Crybb2 Mutations Consistently Affect Schizophrenia Endophenotypes in Mice

Abstract

As part of the βγ-superfamily, βB2-crystallin (CRYBB2) is an ocular structural protein in the lens, and mutation of the corresponding gene can cause cataracts. CRYBB2 also is expressed in non-lens tissue such as the adult mouse brain and is associated with neuropsychiatric disorders such as schizophrenia. Nevertheless, the robustness of this association as well as how CRYBB2 may contribute to disease-relevant phenotypes is unknown. To add further clarity to this issue, we performed a comprehensive analysis of behavioral and neurohistological alterations in mice with an allelic series of mutations in the C-terminal end of the Crybb2 gene. Behavioral Q2 phenotyping of these three βB2-mutant lines Crybb2 O377 , Crybb2 Philly , and Crybb2 Aey2 included assessment of exploratory activity and anxiety-related behavior in the open field, sensorimotor gating measured by prepulse inhibition (PPI) of the acoustic startle reflex, cognitive performance measured by social discrimination, and spontaneous alternation in the Y-maze. In each mutant line, we also quantified the number of parvalbumin-positive (PV+) GABAergic interneurons in selected brain regions that express CRYBB2. While there were allele-specific differences in individual behaviors and affected brain areas, all three mutant lines exhibited consistent alterations in PPI that paralleled alterations in the PV+ cell number in the thalamic reticular nucleus (TRN). The direction of the PPI change mirrored that of the TRN PV+ cell number thereby suggesting a role for TRN PV+ cell number in modulating PPI. Moreover, as both altered PPI and PV+ cell number are schizophrenia-associated endophenotypes, our result implicates mutated Crybb2 in the development of this neuropsychiatric disorder. Keywords Crybb2. Schizophrenia. Parvalbumin. Prepulse inhibition (PPI). Thalamic reticular nucleus (TRN) mouse brain function [1-3]. Although molecular mechanisms 33 of Crybb2 lens fiber and epithelial cell activity are established, 34 work continues on mouse brain pleiotropic effects [4, 5]. As 35 βγ-crystallins constitute a separate class of Ca 2+-binding Electronic supplementary material The online version of this article (

Polymorphisms in CRYBB2 encoding βB2-crystallin are associated with antisaccade performance and memory function

“…Although sensorimotor gating alterations are typical symptoms in schizophrenia patients 47 and in patients with schizotypal personality disorder, which is believed to belong to the schizophrenia spectrum 48 , our findings reveal no schizophrenia-specific effects, but were found in the combined sample. The results converge with those observed in mice in which alterations of sensorimotor gating, measured as PPI, were the most consistent behavioral findings in the three homozygous mouse mutants 12 . PPI is largely regulated by neuronal connections between the limbic cortex (including the entorhinal cortex, hippocampus and amygdala), ventral striatum, ventral pallidum and the pontine tegmentum 49,50 .…”

“…Compared to wildtype mice, O377 mutants displayed a decreased acoustic startle reflex (ASR) in combination with an increased prepulse inhibition (PPI). A recently published study confirmed alterations of sensorimotor gating (PPI) in both sexes in all 3 mouse mutant lines 12 . In addition, altered numbers of parvalbumin-positive interneurons were observed in the thalamic reticular nucleus (TRN) of these mice, which is consistent with results showing that a deficiency of parvalbumin, a calcium binding protein, is known to affect PPI 13 .…”

“…As alterations of the PPI were also found in Crybb2 mutant mice 12 , we studied the association between genetic polymorphisms in the CRYBB2 gene and sensorimotor gating in humans. A subset of 352 subjects (109 patients, 243 healthy volunteers) participated in P50 event-related potential assessments.…”

A truncating Aspm allele leads to a complex cognitive phenotype and region-specific reductions in parvalbuminergic neurons

“…DCX+ and PV+ cell numbers were estimated in specific regions of interest (ROIs) with design-based stereology using the Stereo Investigator software system (StereoInvestigator, MBF Biosciences Inc.) on every sixth serial 40 µm coronal section with the Optical Fractionator probe as described previously 22,23 . The observer was blind to the experimental groups during analysis.…”

“…These included the hippocampal dentate gyrus, Cornu Ammonis (CA) 1, 2/3 regions and the anterior cingulate cortex (ACC). We also quantified the PV+ cell number in the thalamic reticular nucleus (TRN) because of the dense PV+ cell population here and our previous evidence that it may play a role in NDD endophenotypes 23 . Volumetric analysis of selected ROIs was performed using the Cavalieri estimator probe as described previously 22 .…”