The autophagy-related kinase UNC-51 and its binding partner UNC-14 regulate the subcellular localization of the Netrin receptor UNC-5 inCaenorhabditis elegans

Ken-ichi Ogura,Yoshio Goshima

doi:10.1242/dev.02503

Abstract

UNC-51 and UNC-14 are required for the axon guidance of many neurons in Caenorhabditis elegans. UNC-51 is a serine/threonine kinase homologous to yeast Atg1, which is required for autophagy. The binding partner of UNC-51, UNC-14, contains a RUN domain that is predicted to play an important role in multiple Ras-like GTPase signaling pathways. How these molecules function in axon guidance is largely unknown. Here we observed that, in unc-51 and unc-14 mutants, UNC-5, the receptor for axon-guidance protein Netrin/UNC-6, abnormally localized in neuronal cell bodies. By contrast, the localization of many other proteins required for axon guidance was undisturbed. Moreover, UNC-5 localization was normal in animals with mutations in the genes for axon guidance proteins, several motor proteins, vesicle components and autophagy-related proteins. We also found that unc-5 and unc-6 interacted genetically with unc-51 and unc-14 to affect axon guidance, and that UNC-5 co-localized with UNC-51 and UNC-14 in neurons. These results suggest that UNC-51 and UNC-14 regulate the subcellular localization of the Netrin receptor UNC-5, and that UNC-5 uses a unique mechanism for its localization; the functionality of UNC-5 is probably regulated by this localization.

Highlights

IntroductionNewborn neurons extend axons to precise targets (other neurons or muscle), and form synapses on them
Newborn neurons extend axons to precise targets, and form synapses on them
We speculated that UNC-51 and UNC-14 might regulate the localization of molecules required for DD/VD axon guidance, probably by vesicle trafficking, for the following reasons: (1) mutants of unc-51 and unc-14 have defects in DD/VD axon guidance (McIntire et al, 1992) (Fig. 1C,D); (2) Atg1, a yeast homolog of UNC-51, is required for autophagy (Matsuura et al, 1997; Straub et al, 1997); (3) UNC-14 has a RUN domain, which is predicted to play important roles in the Rap and Rab family GTPase signaling pathways for vesicle trafficking (Callebaut et al, 2001); (4) unc-51 and unc-14 are expressed in DD/VD neurons (Ogura et al, 1997)

Summary

Introduction

Newborn neurons extend axons to precise targets (other neurons or muscle), and form synapses on them. Two C. elegans Netrin receptors, UNC-5 and UNC-40 (mammalian DCC homolog), are known (Chan et al, 1996; Leung-Hagesteijn et al, 1992) Both belong to the immunoglobulin superfamily, have a single transmembrane domain and are expressed in neurons that respond to Netrin (Chan et al, 1996; Su et al, 2000). Both UNC-5 and UNC-40 are required for dorsally extending axons to be repulsed by ventral Netrin (Hedgecock et al, 1990; McIntire et al, 1992). Netrin binds the Ig domain of UNC-5, and the fibronectin type III domain of UNC-40/DCC (Kruger et al, 2004)

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Conclusion