Axon Guidance

A Motor for Netrin Receptors

Science's STKE  13 Feb 2007:
Vol. 2007, Issue 373, pp. tw47
DOI: 10.1126/stke.3732007tw47

Netrin receptors include neogenin and DCC (deleted in colorectal cancer). These receptors function in axon guidance, with neogenin implicated in the response to repulsive guidance cues and DCC in the response to attractive guidance cues. Myosin X (Myo X) is an unconventional myosin implicated in the formation of cellular projections. Zhu et al. found that Myo X interacted with neogenin and DCC in a manner that required the FERM domain of Myo X and the P3 region of the netrin receptor. Neogenin interacted more strongly with Myo X lacking the motor domain, whereas DCC showed a preference for full-length Myo X. (A motorless form of Myo X generated by alternative splicing has been reported in brain.) Overexpression studies in COS7 cells, rat cortical neurons, and the neuronal cell line NLT suggested that Myo X and DCC colocalized at the tips of filopodia and that Myo X increased the delivery of DCC to these structures. RNA interference studies to knock down Myo X in NLT cells showed that, in the absence of endogenous Myo X, DCC targeting to neurites was decreased (based on immunofluorescence analysis). NLT cells exhibited opposing responses to netrin depending on whether MyoX was coexpresssed with neogenin or DCC. Netrin treatment of the DCC- and Myo X-expressing cells resulted in the formation of neurites and a neuronal-like morphology, whereas the neogenin- and Myo X-expressing cells adopted a spread morphology lacking filopodia or neurites. The motorless Myo X was overexpressed in mouse embryos using in utero electroporation, and the response of cortical explants from these mice to netrin was analyzed. The neurons expressing the motorless Myo X showed shorter neurites in the absence of netrin and reduced outgrowth in response to netrin. In ovo electroporation of the motorless Myo X allowed the effect of Myo X on commissural axon guidance to be analyzed in chicken embryos. Neurons expressing the motorless Myo X failed to cross the midline. This study demonstrates a direct association between a motor protein, Myo X, and the plasma membrane netrin receptors. Furthermore, the differential interaction of neogenin with a motorless form of Myo X, which appears to inhibit neurite extension and axon guidance, provides a potential mechanism for repulsive signaling by neogenin.

X.-J. Zhu, C.-Z. Wang, P.-G. Dai, Y. Xie, N.-N. Song, Y. Liu, Q.-S. Du, L. Mei, Y.-Q. Ding, W.-C. Xiong, Myosin X regulates netrin receptors and functions in axonal path-finding. Nat. Cell Biol. 9, 184-192 (2007). [PubMed]