The gene NR4A2 is a member of the great family of the nuclear receptors which are factors of transcription activated by a ligand, such as hormone steroid, rétinoide or thyroid hormone. However within this great family, a group of factors, NR4A2 of which makes left, does not possess an identified ligand, this is why they are said orphans. The receptor NR4A2, an immediate early gene, induced by different stimuli, is widely expressed in the brain. The description of its expression during the development to the mouse shows that its anatomical distribution goes together with certain dopaminergics neurons. To study its function, mice (NR4A2-/-) were generated. The analysis of these mice showed that the absence of this gene alters the development and the preservation of dopaminergics neurons in substancia nigra and in ventral tegmental area, as well as the expression of several genes markers of the dopaminergic phenotype. These results placed NR4A2, to the rank of the genes of interest in the study of the neuro-degeneration of dopaminergics neurons involved in the Parkinson's disease. Nevertheless, the description of the expression of this factor in fish, shows, that although it is expressed in dopaminergics regions, it is also widely expressed in regions which are not dopaminergic. The analysis of NR4A2 by loss of function in the fish Danio rerio, the subject of this thesis, has allowed bringing to light certain unknown aspects of the functions of this orphan nuclear receptor. So, the gene NR4A2 regulates the expression of an inhibitive gene of CDK and the expression of an inhibitor of neurogenesis. By this way NR4A2 regulates the expression of said proneuraux genes, because expressed in neuron’s progenitors. These proneural genes are known to participate in the cellular specification, in sub-specification and in the differentiation of several neuronal phenotypes. So, the gene NR4A2 leads to the dopaminergic phenotype in Danio rerio, but it also participates in the induction of the neuro-phenotype NPY, the serotoninergic neuro-phenotype and the neuro-phenotype Gabaergique. These new in vivo data make of NR4A2 an important actor of the neurogenesis whose role turns out much wider than what was supposed until now.