Neuregulin 1 expression and electrophysiological abnormalities in the Neuregulin 1 transmembrane domain heterozygous mutant mouse.

Leonora E Long,Cynthia Shannon Weickert,Xu-Feng Huang,Paul Anderson,Didier Pinault,Alex Shaw,Nigel C Jones,Terence J O’Brien,Shijie Liu,Elisabeth Frank,Tim Karl,Takanori Hashimoto

doi:10.1371/journal.pone.0124114

Abstract

BackgroundThe Neuregulin 1 transmembrane domain heterozygous mutant (Nrg1 TM HET) mouse is used to investigate the role of Nrg1 in brain function and schizophrenia-like behavioural phenotypes. However, the molecular alterations in brain Nrg1 expression that underpin the behavioural observations have been assumed, but not directly determined. Here we comprehensively characterise mRNA Nrg1 transcripts throughout development of the Nrg1 TM HET mouse. In addition, we investigate the regulation of high-frequency (gamma) electrophysiological oscillations in this mutant mouse to associate molecular changes in Nrg1 with a schizophrenia-relevant neurophysiological profile.MethodsUsing exonic probes spanning the cysteine-rich, epidermal growth factor (EGF)-like, transmembrane and intracellular domain encoding regions of Nrg1, mRNA levels were measured using qPCR in hippocampus and frontal cortex from male and female Nrg1 TM HET and wild type-like (WT) mice throughout development. We also performed electrophysiological recordings in adult mice and analysed gamma oscillatory at baseline, in responses to auditory stimuli and to ketamine.ResultsIn both hippocampus and cortex, Nrg1 TM HET mice show significantly reduced expression of the exon encoding the transmembrane domain of Nrg1 compared with WT, but unaltered mRNA expression encoding the extracellular bioactive EGF-like and the cysteine-rich (type III) domains, and development-specific and region-specific reductions in the mRNA encoding the intracellular domain. Hippocampal Nrg1 protein expression was not altered, but NMDA receptor NR2B subunit phosphorylation was lower in Nrg1 TM HET mice. We identified elevated ongoing and reduced sensory-evoked gamma power in Nrg1 TM HET mice.InterpretationWe found no evidence to support the claim that the Nrg1 TM HET mouse represents a simple haploinsufficient model. Further research is required to explore the possibility that mutation results in a gain of Nrg1 function.

Highlights

Genome-wide association studies have identified neuregulin 1 (NRG1) as a candidate risk gene for schizophrenia [1,2,3,4,5]
Schizophrenia is characterised by increased expression of NRG1 splice variants and altered isoform expression ratios, which are linked to polymorphisms in intronic and promoter regions of the gene [6,7,8,9], possibly via high nucleotide diversity in the regulatory regions of NRG1 leading to increased molecular change [9]
Nrg1 transmembrane domain mRNA is reduced in Nrg1 TM HET mice but the mRNA encoding the bioactive epidermal growth factor (EGF)-like domain is not reduced

Summary

Introduction

Genome-wide association studies have identified neuregulin 1 (NRG1) as a candidate risk gene for schizophrenia [1,2,3,4,5]. An understanding of how Nrg expression and neurobiological function are changed in Nrg TM HET mice is critical to determine which aspects of the Nrg1-related molecular and cellular changes found in schizophrenia may be recapitulated in this mouse, and to better model the relationships between Nrg alterations and pathophysiological/ behavioural outcomes. The Neuregulin 1 transmembrane domain heterozygous mutant (Nrg TM HET) mouse is used to investigate the role of Nrg in brain function and schizophrenia-like behavioural phenotypes. We investigate the regulation of high-frequency (gamma) electrophysiological oscillations in this mutant mouse to associate molecular changes in Nrg with a schizophrenia-relevant neurophysiological profile

Methods

Results

Conclusion