A role of microRNA-29b-mediated β-catenin signaling in the mouse brain development

Abstract

INTRODUCTION: β-catenin has been widely implicated in the regulation of mammalian development and homeostasis. However, in vivo mechanisms by which Wnt/β-catenin signaling components regulate physiological events during brain development remain undetermined. Inhibitor of β-catenin and T cell factor (ICAT) interferes the association of β-catenin with T cell factor. Deficiency of ICAT in mice results in severe malformation of the forebrain and craniofacial bones, suggesting its critical role in regulation of the Wnt signaling in the CNS. The microRNA-29 family is abundantly expressed in the adult cortex, but not in the embryonic brain. However, its physiological role in neuronal development has not been well-studied. The purpose of this study is to determine if deregulated ICAT by miR-29 results in a defective neurogenesis toward neuronal cell lineages and whether these pathologies are due to impaired β-catenin-mediated signaling events. METHODS: To mimic in vivo micro-environment, neural stem cells (NSCs) were cultured in 3D microfluidics device. Then qRT-PCR, BrdU-pulse and immunofluorescence were performed to characterize NSCs stemness in the niche, such as proliferation and self-renewal properties. In addition, luciferase activity was examined whether miR-29b directly targets the 3-untranslated region (3-UTR) of ICAT. Furthermore, in utero electroporation method was applied to investigate the roles of miR-29b in vivo during fetal corticogenesis under technical cooperation with a research lab at Hallym University. RESULTS: miR-29b, but not miR-29a or c, is increased in differentiated NSCs which is reverse-correlated with the decreased levels of ICAT. I also found that miR 29b diminished NSCs proliferation and self-renewal capabilities, and controlled their fate, directing their differentiation along certain cell lineages. A luciferase reporter assay revealed that the 3-UTR of the ICAT mRNA (also known as CTNNBIP 1 gene) is the direct target of miR-29b. In vivo results show that applied anti-sense miR-29b by in utero electroporation in corticogenesis led to the proliferative defect and premature outward migration. CONCLUSIONS: I showed that miR-29b regulates neurogenesis by controlling Wnt/β-catenin signaling during brain development via inhibition of ICAT expression. Furthermore, these research findings may identify novel therapeutic approaches to modulate ICAT-mediated Wnt/β-catenin signaling to treat or prevent neurological disorders in humans.