Wen-Sung Lai

Evidence that the gene encoding ZDHHC8 contributes to the risk of schizophrenia.

Using a relatively dense genetic map of 72 single-nucleotide polymorphisms (SNPs) distributed across the entire 1.5-Mb locus on chromosome 22q11 associated with susceptibilit to schizophrenia, we previously identified two subregions that were consistently associated with the disease. In the distal subregion, we detected an association signal with five neighboring SNPs distributed over a haplotypic block of 80 kb encompassing six known genes. One of these five SNPs, rs175174, had the strongest association of all 72 SNPs that we tested. Here we show that rs175174 regulates the level of the fully functional transcript by modulating the retention of intron 4 of the gene ZDHHC8, which encodes a putative transmembrane palmitoyltransferase. Zdhhc8-knockout mice had a sexually dimorphic deficit in prepulse inhibition, a gene dosage–dependent decrease in exploratory activity in a new environment and a decreased sensitivity to the locomotor stimulatory effects of the psychomimetic drug dizocilpine (MK801). SNP rs175174 shows differences in transmission distortion between sexes in individuals with schizophrenia. Our results indicate that there is an unexpected connection between impaired palmitate modification of neuronal proteins and the psychiatric phenotypes associated with microdeletions of chromosome 22q11.

Transcriptional and behavioral interaction between 22q11.2 orthologs modulates schizophrenia-related phenotypes in mice

Microdeletions of 22q11.2 represent one of the highest known genetic risk factors for schizophrenia. It is likely that more than one gene contributes to the marked risk associated with this locus. Two of the candidate risk genes encode the enzymes proline dehydrogenase (PRODH) and catechol-O-methyltransferase (COMT), which modulate the levels of a putative neuromodulator (L-proline) and the neurotransmitter dopamine, respectively. Mice that model the state of PRODH deficiency observed in humans with schizophrenia show increased neurotransmitter release at glutamatergic synapses as well as deficits in associative learning and response to psychomimetic drugs. Transcriptional profiling and pharmacological manipulations identified a transcriptional and behavioral interaction between the Prodh and Comt genes that is likely to represent a homeostatic response to enhanced dopaminergic signaling in the frontal cortex. This interaction modulates a number of schizophrenia-related phenotypes, providing a framework for understanding the high disease risk associated with this locus, the expression of the phenotype, or both.

Akt1 deficiency affects neuronal morphology and predisposes to abnormalities in prefrontal cortex functioning

There is accumulating evidence that AKT signaling plays a role in the pathogenesis of schizophrenia. We asked whether Akt1 deficiency in mice results in structural and functional abnormalities in prefrontal cortex (PFC). Exploratory transcriptional profiling revealed concerted alterations in the expression of PFC genes controlling synaptic function, neuronal development, myelination, and actin polymerization, and follow-up ultrastructural analysis identified consistent changes in the dendritic architecture of pyramidal neurons. Behavioral analysis indicated that Akt1-mutant mice have normal acquisition of a PFC-dependent cognitive task but abnormal working memory retention under neurochemical challenge of three distinct neurotransmitter systems. Thus, Akt1 deficiency creates a context permissive for gene–gene and gene–environment interactions that modulate PFC functioning and contribute to the disease risk associated with this locus, the severity of the clinical syndrome, or both.

Recognition of Familiar Individuals in Golden Hamsters: A New Method and Functional Neuroanatomy

The ability to recognize individuals is essential for many aspects of social interaction and social organization, yet we know relatively little about the neural mechanisms underlying this ability. Most laboratory studies of individual recognition in rodents have studied differential responses to familiar versus unfamiliar individuals rather than differential responses to equally well known individuals having different significance for the subject. In experiment 1, we use a new method for studying true individual recognition in which male hamsters first had different experiences with two stimulus males (exposures to one male across a wire-mesh barrier and fights with another male). One day later, losers of fights were tested in a Y-maze for reactions to one of the two familiar males. Subjects tested with the familiar winner avoided this stimulus male, but subjects tested with the familiar, neutral male were attracted to him. Immunohistochemistry for c-Fos and Egr-1 implicate several areas of the brain in individual recognition, particularly the anterior piriform cortex, the CA1 and CA3 regions of anterior dorsal hippocampus, anterior and posterior dentate gyrus, and perirhinal cortex. In experiment 2, temporary inactivation of the CA1 region of anterior dorsal hippocampus by microinfusion of lidocaine eliminated the avoidance of the familiar winner, but a saline control injection had no effect. These results are the first to use a rodent model to characterize neural circuits involved in the recognition of equally well known individuals and the corresponding emotional responses to them.

Nogo Receptor 1 (RTN4R) as a Candidate Gene for Schizophrenia: Analysis Using Human and Mouse Genetic Approaches

Background NOGO Receptor 1 (RTN4R) regulates axonal growth, as well as axon regeneration after injury. The gene maps to the 22q11.2 schizophrenia susceptibility locus and is thus a strong functional and positional candidate gene. Methodology/Principal Findings We evaluate evidence for genetic association between common RTN4R polymorphisms and schizophrenia in a large family sample of Afrikaner origin and screen the exonic sequence of RTN4R for rare variants in an independent sample from the U.S. We also employ animal model studies to assay a panel of schizophrenia-related behavioral tasks in an Rtn4r-deficient mouse model. We found weak sex-specific evidence for association between common RTN4R polymorphisms and schizophrenia in the Afrikaner patients. In the U.S. sample, we identified two novel non-conservative RTN4R coding variants in two patients with schizophrenia that were absent in 600 control chromosomes. In our complementary mouse model studies, we identified a haploinsufficient effect of Rtn4r on locomotor activity, but normal performance in schizophrenia-related behavioral tasks. We also provide evidence that Rtn4r deficiency can modulate the long-term behavioral effects of transient postnatal N-methyl-D-aspartate (NMDA) receptor hypofunction. Conclusions Our results do not support a major role of RTN4R in susceptibility to schizophrenia or the cognitive and behavioral deficits observed in individuals with 22q11 microdeletions. However, they suggest that RTN4R may modulate the genetic risk or clinical expression of schizophrenia in a subset of patients and identify additional studies that will be necessary to clarify the role of RTN4R in psychiatric phenotypes. In addition, our results raise interesting issues about evaluating the significance of rare genetic variants in disease and their role in causation.

Distribution of large terminal inputs from the primary and secondary somatosensory cortices to the dorsal thalamus in the rodent

The present study was undertaken to determine the precise projection pattern from the primary (S1) and secondary (S2) somatosensory cortices to the posterior nuclear proper (POm) and ventroposterior thalamic nuclei (VP). The POm was previously shown to receive large boutons arising exclusively from layer V of the S1 barrel region. This descending input was proposed to play a key role, namely, as a driver, in shaping the receptive property of POm neurons. To determine whether other body parts and the S2 also contribute such unique inputs to the dorsal thalamus, anterograde neuroanatomical tracers were focally deposited in the S1 and S2 forepaw and whisker regions of rats and C57BL6‐Tg (GFPm)/Thy1 transgenic mice. Our major findings were that, 1) irrespective of body representations, both the S1 and the S2 provided corticothalamic large terminals to the POm with comparable morphological characteristics and 2) descending large terminals were also noted in particular subzones within the VP, including boundary and caudal areas. We concluded, based on these findings, that the rodent VP has three partitions: the rostral VP innervated by small corticothalamic terminals, the caudal VP with both corticothalamic small and large terminals, and a surrounding shell region, which also contained large terminals. Furthermore, assuming that the large terminal has a drivers role, we propose that particular subzones in the VP may play a role as a multiple‐order thalamic relay so that they can simultaneously coordinate with first‐ and higher‐order relays in the thalamocortical circuitry for processing somatosensory information. J. Comp. Neurol. 518:2592–2611, 2010.

Behavioral phenotyping of v-akt murine thymoma viral oncogene homolog 1-deficient mice reveals a sex-specific prepulse inhibition deficit in females that can be partially alleviated by glycogen synthase kinase-3 inhibitors but not by antipsychotics

Schizophrenia is a severe mental illness with a strong genetic predisposition. Accumulating evidence from human genetics and animal studies suggest v-akt murine thymoma viral oncogene homolog 1 (Akt1) might contribute to susceptibility for schizophrenia. In contrast to inconclusive findings in human genetic studies, a mutant mouse model is a simplified and alternative approach to determining the biological functions of AKT1 and its possible role in the pathogenesis of schizophrenia. In study 1, a comprehensive battery of behavioral tests was performed on both male and female mice. The results of behavioral phenotyping did not reveal significant differences between genotypes or sexes, except increased time of immobility in the tail suspension test and acoustic prepulse inhibition (PPI) deficits in Akt1-knockout females. On the basis of the observed PPI deficit, in study 2a, neuromorphological alterations were examined with morphometric analysis of green fluorescent protein (GFP)-labeled pyramidal neurons in the auditory cortex of female mice. The results indicated abnormalities in the architecture and complexity of the neurons of mutant females compared with those of the controls. In study 2b, potentially effective pharmacological treatments were explored to mitigate the observed PPI deficits in females. Antipsychotics (either raclopride (3 mg/kg) or clozapine (3 mg/kg)) did not alleviate observed PPI deficits in Akt1-knockout females but it was partially normalized by 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT, 5 mg/kg) and SB216763 (2.5 mg/kg). These findings imply the importance of AKT1 in some behavioral phenotypes and dendritic morphology in the auditory cortex of female mice, and they also suggest that subjects with Akt1 deficiency are insensitive to antipsychotic drugs, whereas glycogen synthase kinase-3 (GSK3) inhibitors could have therapeutic potential for the treatment of acoustic PPI deficits.

Patterns of neural activation associated with exposure to odors from a familiar winner in male golden hamsters

The neural mechanisms underlying recognition of familiar individuals and responses appropriate to them are not well known. Previous studies with male golden hamsters have shown that, after a series of brief aggressive encounters, a loser selectively avoids his own, familiar winner but does not avoid other males. Using this paradigm, we investigated activity in 20 areas of the brain using immunohistochemistry for c-Fos and Egr-1 during exposure to a familiar winner compared to control groups not exposed to another male. Behavioral data showed that 1 day after fights males that lost avoided the familiar winner, suggesting that they recognized this individual. The c-Fos and Egr-1 immunohistochemistry showed that the losers exposed to familiar winners had a greater density of stained cells in the basolateral amygdala, the CA1 region of anterior dorsal hippocampus and the dorsal subiculum than control groups had in these areas. These results suggest that these brain areas may be involved in the memory for other males, the learned fear of familiar winners, or related processes.

Phenotypic characterization of C57BL/6J mice carrying the Disc1 gene from the 129S6/SvEv strain

Disruption of disrupted-in-schizophrenia 1 (DISC1), a candidate susceptibility gene for schizophrenia, was first identified in a large Scottish family in which many members suffered from various psychiatric disorders, including schizophrenia. To model the Scottish DISC1 truncation, we established a Disc1 mutant mouse line in which the 129S6/SvEv 25-bp deletion variant was transferred into the C57BL/6J strain by backcrossing. A battery of behavioral tasks was conducted to evaluate the basic behaviors and cognitive function of these mice. In heterozygote and homozygote Disc1 mutant (Het and Homo) mice, behavioral impairments were noted in working memory test which is thought to be mediated by the function of the medial prefrontal cortex (mPFC). The properties of mPFC neurons were characterized in both morphological and physiological aspects. The dendritic diameters were decreased in layer II/III mPFC pyramidal neurons of Het and Homo mice, whereas a significant reduction in spine density was observed in Homo mice. Neuronal excitability was declined in layer II/III mPFC pyramidal neurons of Het and Homo mice, yet increased transmitter release was identified in Homo mice. Thus, the structural and functional alterations of the mPFC in Het and Homo mice might account for their cognitive impairment. Since most of the gene knockout mice are generated from 129 substrain-derived embryonic stem cells, potential Disc1 deficiency should be considered.

Distinct phenotypes of new transmembrane-domain neuregulin 1 mutant mice and the rescue effects of valproate on the observed schizophrenia-related cognitive deficits

Accumulating evidence suggests that neuregulin 1 (NRG1) might be involved in the neurodevelopment, neural plasticity, GABAergic neurotransmission, and pathogenesis of schizophrenia. NRG1 is abundantly expressed in the hippocampus, and emerging studies have begun to reveal the link between NRG1 signaling and cognitive deficits in schizophrenic patients. Because the transmembrane domain of NRG1 is vital for both forward and reverse signaling cascades, new Nrg1-deficient mice that carry a truncation of the transmembrane domain of the Nrg1 gene were characterized and used in this study to test a NRG1 loss-of-function hypothesis for schizophrenia. Both male and female Nrg1 heterozygous mutant mice and their wild-type littermates were used in a series of 4 experiments to characterize the impact of Nrg1 on behavioral phenotypes and to determine the importance of Nrg1 in the regulation of hippocampal neuromorphology and local GABAergic interneurons. First, a comprehensive battery of behavioral tasks indicated that male Nrg1-deficient mice exhibited significant impairments in cognitive functions. Second, pharmacological challenges were conducted and revealed that Nrg1 haploinsufficiency altered GABAergic activity in males. Third, although no genotype-specific neuromorphological alterations were found in the hippocampal CA1 pyramidal neurons, significant reductions in the hippocampal expressions of GAD67 and parvalbumin were revealed in the Nrg1-deficient males. Fourth, chronic treatment with valproate rescued the observed behavioral deficits and hippocampal GAD67 reduction in Nrg1-deficient males. Collectively, these results indicate the potential therapeutic effect of valproate and the importance of Nrg1 in the regulation of cognitive functions and hippocampal GABAergic interneurons, especially in males.