Activation of neurospecific gene expression by antennapedia homeobox peptide

Cholinergic modulation of neurofilament expression and neurite outgrowth in chick sensory neurons

The morphogenetic role of the neurotransmitter acetylcholine was studied in cultures of dorsal root ganglia (DRG) neurons obtained from E12 and E18 chick embryos. With this model we have evaluated neurofilament expression and neurite outgrowth following cholinergic agonist and antagonist treatment. Morphometric analysis undertaken to evaluate fiber outgrowth has indicated that E12 DRG cultures treated with cholinergic agonists, such as muscarine and carbachol, when compared with untreated cultures, have longer fibers and a higher number of fibers per neuron. Concomitant treatment with agonists and the antagonists atropine or mecamylamine counteracts the increase in fiber outgrowth, suggesting that the cholinergic agonist effects were mediated by both muscarinic and nicotinic receptors. The expression of the three neurofilament proteins was also evaluated. Western blot analysis showed that, in E12 DRG cultures, both muscarine and carbachol induce a significant increase in neurofilament protein expression and that this effect is inhibited by cholinergic antagonist treatment. Moreover, Northern blot analysis has demonstrated that the increased expression of 68- and 145-kDa neurofilament proteins is dependent on cholinergic modulation of the neurofilament transcripts. Modulated expression of neurofilament proteins by cholinergic agonists was not evident in E18 DRG cultures, suggesting that, when sensory neurons have completed their differentiation, the cholinergic system might be involved in other functions. In conclusion, our data demonstrate that, during sensory neuron development, acetylcholine modulates neurite outgrowth controlling neurospecific marker expression.

The neuronal microtubule-associated protein 1B is under homeoprotein transcriptional control

To identify genes regulated by homeoprotein transcription factors in postnatal neurons, the DNA-binding domain (homeodomain) of Engrailed homeoprotein was internalized into rat cerebellum neurons. The internalized homeodomain (EnHD) acts as a competitive inhibitor of Engrailed and of several homeoproteins (Mainguy et al., 2000). Analysis by differential display revealed that microtubule-associated protein 1B (MAP1B) mRNA is upregulated by EnHD. This upregulation does not require protein synthesis, suggesting a direct effect of the homeodomain on MAP1B transcription. The promoter region of MAP1B was cut into several subdomains, and each subdomain was tested for its ability to bind Engrailed and EnHD and to associate with Engrailed-containing cerebellum nuclear extracts. In addition, the activity, and regulation by Engrailed, of each subdomain and of the entire promoter were evaluated in vivo by electroporation in the chick embryo neural tube. These experiments demonstrate that MAP1B promoter is regulated by Engrailed in vivo. Moreover, they show that one promoter domain that contains all ATTA homeoprotein cognate binding sites common to the rat and human genes is an essential element of this regulation. It is thus proposed that MAP1B, a cytoskeleton protein involved in neuronal growth and regeneration, is under homeoprotein transcriptional regulation.