Method of regulating gene expression

A method of inhibiting expression of a target gene comprising introducing into an isolated human or non-human animal cell a DNA construct comprising a constitutive or inducible promoter operably linked to a nucleic acid comprising a sequence encoding an artificial micro RNA (miRNA) precursor, wherein said artificial miRNA precursor is a naturally occurring miRNA precursor a portion of the stem of the stem loop structure of said naturally occurring miRNA precursor being substituted by an exogenous sequence complementary to a portion of an RNA transcript of said gene,

• wherein, following introduction of said construct into said cell:
• i) said nucleic acid is transcribed so that a transcript comprising said artificial miRNA precursor is produced,
• ii) said transcript resulting from step (i) is processed so that said artificial miRNA precursor is excised therefrom,
• iii) said artificial miRNA precursor resulting from step (ii) is processed so that a mature miRNA about 21 or 22 nucleotides in length is excised from said artificial miRNA precursor, and
• iv) inhibition of expression of said gene is effected.