(A) A cartoon of the FLIP cassette used to construct the GFP hairpin. GFP represents the first 500 coding base pairs of EGFP. Zeo, zeocin resistance gene; L, Lox; P, the cytomegalovirus promoter in the expression plasmid pcDNA3. HomologousGFPfragmentsarefirstclonedasdirectrepeatsintotheFLIPcassette.Tocreateinvertedrepeatsforhairpinproduction,thesecondrepeatisflipped by using Cre recombinase. When transcribed, the inverted repeat forms a GFP dsRNA with a hairpin loop