Abstract
BackgroundA number of studies have separately shown that the neuregulin1 (NRG1)/ErbB4 system and NMDA-type glutamate receptors (NMDARs) are involved in several aspects of neuronal migration. In addition, intracellular calcium fluctuations play central roles in neuronal motility. Stable expression of the tyrosine kinase receptor ErbB4 promotes migratory activity in the neural progenitor cell line ST14A upon NRG1 stimulation. In this work we analyzed the potential interactions between the NRG1/ErbB4 system and NMDARs in the ST14A migratory process as well as its calcium dependence.ResultsRT-PCR studies have shown that both native ST14A cells (non-expressing ErbB4), as well as ErbB4-transfected cells express low levels of a restricted number of NMDAR subunits: NR1, NR2C, NR2D and NR3B. The resulting NMDAR would form Ca2+ channels characterized by low Mg2+-sensitivity and low Ca2+-permeability, generating small, long-lasting currents. Ca2+-imaging experiments showed slow [Ca2+]i increases in 45% of the cells following 8 μM NMDA stimulation. Basal migration of ErbB4-transfected ST14A cells was unaffected by 18 hrs NMDA incubation. However, over the same incubation time, NMDA was able to significantly enhance NRG1-induced migration. Pre-incubation with the intracellular calcium chelator BAPTA-AM reduced both NRG1- and NRG1/NMDA-stimulated migration, suggesting the involvement of Ca2+ in these processes. NRG1 stimulation of ErbB4-transfected ST14A cells induced a sustained, long-lasting increase in [Ca2+]i, in 99% of the cells. These intracellular Ca2+ signals could be ascribed to both release from intracellular stores and influx from the extracellular medium trough a mechanism of store-operated calcium entry (SOCE). Short-time co-incubation of NMDA and NRG1 did not substantially modify the NRG1-induced intracellular calcium signals.ConclusionsIn summary, NRG1 stimulation of the ErbB4 receptor exerts a sustained [Ca2+]i increase in ST14A neural progenitors; NRG1-induced migration is Ca2+-dependent and can be positively modulated by activation of the NMDA receptor.
Highlights
A number of studies have separately shown that the neuregulin1 (NRG1)/ErbB4 system and NMDAtype glutamate receptors (NMDARs) are involved in several aspects of neuronal migration
In vivo studies demonstrate that the NRG1/ErbB4 system is involved in tangential migration of olfactory bulb (OB) interneuron precursors in the rostral migratory stream (RMS) [7] and of cortical interneuron precursors migrating from the ventral telencephalon [8]
We tested the expression of all known NMDAR subunits in wt ST14A cells by Reverse Transcription (RT)-PCR. wt ST14A cells were grown at 33°C for 18 hrs in 2% FBS Dulbecco’s modified Eagle’s medium (DMEM) and were harvested for RNA extraction
Summary
A number of studies have separately shown that the neuregulin (NRG1)/ErbB4 system and NMDAtype glutamate receptors (NMDARs) are involved in several aspects of neuronal migration. Stable expression of the tyrosine kinase receptor ErbB4 promotes migratory activity in the neural progenitor cell line ST14A upon NRG1 stimulation. In this work we analyzed the potential interactions between the NRG1/ErbB4 system and NMDARs in the ST14A migratory process as well as its calcium dependence. Receptor-ligand interaction induces the homo- or heterodimerization with other members of the ErbB receptor family, which in turn results in the activation of several intracellular signalling pathways and the induction of cellular responses including migration of neuronal precursor cells [4,5,6]. NMDARs appear to be involved in several modes of migration in vivo, such as radial migration of cerebellar granule cells and tangential/radial migration in the developing cortex [10,11,12,13,14]
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