Nucleolar binding of an anti‐NMDA receptor antibody in hydra: a non‐canonical role for an NMDA receptor protein?

Abstract

Two emerging concepts in cell biology are the back-and-forth trafficking of receptor proteins and nuclear transcription factors between the nucleus and the cell membrane, and the alternative splicing of messenger RNA to produce similar proteins targeted to different cell sites. Recent evidence suggests that the nucleolus is a dynamic structure whose components may be involved in both types of trafficking. In the nervous system of higher animals, the N-methyl-D-aspartate (NMDA)-specific glutamate receptor has various roles in development and cell communication. It is involved in learning, memory, axonal guidance and nerve regeneration. We have reported earlier that the NR1 subunit of the NMDA receptor is present in the cell periphery and the nucleus of stem cells, neurons and epitheliomuscular cells of the early-evolved cnidarian, Hydra vulgaris (Scappaticci et al., 2004. Cell Tissue Res 316:263-270); it is involved in coordinating hydra's neuroeffector systems (Kass-Simon and Scappaticci, 2003. Hydrobiologia 530/531:67-71; Pierobon et al., 2004. Eur J Neurosci 20:2598-2604; Scappaticci and Kass-Simon, 2008. Comp Biochem Physiol A 150:415-422; Kay and Kass-Simon, 2009. Bio Bull 216:113-129). Here we report immunocytochemical experiments, using a mouse monoclonal antibody raised against the mammalian NR1 receptor subunit, and an in silico genomic and gene expression analysis identifying the homologues in hydra of mammalian NR1 and fibrillarin (FBL) genes, and their expressed proteins. The experiments reveal that the NR1 antibody specifically labels the nucleoli of large and small interstitial cells (stem cells), nematoblasts, neuroblasts, and epitheliomusclar cells; antibody labeling of the nucleolar marker, FBL, confirms the nucleolar localization of NR1 antibody labeling. Genomic analysis reveals that NR1 and FBL genes are conserved in hydra, and suggests that there are at least two NR1 splice variants, one of which contains both nuclear and nucleolar targeting signals. The finding that an NR1 receptor subunit (or a portion of it) appears in nucleoli of hydra cells is unique, and has not been reported for any other organism. Its presence in nucleoli of hydra may signal the existence of a yet-undescribed shuttle mechanism between the cell surface and the nucleous, or the alternative deployment of NR1 splice variants to different cell sites.

Nuclear Localization and Functional Characteristics of Voltage-gated Potassium Channel Kv1.3

“…The results show that nuclear Kv1.3 channel binds to the UBF1 transcription factor, which participates in RNA polymerase I activity, mediating ribosomal RNA synthesis. It was reported that the NR1 subunit of the N-methyl-D-aspartate receptor was found in the nucleoli of hydra cells, which could serve as a regulator for ribosomal subunit production (47). Therefore, nuclear Kv1.3 channels appear to play the role of regulators in ribosome biogenesis, although this possibility needs to be studied further.…”

Pluripotential GluN1 (NMDA NR1): Functional Significance in Cellular Nuclei in Pain/Nociception

“…1. The putative NLS and/or nucleolar localization sequences (NoLS) located in cassette 1 of the GluN1 subunit has two short regions rich in basic amino acids, which comprise the NLS and are potentially involved in nucleolar signaling [66,67]. GluN1 subunits are tightly subjected to multiple levels of regulation, affecting subunit expression, subcellular location, and assembly of functional receptors, and their signaling complexes [34].…”

“…DNA methylation, p53 activation, and post-transcriptional histone deacetylase are processes in the chromatin [86]. The GluN subunit has roles in cellular development and communication, reflecting dynamic cell retraction [34,67]. Early-life stress is a potent risk factor for the development of chronic pain, although the underlying mechanisms remain poorly understood.…”

Microwave-Induced Structural and Functional Injury of Hippocampal and PC12 Cells Is Accompanied by Abnormal Changes in the NMDAR-PSD95-CaMKII Pathway

“…NO enters the presynaptic membrane, which causes the phosphorylation of protein, the influx of Ca 2+ and the glycosylation of protein kinase C. It then activates the expression of some early immediate genes (c-fos and c-jun) and transcription factors (CREB). The transcription factors change the expression of nuclear genes, including the subunit gene of NMDARs, and ultimately cause the synthesis of different proteins [30][31][32] .…”