The GDNF family ligands signal through a receptor complex composed of a ligand binding subunit, GFRalpha, and a signaling subunit, the RET tyrosine kinase. GFRalphas are expressed not only in RET-expressing cells, but also in cells lacking RET. A body of evidence suggests that RET-independent GFRalphas are important for (1) modulation of RET signaling in a non-cell-autonomous fashion (trans-signaling) and (2) regulation of NCAM function. To address the physiological significance of these roles, we generated mice specifically lacking RET-independent GFRalpha1. These mice exhibited no deficits in regions where trans-signaling has been implicated in vitro, including enteric neurons, motor neurons, kidney, and regenerating nerves. Furthermore, no abnormalities were found in the olfactory bulb, which requires proper NCAM function for its formation and is putatively a site of GDNF-GFRalpha-NCAM signaling. Thus RET-independent GFRalpha1 is dispensable for organogenesis and nerve regeneration in vivo, indicating that trans-signaling and GFRalpha-dependent NCAM signaling play a minor role physiologically.
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