Localized Regulation of Axonal RanGTPase Controls Retrograde Injury Signaling in Peripheral Nerve

Abstract

Summary Peripheral sensory neurons respond to axon injury by activating an importin-dependent retrograde signaling mechanism. How is this mechanism regulated? Here we show that Ran GTPase and its associated effectors RanBP1 and RanGAP regulate the formation of importin signaling complexes in injured axons. A gradient of nuclear RanGTP versus cytoplasmic RanGDP is thought to be fundamental for the organization of eukaryotic cells. Surprisingly, we find RanGTP in sciatic nerve axoplasm, distant from neuronal cell bodies and nuclei, and in association with dynein and importin α. Following injury, localized translation of RanBP1 stimulates RanGTP dissociation from importins and subsequent hydrolysis, thereby allowing binding of newly synthesized importin β to importin α and dynein. Perturbation of RanGTP hydrolysis or RanBP1 blockade at axonal injury sites reduces the neuronal conditioning lesion response. Thus, neurons employ localized mechanisms of Ran regulation to control retrograde injury signaling in peripheral nerve.

Axonal transport of neural membrane protein 35 mRNA increases axon growth

“…For this, we generated a diffusion-limited myristoylated green fluorescent protein (GFP myr ) reporter (Aakalu et al, 2001) carrying the 39UTR of NMP35 mRNA (GFP myr 39NMP35). The myristoylation element in GFP coding sequence decreases its diffusion compared to non-modified GFP such that fluorescence recovery after photobleaching (FRAP) can be used to test for localized translation events by comparing recovery with and without active protein synthesis (Vuppalanchi et al, 2010;Yudin et al, 2008). Without a localizing UTR, the GFP myr mRNA is restricted to the neuronal cell body (Aakalu et al, 2001;Akten et al, 2011;Ben-Yaakov et al, 2012;Perry et al, 2012;Vuppalanchi et al, 2010;Willis et al, 2007;Yudin et al, 2008).…”

“…dendrites), it is now clear that the pre-synaptic or axonal processes also have the capacity to synthesize proteins (Jung et al, 2012). This has been particularly evident in growing axons, both for developing and regenerating axons, but there are several publications supporting the notion that mRNAs and ribosomes are present in mature axons of neurons in the peripheral nervous system (PNS) prior to injury (Ben-Yaakov et al, 2012;Hanz et al, 2003;Koenig et al, 2000;Perlson et al, 2005;Yudin et al, 2008;Zelená, 1970). Studies of cutaneous nerve terminals also suggest that translation of mRNAs can be triggered by pain invoking stimuli (Jimenez-Diaz et al, 2008;Melemedjian et al, 2010).…”

Genomic analysis of RNA localization

“…For example, the appearance of signal in axons on a short timescale (»20 min) is interpreted as evidence that the new signal is due to locally translated GFP. 112,113 Similarly, by converting the fluorescence emitted from photoconvertible GFP molecules from green to red, the appearance of new molecules of protein can be analyzed. This technique has been used to monitor the axonal translation of protein 114 and the retrograde movement of protein from growth cones back toward the cell body.…”

Multifunctional Basic Motif in the Glycine Receptor Intracellular Domain Induces Subunit-specific Sorting

“…Indeed, ␣-karyopherins have been described to mediate transport functions in pre-and postsynaptic compartments of neurons (33)(34)(35)(36). It has been proposed that karyopherin-mediated signaling from the synapse to the nucleus represents a general mechanism for regulation of synaptic plasticity (37).…”