Downregulation of GluA2 AMPA Receptor Subunits Reduces the Dendritic Arborization of Developing Spinal Motoneurons

Abstract

AMPA receptors lacking the GluA2 subunit allow a significant influx of Ca2+ ions. Although Ca2+-permeable AMPA receptors are a familiar feature at early stages of development, the functional significance of these receptors during the maturation of the nervous system remains to be established. Chicken lumbar motoneurons express Ca2+-permeable AMPA receptors at E6 but the Ca2+ permeability of AMPA receptors decreases ∼3-fold by E11. Considering that activity-dependent changes in intracellular Ca2+ regulates dendritic outgrowth, in this study we investigated whether downregulation of GluA2 expression during a critical period of development alters the dendritic arborization of spinal motoneurons in ovo. We use an avian replication-competent retroviral vector RCASBP (B) carrying the marker red fluorescent protein (RFP) and a GluA2 RNAi construct to downregulate GluA2 expression. Chicken embryos were infected at E2 with one of the following constructs: RCASBP(B)-RFP, RCASBP(B)-RFP-scrambled RNAi, or RCASBP(B)-RFP-GluA2 RNAi. Infection of chicken embryos at E2 resulted in widespread expression of RFP throughout the spinal cord with ≥60% of Islet1/2-positive motoneurons infected, resulting in a significant reduction in GluA2 protein expression. Downregulation of GluA2 expression had no effect on the dendritic arborization of E6 motoneurons. However, downregulation of GluA2 expression caused a significant reduction in the dendritic arborization of E11 motoneurons. Neither motoneuron survival nor maturation of network activity was affected by changes in GluA2 expression. These findings demonstrate that increased GluA2 expression and changes in the Ca2+ permeability of AMPA receptors regulate the dendritic arborization of spinal cord motoneurons during a critical period of development.

Disrupting GluA2-GAPDH Interaction Affects Axon and Dendrite Development

“…has reported that GluA2 subunits are expressed and organized in axonal growth cones of neurons 24 . Overexpressing GluA2 has also been shown to increase dendritic length, arborization and spine density of pyramidal neurons 28 29 30 , while downregulation results in a reduction of dendritic arborization in early spinal motoneurons 34 . A recent study also provided evidence for the localization of GAPDH with GluA2 and L1 at lens fibre cell membranes, further illustrating the potential involvement of this complex in axon formation 35 .…”

Gene expression of NMDA and AMPA receptors in different facial motor neurons

“…On the other hand, some studies suggested that the global transcriptional dysregulation of ionotropic glutamate receptor subunits alone does not account for the selective vulnerability of neurons and may, instead, be involved in the reorganization of the injured spinal cord . This notion may explain why NR2D mRNA in dormant FMNs was not elevated to resist neurodegeneration, as suggested by a study regarding protective pathways .…”

“…Furthermore, of all remodeling activities, synaptic connection elimination and rearrangement around FMNs take place concomitantly to orchestrate dynamic structural changes . One study showed that, in mammalians, the downregulated glutamate receptor expression by short‐interfering RNA against specific regions of the GluR2 transcript significantly reduced the dendritic arborization of motoneurons, but motoneuron survival and network activity were not affected . In another study, the knockdown or overexpression of GluA1 (GluR1) modulated the dendrite elaboration on spinal motor neurons during the developmental phase .…”

“…2,5,10,17 One study showed that, in mammalians, the downregulated glutamate receptor expression by short-interfering RNA against specific regions of the GluR2 transcript significantly reduced the dendritic arborization of motoneurons, but motoneuron survival and network activity were not affected. 28 In another study, the knockdown or overexpression of GluA1 (GluR1) modulated the dendrite elaboration on spinal motor neurons during the developmental phase. 29 This transition is believed to accompany the compensatory change in the functional status of adult motoneurons.…”

The Fine Art of Writing a Message: RNA Metabolism in the Shaping and Remodeling of the Nervous System

“…Besides their function in synaptic transmission, neurotransmitter receptors also have functions in synaptogenesis and neuronal wiring. In chicken, the GluA2 subunit of AMPA receptors is required for the formation of dendritic arborizations (Yoon et al, 2012 ), and in mammalian brains, it can modulate spine formation (Saglietti et al, 2007 ; Lee et al, 2016 ). The murine GABA A receptor can induce synaptogenesis (Oh et al, 2016 ), and it is also required for spine formation (Heinen et al, 2003 ).…”