Glial cell line-derived neurtftrophic factor (GDNF) inducible genes and neuronal differentiation

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Glial cell line-derived neurotrophic factor (GDNF) family ligands promote the growth and survival of several population of CMS and PNS neuron via activation of the RET tyrosine kinase. We searched for immediate-early GDNF responsive genes by mRNA differential display technique using TGW neuroblastoma cells and have isolated fourteen GDNF inducible genes including c-fos, CREB and CREM. We focused on two novel genes. One novel gene was induced in the fast kinetics manner like c-fos and its protein sequence deduced from CDNA ORF contains zinc finger repeat in the C-terminal moiety and KRAB domain, BTB/POZ domain in N-terminal, respectively. In northern blot of human multiple tissues, its expression was confirmed in adult kidney as well as skeletal muscle and heart. Interestingly, immunohistochemical staining of mouse embryo showed that ureteric bud epithelia were stained similarly to RET expression but not in adult kidney. We are now evaluating its function using antisense oligonucleotide in the organ culture of the mouse embryonic kidneys. These results suggest that this novel zinc finger protein may play a role in nephrogenesis under Ret/GDNF system in addition to neuronal cells. We also focused on the other unknown gene. Molecular cloning of the full length CDNA of this gene revealed that it was the human homologue which counterpart of budding yeast had an important role in the many cellular process including miosis, RNA metabolism and telomere function. Northern and western blot showed that this gene was also highly induced in the late-phase in the GDNF stimulation. Immunohistochemical staining showed that this gene was expressed in extending neurite in neuroblastoma cells and in neuronal tissues of adult mice and mouse embryo in the later term of embryogenesis. We also found its co-localization with tubulin, suggesting its important role in neurite outgrowth through the mechanism like tubulin stabilization.