Ionotropic glutamate receptors (iGluRs) do not only mediate the majority of excitatory neurotransmission in the vertebrate CNS, but also modulate pre- and postnatal neurogenesis. Most of the studies on the developmental role of iGluRs are performed on neural progenitors and neural stem cells (NSCs). We took a step back in our study by examining the role of iGluRs in the earliest possible cell type, embryonic stem cells (ESCs), by looking at the mRNA expression of the major iGluR subfamilies in undifferentiated mouse ESCs. For that, we used two distinct murine ES cell lines, 46C ESCs and J1 ESCs. Regarding 46C ESCs, we found transcripts of kainate receptors (KARs) (GluK2 to GluK5), AMPA receptors (AMPARs) (GluA1, GluA3, and GluA4), and NMDA receptors (NMDARs) (GluN1, and GluN2A to GluN2D). Analysis of 46C-derived cells of later developmental stages, namely neuroepithelial precursor cells (NEPs) and NSCs, revealed that the mRNA expression of KARs is significantly upregulated in NEPs and, subsequently, downregulated in NSCs. However, we could not detect any protein expression of any of the KAR subunits present on the mRNA level either in ESCs, NEPs, or NSCs. Regarding AMPARs and NMDARs, GluN2A is weakly expressed at the protein level only in NSCs. Matching our findings for iGluRs, all three cell types were found to weakly express pre- and postsynaptic markers of glutamatergic synapses only at the mRNA level. Finally, we performed patch-clamp recordings of 46C ESCs and could not detect any current upon iGluR agonist application. Similar to 46C ESCs, J1 ESCs express KARs (GluK2 to GluK5), AMPARs (GluA3), and NMDARs (GluN1, and GluN2A to GluN2D) at the mRNA level, but these transcripts are not translated into receptor proteins either. Thus, we conclude that ESCs do not contain functional iGluRs, although they do express an almost complete set of iGluR subunit mRNAs.
Keywords: ESCs, neuroepithelial cells, neural stem cells, synaptic markers, qRT-PCR, patch-clamp recordings
Citation: Pachernegg S, Joshi I, Muth-Köhne E, Pahl S, Münster Y, Terhag J, Karus M, Werner M, Ma-Högemeier Z-L, Körber C, Grunwald T, Faissner A, Wiese S and Hollmann M (2013) Undifferentiated embryonic stem cells express ionotropic glutamate receptor mRNAs. Front. Cell. Neurosci. 7:241. doi: 10.3389/fncel.2013.00241
Received: 28 July 2013; Accepted: 13 November 2013;
Published online: 03 December 2013.
Edited by:Dieter Wicher, Max Planck Institute for Chemical Ecology, Germany
Reviewed by:Josef Bischofberger, University of Basel, Switzerland
Copyright © 2013 Pachernegg, Joshi, Muth-Köhne, Pahl, Münster, Terhag, Karus, Werner, Ma-Högemeier, Körber, Grunwald, Faissner, Wiese and Hollmann. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Michael Hollmann, Department of Biochemistry I - Receptor Biochemistry, Ruhr University Bochum, Building NC, Level 6, Room 170, Universitaetsstr. 150, D-44780 Bochum, Germany e-mail: email@example.com
†Present address: Elke Muth-Köhne, Fraunhofer Institute for Molecular Biology and Applied Ecology, Aachen, Germany; Michael Karus, Institute of Reconstructive Neurobiology, University of Bonn, Bonn, Germany;
Markus Werner, Department of Cell Physiology, Ruhr University Bochum, Bochum, Germany;
Christoph Körber, Institute of Anatomy and Cell Biology, Heidelberg University, Heidelberg, Germany;
Thomas Grunwald, Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany
‡These authors have contributed equally to this work.