Molecular characterization of the conditional deletion of Vesicular Aminergic-Associated Transporter (VAAT / SLC10A4) in serotonergic neurons of adult mice

Abstract

The orphan transporter, Vesicular Aminergic – Associated Transporter (VAAT/SLC10A4) was recently shown to have a modulatory role in monoaminergic and cholinergic signalling systems. These studies used constitutive knockout mice (VAAT KO) and revealed that some effects of the VAAT KO are obscured by compensatory changes. Moreover, VAAT deletion might exert different effects in different aminergic neurons. Hence, for the proper understanding of the function of VAAT, its effect on individual aminergic brain nuclei should be studied separately. Here, we have generated and characterised a conditional allele of VAAT gene for implementing the conditional knockout strategy. We used the tamoxifen-inducible CreERT2 (SERTCreERT2) to spatio-temporally restrict the VAAT knockout in the serotonergic neurons of adult mice. Detailed analysis revealed that SERTCreERT2 has background activity in the absence of tamoxifen resulting in 35.3% VAAT knockout in SERTCreERT2/+; VAATlox/ko animals. After tamoxifen administration, a very specific and complete deletion of VAAT was observed in the raphe nuclei, thus confirming the inducible (64.7%) and conditional deletion of VAAT (VAATicKO). Furthermore, no compensatory changes in the transcript levels of serotonergic genes were observed in VAATicKO either under normal or stressful situations. Finally, preliminary results indicate higher brain serotonin levels in VAATicKO mice under stress when compared to control (P=0.0926) while no difference was observed under normal conditions. This observation could now be further explored to validate the role of VAAT in serotonin homeostasis.