Study Of Neuregulin 1 Gene Expression

Schizophrenia is a severe and disabling mental disorder that affects 1% of population.However, its pathogenic mechanisms remain elusive. Recent genetic studies identifyneuregulin 1 (NRG1) as a susceptibility gene of schizophrenia. NRG1 encodes a family ofEGF-containing growth factors with distinct N-terminal regions, based on which weclassify NRG1 into six types,Ⅰ～Ⅵ. Dozens of single nucleotide polymorphisms (SNPs)have been identified in the NRG1 gene, some of which correlate with clinic symptoms.Because most SNPs are located in the introns or 5' untranslated region (UTR), they arethought to regulate the expression of the gene. Indeed, typeⅠandⅣisoform of NRG1 wasincreased at mRNA levels in the prefrontal cortex of schizophrenic patients (Law, A. J. etal. 2006, Proc. Natl. Acad. Sci. USA 103, 6747-6752). Nevertheless, whether and how theexpression of NRG1 isoforms are regulated by unique mechanisms remains unknown. Wehave obtained human BAC clones to investigate mechanisms that control isoform-specificexpression. We have compared protein sequences and 5' UTR DNA sequences of typeⅠ～ⅤNRG1 between different species, and found that they are highly Conserved, which suggestthat we can use rodent models to study NRG1 expression mechanism. Here, firstly, weconfirmed that mRNA of typeⅠ～ⅤNRG1 do exist in rat brain and can be regulated byneuronal activity. Secondly, we report results of initial characterizations of the 5'UTRpromoter activity of TypeⅠ,ⅢandⅣNRG1. DNA sequences immediately upstream of thetranslation initiation sites were amplified by PCR using as template the BAC clone(RoswellPark Cancer Institute) and subcloned into pGL2 at the upstream of the firefly luciferasegene. NRG1-pGL2 constructs were co-transfected with pRL-TK thatexpresses Renilla luciferase under the control of the thymidine kinase promoter. Neuronalactivity can up regulate typeⅠandⅣNRG1 and down regulate typeⅢNRG1. And wescreened for intracellular pathways that could stimulate NRG1 expression. Results suggest that the expression of TypeⅠ, but not TypeⅢorⅣ, NRG1 was increased by co-expressionofβ-catenin in human neuroblastoma SH-SY5Y cells, which can be inhibited by overexpress domain negative (DN) TCF/LEF.These results identify potential mechanisms thatcontrol expression of distinct NRG1 isoforms. Experiments are underway to investigatepathways upstream and downstream ofβ-catenin and neuronal activity. Our studies maycontribute to a better understanding of abnormal expression of NRG1 isoforms inschizophrenic brain regions. Schizophrenia is a debilitating mental disorder that affects 1% of population. However,its pathogenic mechanisms remain elusive. Recent genetic studies identify neuregulin 1(NRG1) as a susceptibility gene of schizophrenia. Dozens of studied indicate abnormalexpression of neuregulin 1 (NRG1) may play a role in pathology of Schizophrenia. Theresults we have showed in first part identified that NRG1 is regulated by multiple promoterswhich drive different types of NRG1 expression under different mechanism. Others' studyalso showed that typeⅣisoform of NRG1 was increased at mRNA levels in the prefrontalcortex of schizophrenic patients. And human typeⅣNRG1 specifically express in brain.And the results in first part indicate that typeⅣNRG1 really exist in rat brain. But analysisof cDNA sequence indicates that there is no similar translation initial site in rat or mousetypeⅣNRG1 compare to that of human. If there is no functional translation initial site inrat or mouse typeⅣNRG1 cDNA, there will be no functional typeⅣNRG1, whichmeans rodent animals are not good to study expression regulation or function of typeⅣNRG1. In this study, we firstly found potential alternate translation initial site in rat typeⅣNRG1 cDNA. Then, we made construct which contain rat typeⅣNRG1 cDNA, andconfirmed that it can express NRG1. Second, we report here that typeⅣNRG1 can be upregulated by neuronal activity, and CREB played a role in this process. In summary, weconfirmed that typeⅣNRG1 can be expressed in rat, which indicates that rodent animalsare good to establish NRG1 models for Schizophrenia; and we identifed one of mechanismsthat regulate typeⅣNRG1 expression. All of these will help us to understand NRG1 andSchizophrenia further.