Disrupted-in-Schizophrenia (DISC1) Functions Presynaptically at Glutamatergic Synapses

Brady J Maher,Joseph J Loturco,Fabien Tell

doi:10.1371/journal.pone.0034053

Brady J Maher, Joseph J Loturco + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0034053

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Abstract

The pathophysiology of schizophrenia is believed to involve defects in synaptic transmission, and the function of many schizophrenia-associated genes, including DISC1, have been linked to synaptic function at glutamatergic synapses. Here we develop a rodent model via in utero electroporation to assay the presynaptic function of DISC1 at glutamatergic synapses. We used a combination of mosaic transgene expression, RNAi knockdown and optogenetics to restrict both genetic manipulation and synaptic stimulation of glutamatergic neurons presynaptic to other layer 2/3 neocortical pyramidal neurons that were then targeted for whole-cell patch-clamp recording. We show that expression of the DISC1 c-terminal truncation variant that is associated with Schizophrenia alters the frequency of mEPSCs and the kinetics of evoked glutamate release. In addition, we show that expression level of DISC1 is correlated with the probability of glutamate release such that increased DISC1 expression results in paired-pulse depression and RNAi knockdown of DISC1 produces paired-pulse facilitation. Overall, our results support a direct presynaptic function for the schizophrenia-associated gene, DISC1.

Highlights

DISC1 was identified as a schizophrenia susceptibility gene because a chromosomal translocation that results in a c-terminal truncation of the DISC1 gene was found to co-segregate with major mental illness in an extended Scottish pedigree [1,2]
In order to determine whether DISC1 regulates synaptic transmission we used in utero electroporation to alter DISC1 expression in approximately 20% of neocortical layer 2/3 pyramidal neurons by conditionally expressing full-length DISC1, DISC1DC, or constitutive expression of an shRNA previously shown to create effective RNAi knockdown of DISC1 (D1 RNAi [6,14,20]; see methods)
This increase in synaptic activity was present to the same extent in both transfected cells expressing DISC1DC and neighboring non-transfected cells and indicates presynaptic expression of DISC1DC is sufficient to explain the increase in mEPSC frequency

Summary

Introduction

DISC1 was identified as a schizophrenia susceptibility gene because a chromosomal translocation that results in a c-terminal truncation of the DISC1 gene was found to co-segregate with major mental illness in an extended Scottish pedigree [1,2]. Transgenic animals expressing a truncated version of DISC1 (DISC1DC) under control of the CaMKII promoter were shown to display abnormal behavioral phenotypes, enlarged ventricles, decreased levels of cortical dopamine, fewer parvalbumin-positive neurons and altered spine density [10,11]. These studies provide strong evidence for DISC1 having important roles in postsynaptic physiology and structure, evidence exists that suggest DISC1 has important presynaptic functions. Our data provide several lines of evidence that suggest DISC1 has direct functions in presynaptic transmission

Methods

Results

Conclusion