Expression of SCG10 and stathmin proteins in the rat olfactory system during development and axonal regeneration

The membrane-associated protein SCG10 is expressed specifically by neuronal cells. Recent experiments have suggested that it promotes neurite outgrowt h by increasing microtubule dynamics in growth cones. SCG10 is related to t he ubiquitous but neuron-enriched cytosolic protein stathmin. To better und erstand the role played by SCG10 and stathmin in vivo, we have analyzed the expression and localization of these proteins in both the olfactory epithe lium and the olfactory bulb in developing and adult rats, as well as in adu lt bulbectomized rats. The olfactory epithelium is exceptional in that olfa ctory receptor neurons constantly regenerate and reinnervate the olfactory bulb throughout animal life-span. SCG10 and stathmin expression in the olfa ctory receptor neurons was found to be regulated during embryonic and postn atal development; and to correlate with neuronal maturation. Whereas SCG10 expression was restricted to immature olfactory receptor neurons (GAP-43-po sitive, olfactory marker protein-negative), stathmin was also expressed by the basal cells. In the olfactory bulb of postnatal and adult rats, a moder ate to strong SCG10 immunoreactivity was present in the olfactory nerve lay er, whereas no labeling was detected in the glomerular layer. Olfactory glo meruli also showed no apparent immunoreactivity for several cytoskeletal pr oteins such as tubulin and microtubule-associated proteins. In unilaterally bulbectomized rats, SCG10 and stathmin were seen to be up-regulated in the regenerating olfactory epithelium at postsurgery stages corresponding to o lfactory axon regeneration. Our data strongly suggest that, in vivo, both S CG10 and stathmin may play a role in axonal outgrowth during ontogenesis as well as during axonal regeneration. J. Comp. Neurol. 433:239-254, 2001. (C ) 2001 Wiley-Liss, Inc.