Role of 3ʹUTR in the regulation of neurotrophic factors BDNF and GDNF

During the past decade, 3ʹ untranslated regions (3ʹUTRs) of mRNAs continue to emerge as important sites for gene regulation due to the binding of microRNAs (miRs), RNA-binding proteins (RBPs) and possibly other trans-acting factors. Brain derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) play important roles inside and outside the central nervous system (CNS). Whilst precise spatiotemporal regulation of BDNF and GDNF levels are crucial in determining biological outcome, mechanisms involved in controlling their levels are not fully understood. In this thesis, we investigated the 3ʹUTR mediated regulation of BDNF and GDNF. We demonstrate the presence of regulatory elements in the 3ʹUTR of BDNF and GDNF and, show that BDNF is regulated by 4 different miRs, namely miR-1, miR-10b, miR-155 and miR-191, and by RBP tristetraprolin (TTP) in different cell lines. Further, we show that GDNF is regulated by multiple miRs in cell lines and identify binding sites for miR-146 and miR-96 in the GDNF 3ʹUTR. We demonstrate that in vivo replacement of GDNF 3ʹUTR with a 3ʹUTR with reduced responsiveness to negative regulators including miRs leads to elevated level of endogenous GDNF mRNA and protein in various organs with profound effects on the brain dopaminergic system in mice. We conclude that 3ʹUTR mediated regulation of BDNF and GDNF is biologically important and propose that 3ʹUTR replacement is a highly informative way to study gene function in vivo.