“…This strategy can be further refined using computational approaches, by which transcription factor binding sites and other cis -acting sequences involved in tissue specificity and promoter strength can be identified from microarrays and genome-wide functional analyses. 222 By assembling different combinations of such cis -regulatory motifs, it has been possible to select short tissue-specific enhancers able to greatly increase tissue-specific gene expression when added upstream of different promoters, as first demonstrated in mice and NHPs to direct coagulation factor IX expression in the liver from AAV9 vectors. 223 The same strategy was also used to enhance specific gene expression in the heart or in skeletal muscles.…”