RESUMO
The formation of complex dendritic arbors is crucial for the assembly of functional networks as abnormal dendrite formation underlies several neurodevelopmental and psychiatric disorders. Many extracellular factors have been postulated as regulators of dendritic growth. Wnt proteins play a critical role in neuronal development and circuit formation. We previously demonstrated that Wnt7b acts through the scaffold protein dishevelled 1 (Dvl1) to modulate dendrite arborisation by activating a non-canonical Wnt signalling pathway. Here, we identify the seven-transmembrane frizzled-7 (Fz7, also known as FZD7) as the receptor for Wnt7b-mediated dendrite growth and complexity. Importantly, Fz7 is developmentally regulated in the intact hippocampus, and is localised along neurites and at dendritic growth cones, suggesting a role in dendrite formation and maturation. Fz7 loss-of-function studies demonstrated that Wnt7b requires Fz7 to promote dendritic arborisation. Moreover, in vivo Fz7 loss of function results in dendritic defects in the intact mouse hippocampus. Furthermore, our findings reveal that Wnt7b and Fz7 induce the phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and JNK proteins, which are required for dendritic development. Here, we demonstrate that Wnt7b-Fz7 signals through two non-canonical Wnt pathways to modulate dendritic growth and complexity.
Assuntos
Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Dendritos/metabolismo , Hipocampo/crescimento & desenvolvimento , MAP Quinase Quinase 4/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Proteínas Wnt/metabolismo , Animais , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/genética , Dendritos/enzimologia , Dendritos/genética , Proteínas Desgrenhadas/genética , Proteínas Desgrenhadas/metabolismo , Receptores Frizzled , Hipocampo/metabolismo , MAP Quinase Quinase 4/genética , Camundongos , Camundongos Endogâmicos C57BL , Neuritos/metabolismo , Ligação Proteica , Proteínas Proto-Oncogênicas/genética , Ratos , Ratos Wistar , Receptores Acoplados a Proteínas G/genética , Proteínas Wnt/genética , Via de Sinalização WntRESUMO
Initial axonal elongation is essential for neuronal polarization and requires polarized activation of IGF-1 receptors (IGF-1r) and the phosphatidylinositol 3 kinase (PI3k) pathway. Wingless-type family growth factors (Wnts) have also been implied in the regulation of axonal development. It is not known, however, if Wnts have any participation in the regulation of initial axonal outgrowth and the establishment of neuronal polarity. We used cultured hippocampal neurons and growth cone particles (GCPs) isolated from fetal rat brain to show that stimulation with the wingless family factor 3A (Wnt3a) was sufficient to promote neuronal polarization in the absence of IGF-1 or high insulin. We also show that Wnt3a triggered a strong activation of IGF-1r, PI3k, and Akt in developmental Stage 2 neurons and that the presence of activatable IGF-1r and PI3k activation were necessary for Wnt3a polarizing effects. Surface plasmon resonance (SPR) experiments show that Wnt3a did not bind specifically to the IGF-1r. Using crosslinking and immuno-precipitation experiments, we show that stimulation with Wnt3a triggered the formation of a complex including IGF-1r-Wnt3a-Frizzled-7. We conclude that Wnt3a triggers polarization of neurons via cross-activation of the IGF-1r/PI3k pathway upon binding to Fz7.