The invention concerns novel compositions and methods for controlling nucleic acid expression in cells. More particularly, it concerns any nucleic acid characterised in that it comprises: a) a first region comprising a nucleic acid coding for a tetracycline (tTA)-dependent transactivator under the control of a moderate promoter; and b) a second region comprising a nucleic acid of interest under the control of tTA sensitive promoter. The invention is more particularly useful for controlling the expression of nucleic acids in the nerve cells, in vitro as well as in vivo, for example the human tyrosine hydrocyclosis.