Developmental expression profile of quaking, a candidate gene for schizophrenia, and its target genes in human...

Decreased expression of oligodendrocyte/myelin-related (OMR) genes, including quaking (QKI), is a consistent finding in gene expression studies of post-mortem brain from subjects with schizophrenia, and these changes are most prominent in the hippocampus vs. the prefrontal cortex (PFC). Although expression of QKI and other OMR genes has been examined in rodents, little is known about their developmental trajectory in the human brain. Therefore, we examined expression of QKI and several putative mRNA targets of QKI in human PFC and hippocampus at different ages. The pattern of QKI expression in the PFC resembled that reported in rodents, with high QKI-5 in the fetal brain and an increase in QKI-6 and QKI-7 during the period of active myelination, although QKI-5 expression did not decrease substantially during postnatal development in the PFC in humans as it does in rodent brain. Most of the putative QKI target genes also showed linear increases in expression with increasing age in the PFC. In contrast, expression of these genes showed little evidence of developmental regulation in the hippocampus. Correlations between expression levels of the nuclear vs. cytoplasmic QKI isoforms, and putative splicing targets of the former, also differed between tissues. Thus, we speculate that a robust increase in OMR gene expression normally occurs with age in the PFC, but not in the hippocampus, which may explain why decreases in OMR gene expression in schizophrenia are more pronounced in the latter tissue. We also suggest that OMR transcripts might be processed by different splicing proteins in different tissues.