embryos/foetuses was ascertained based on external morphology, peripheral organs and brain development according to O’Rahilly and Müller [15], Wolff-Quenot and Sick [16] and Feess-Higgins and Larroche [17]. Tissues were fixed in Bouin-Holland fixative (13 embryos/foetuses) or buffered formalin (1 foetus) and 5 μm paraffin sections were cut. Microscopic (...truncated)