Downregulation of TPH1 or rather TPH2 by stable transfection of adult neural stem cells with lentiviral vectors containing sequences for siRNAs

Recent evidence implicates a particular role for the serotonergic system in regulation of adult neurogenesis in a mouse animal model of hippocampus. Serotonin (5-HT) serves as a protector of adult neural stem cell (ANSC) growth. Lack of 5-HT caused by tryptophan-hydroxylase (TPH) depletion leads to a decrease in stem cell proliferation. Both isoforms of TPH (TPH1 and TPH2) are present in undifferentiated ANSC. So far, no reliable TPH1 and TPH2 knockout animal models are available; i.e. TPH2 KO mice are infertile. Therefore, we sought to investigate the influence of different TPH isoforms in-vitro by a selective gene-silencing approach. In addition to the lack of a suitable animal model, we sought to employ the novel technique of RNA interference in order to study TPH 1 and 2 isoforms on the particularly interesting level of adult neurogenesis.

Our system involves oligonucleotides containing the TPH1 or TPH2 siRNA sequence in sense and antisense interrupted by a 9bp loop sequence (5’-TTCAAGAGA–3’) and ClaI and accordingly MluI restriction sites were cloned in the lentiviral vector pLVTHM. The packaging of the vector was obtained as described previously (Dull et al., 1998; Follenzi et al., 2000) by cotransfection of 293T cells with the following constructs: lentivector pLVTHM with siRNA sequence, packaging vector psPAX2, envelope vector pMD2G (vectors kindly provided by Didier Trono, University of Lausanne).