Abstract
The development of polarized hippocampal neurons with a single axon and multiple dendrites depends on the activity of phosphoinositide 3-kinase (PI3K) and the GTPase Rap1B. Here we show that PI3K regulates axon specification and elongation through the GTPase Rheb and its target mammalian target of rapamycin (mTOR). Overexpression of Rheb induces the formation of multiple axons, whereas its suppression by RNA interference blocks axon specification. mTOR is a central regulator of translation that phosphorylates eIF4E-binding proteins like 4E-BP1. Axon formation was suppressed by inhibition of mTOR and expression of mTOR-insensitive 4E-BP1 mutants. Inhibition of PI3K or mTOR reduced the level of Rap1B, which acts downstream of Rheb and mTOR. The ubiquitin E3 ligase Smurf2 mediates the restriction of Rap1B by initiating its degradation. Suppression of Smruf2 by RNA interference is able to compensate the loss of Rheb. These results indicate that the mTOR pathway is required to counteract the Smurf2-initiated degradation of Rap1B during the establishment of neuronal polarity.
Highlights
We show that Rheb and the phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway are required for the specification and elongation of axons and act upstream of Rap1B
We first tested whether insulin is able to induce supernumerary axons because it activates the mTOR pathway in many cell types including neurons and its receptor is present in all neurites [18, 21, 42]
Our results show that Rheb and mTOR pathways are required for the establishment of neuronal polarity and act through Rap1B
Summary
We show that Rheb and the PI3K/mTOR pathway are required for the specification and elongation of axons and act upstream of Rap1B. Rheb Acts Downstream of PI3K and Upstream of mTOR to Specify Axons—To test if activation of mTOR has an effect on axon formation, we transfected hippocampal neurons with an expression vector for Rheb. We first tested whether insulin is able to induce supernumerary axons because it activates the mTOR pathway in many cell types including neurons and its receptor is present in all neurites [18, 21, 42].
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have