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 1,2 , we previously identified two subregions that were consistently associated with the disease 3,4 . 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 4 . 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.SNP rs175174 is located in intron 4 of ZDHHC8 (previously annotated as KIAA1292; Fig. 1a,b), and the potential effect of rs175174 genotype on splicing warranted further investigation. We prepared total or poly(A) + RNA from fresh (nontransformed) human lymphocytes and subjected it to reverse transcription, PCR amplification using primers located in exons 1 and 8 and sequencing. This analysis identified a reproducible, complex pattern of alternative splicing around intron 4 (similar analysis of exons 8-11 showed no evidence for alternative splicing; data not shown). We identified two main products of comparable abundance in both the total (Fig. 1c) and the poly(A) + RNA fractions (data not shown), derived either from the fully spliced form or from an unspliced form retaining intron 4 (Fig. 1c). Sequence analysis of the introns and their flanking regions identified a suboptimal 5′ splice site (Fig. 1b) that could reduce the efficiency of splicing, leading to the retention of intron 4 (refs. 5,6). Examples of intron retention have been found in transcripts from several species 7 . SNP rs175174 is located in the middle of intron 4, embedded in a highly conserved heptanucleotide motif (Fig. 1d). The retained intron introduces a stop codon in the open reading frame that could lead to premature termination of translation (Fig. 1d).We constructed minigenes from the 'risk' and 'nonrisk' alleles containing exon 4, intron 4 and exon 5 along with flanking genomic sequences and transfected them into human embryonic kidney (HEK293) cells. Initial semiquantitative PCR amplification analysis showed that the pattern of splicing observed in lymphocytes was recapitulated in total RNA prepared from HEK293 cells transiently...

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.

SUMMARY Individuals with 22q11.2 microdeletions have cognitive deficits and a high risk of developing schizophrenia. Here, we provide evidence that primary hippocampal neurons from a 22q11.2 deletion mouse model [Df(16)A+/−] have decreased density of dendritic spines and glutamatergic synapses, as well as impaired dendritic growth. These deficits can be prevented by introduction of enzymatically active ZDHHC8 palmitoyltransferase encoded by a gene located in the 22q11.2 locus and they are also observed in primary cultures from Zdhhc8-deficient mice. We show that many of these deficits are also present in the hippocampus of adult Df(16)A+/− and Zdhhc8-deficient mice. Finally, we provide evidence that PSD95 is one of the substrates of ZDHHC8. Our analysis reveals that 22q11.2 microdeletion results in deficits in neuronal development and suggests that impaired neuronal protein palmitoylation contributes to many of these deficits.

The low affinity neurotrophin receptor p75NTR can mediate cell survival as well as cell death of neural cells by NGF and other neurotrophins. To elucidate p75NTR-mediated signal transduction, we screened p75NTR-associated proteins by a yeast two-hybrid system. We identified one positive clone and named NADE (p75NTR-associated cell death executor). Mouse NADE has marked homology to the human HGR74 protein. NADE specifically binds to the cell-death domain of p75NTR. Co-expression of NADE and p75NTR induced caspase-2 and caspase-3 activities and the fragmentation of nuclear DNA in 293T cells. However, in the absence of p75NTR, NADE failed to induce apoptosis, suggesting that NADE expression is necessary but insufficient for p75NTR-mediated apoptosis. Furthermore, p75NTR/ NADE-induced cell death was dependent on NGF but not BDNF, NT-3, or NT-4/5, and the recruitment of NADE to p75NTR (intracellular domain) was dose-dependent. We obtained similar results from PC12 cells, nnr5 cells, and oligodendrocytes. Taken together, NADE is the first signaling adaptor molecule identified in the involvement of p75NTR-mediated apoptosis induced by NGF, and it may play an important role in the pathogenesis of neurogenetic diseases.

Several neuropsychiatric disorders are associated with cognitive and social dysfunction. Post-mortem studies of patients with schizophrenia have revealed specific changes in area CA2, a long over-looked region of the hippocampus recently found to be critical for social memory formation. To examine how area CA2 is altered in psychiatric illness, we used the Df(16)A+/− mouse model of the 22q11.2 microdeletion, a genetic risk factor for developing several neuropsychiatric disorders, including schizophrenia. We report several age-dependent CA2 alterations: a decrease in the density of parvalbumin-stained interneurons, a reduction in the amount of feed-forward inhibition and a change in CA2 pyramidal neuron intrinsic properties. Furthermore, we found that area CA2 is less plastic in Df(16)A+/− mice, making it nearly impossible to evoke action potential firing in CA2 pyramidal neurons. Finally, we show that Df(16)A+/− mice display impaired social cognition, providing a potential mechanism and a neural substrate for this impairment in psychiatric disorders.