Tissue selective transgene expression

An in vivo method for determining phenotype alteration by a plurality of transcribable units in a non-human tissue of interest comprising the steps of:

• (A) administering to a non-human tissue of interest in vivo,
• a DNA expression vector comprising, in 5′ to 3′ orientation, a plurality of recombination units, wherein a single recombination unit comprises at least one transcribable unit and a first and second target site both recognizable by a site-specific recombinase, wherein said non-human tissue of interest expresses a site-specific recombinase,
• (B) harvesting the tissue of interest,
• (C) separating said tissue of interest into individual cells and sorting said individual cells according to phenotype of interest,
• (D) identifying said transcribable unit(s) expressed in each of said sorted individual cells;
• and
• (E) assaying for the altered phenotype that results from expression of the transcriptional unit(s) in said individual cells,
• wherein
• (i) recombination can only occur between two target sites of the same type, said first target site is located at the 5′ start site of said recombination unit and said second target site is located at the 3′ end of said recombination unit, and
• (ii) for all recombination unites comprised within said DNA vector, the orientation of all of said first target sites are the same, and the orientation of all of said second target sites are the same.