| In the nervous system, PI 3-kinase has been implicated in neuronal differentiation. My studies have focused on a candidate neuronal PI 3-kinase target centaurin alpha-1, which binds PtdIns(3,4,5)P3, and is an Arf6 GAP. Centaurin alpha-1 is localized in dendrites, dendritic spines and synapses, and is required for neuronal differentiation and spine morphogenesis. In dissociated neuronal cultures, expression of centaurin alpha-1 enhances dendritic branching, and increases dendritic filopodia, lamellipodia and spine-like protrusions. Expression of centaurin alpha-1 GAP inactive mutant or knocking down centaurin alpha-1 levels using siRNA leads to inhibition of dendritic outgrowth and branching. Manipulations of centaurin alpha-1 also disrupt spine morphogenesis in organotypic brain slice cultures. The effects of centaurin alpha-1 on dendritic development are dependent on it functioning through regulation of Arf6. The constitutively GTP-bound mutant Arf6, which reduces dendritic branching on its own, is able to reverse the effects of centaurin alpha-1 overexpression. Conversely, expression of the GDP-bound mutant, Arf6, which enhances branching and outgrowth on its own, can prevent the loss of dendrites induced by centaurin alpha-1 GAP inactive mutant expression or siRNA knock down. Arf6 has been shown to regulate Rac1, and both Arf6 and centaurin alpha-1 have been proposed to regulate ERK; both Rac1 and ERK have been implicated in neuronal differentiation. Thus, I examined whether centaurin alpha-1 modulates neuronal Rac1 and ERK, to identify candidate downstream effectors of centaurin alpha-1 and Arf6 in neuronal differentiation. ERK and Rac1 activation are enhanced in centaurin alpha-1 over-expressing neurons and this activation is dependent on centaurin alpha-1 GAP activity. As a regulator of Arf6, centaurin alpha-1 has emerged as a candidate to participate in PI 3-kinase regulated Arf6 pathways that control dendritic differentiation and spine morphogenesis. |
