A role for C/EBP[beta] in neuronal differentiation and neuronal regeneration /

Both the differentiation of cortical neurons during development and the regeneration of neurons following peripheral nerve injury are characterized by an increasing expression of axonal proteins such as Talpha1 alpha-tubulin. The mechanisms that regulate the expression of Talpha1 alpha-tubulin and other neuronal genes during differentiation and regeneration are poorly understood. The proximal promoter region of the Talpha1 alpha-tubulin gene contains putative binding sites for the C/EBP family of transcription factors, which is implicated in the regulation of genes in many differentiating cell types or in cells responding to stress. This thesis consists in defining the role of C/EBP family members in the induction of the Talpha1 alpha-tubulin gene in the early differentiation and in the regeneration of neurons. Specifically, the results presented here suggest that C/EBP family members bind to and transactivate the Talpha1 alpha-tubulin minimal promoter and that the Talpha1 alpha-tubulin promoter region that is responsive to C/EBP family members also contains neuronal differentiation and regeneration response elements.Cortical progenitor cell fate involves collaborations between cell-intrinsic factors and extracellular cue-activated signalling pathways. Similarly, the activity of C/EBP family members is regulated by cell-intrinsic factors and by the extrinsically activated Erk 1/2-C/EBP signalling pathway in several differentiating non-neuronal cells. Here we present evidence of an analogous function for C/EBP family members in neurogenesis. The results presented in this thesis show that (1) inhibition of MEK (upstream of Erk 1/2) or inhibition of C/EBP family members blocks cortical progenitor neurogenesis; (2) inhibition of C/EBP family members promotes CNTF-induced astrogenesis; and (3) forced expression of a C/EBPbeta mutant (that is, a mimic of its Erk 1/2-RSK phosphorylated form) enhances the expression of neuron-specific genes such as Talpha1 alpha-tubulin.Neuronal regeneration involves the re-activation of some development-associated genes such as Talpha1 alpha-tubulin and GAP-43. To further define the role of C/EBP family members in the transcription of the Talpha1 alpha-tubulin gene in neurons during regeneration, we crossed transgenic mice that express the beta-galactosidase gene under the control of the Talpha1 alpha-tubulin minimal promoter (Talpha1MP:nLacZ) with mice that carry a null mutation for either C/EBPbeta or C/EBPdelta. The results of facial nerve crush experiments conducted on these hybrid mice show that C/EBPbeta plays a role in the transcriptional activation of the Talpha1 alpha-tubulin minimal promoter following neuronal injury. Injury-induced mRNA expression for either Talpha1 alpha-tubulin or GAP-43 was not noticeably affected by the absence of C/EBPbeta. This suggests that C/EBPbeta-independent mechanisms also play a role in neuronal regeneration