Spatiotemporal expression of noncatalytic TrkC NC2 isoform during early and late CNS neurogenesis: a comparative study with TrkC catalytic and p75^NTR receptors

Abstract

The TrkC subfamily of primary high-affinity neurotrophin-3 receptors is composed of catalytic (kinase-containing; TrkC K) and noncatalytic (TrkC NC) isoforms generated by alternative splicing. We previously reported the presence of the mouse noncatalytic TrkC NC2 isoform in regions of neuronal differentiation [Menn, B., Timsit, S., Calothy, G. & Lamballe, F. (1998) J. Comp. Neurol., 401, 47-64]. In order to gain insight into specific roles for TrkC NC2 receptors during CNS neurogenesis, we compared its distribution with that of its catalytic counterparts and the p75NTR receptor in in vivo and in vitro model systems of early and late neuronal differentiation. We found that TrkC NC2 expression coincided with the exit of neuronal progenitors from the cell cycle and was maintained in differentiated cerebellar neurons. We also showed that, whilst TrkC K receptors were expressed both in mitotic and postmitotic cells, TrkC NC2 was present only in differentiating neural stem cell progeny, suggesting its involvement in neuronal and glial cell differentiation. During neuritogenesis of primary neocortical neurons, both TrkC isoforms as well as p75NTR were located in axonal and dendritic processes. However, whilst these various receptors were present in the same neuronal compartments, TrkC NC2 distribution was specifically restricted to distinct areas of extending neurites. Taken together, these findings suggest that spatiotemporal localization of the noncatalytic receptor could account for specific local effects of neurotrophin-3.

The noncatalytic TrkCNC2 receptor is cleaved by metalloproteases upon neurotrophin-3 stimulation

“…Interestingly, these data are in agreement with a study reporting that TrkCNC2 was capable of inducing neuronal differentiation of avian neural crest cells in collaboration with p75 NTR (Hapner et al, 1998). Moreover, in mature neurons, TrkCNC2 distribution was specifically restricted to distinct areas of extending neurites, suggesting its involvement in synaptic plasticity and neuronal survival (Menn et al, 2000).…”

“…In vivo studies showed that trkC NC2 transcripts were abundant in regions of neuronal maturation. In addition, TrkC NC2 expression in neural stem cells coincided with the exit of neural progenitors from the cell cycle, suggesting its involvement in neuronal and glial cell differentiation (Menn et al, 2000). Interestingly, these data are in agreement with a study reporting that TrkCNC2 was capable of inducing neuronal differentiation of avian neural crest cells in collaboration with p75 NTR (Hapner et al, 1998).…”

“…Finally, to rule out the possibility that generation of p20 TrkCNC2 was merely a consequence of ectopic receptor expression in fibroblasts, we investigated its presence in lysates of cortical neurons cultured in NT-3-and serumdeprived medium, and of adult mouse brain, previously shown to express endogenous TrkCNC2 protein (Menn et al, 1998(Menn et al, , 2000. Interestingly, we detected the presence of p20 TrkCNC2 , in addition to that of the mature full-length TrkCNC2 receptor (gp105 TrkCNC2 ), by immunoprecipitation followed by Western blot analysis with anti-NC2 serum ( Figure 5).…”

“…Antibodies used were directed against either the specific NC2 cytoplasmic domain (anti-NC2), the catalytic TK domain (anti-K) or the extracellular domain of the TrkC receptor (anti-Ext). Specificity of these immune sera was assessed in previous studies (Menn et al, 1998(Menn et al, , 2000. Both NC2 and Ext antisera identified two major protein species with apparent molecular masses of 110 and l00 kDa, likely to represent the mature form and the partially glycosylated precursor, respectively ( Figure 1a).…”

“…A total of 250 mg of protein was resolved by 8% SDS-PAGE, and analysed by Western blot using anti-Ext antibodies. Anti-NC2 and anti-EXT antibodies were previously described (Menn et al, 2000). Anti-K serum (Calbiochem) recognizes specifically the TrkC catalytic receptor.…”