miR-shRNA expression options. A) Flow chart for expressing miR-shRNA in different expression platforms. Experimental details of the various steps are provided in methods. B) Comparison of MSCV LTR and beta actin promoters expressing arrestin 2 (Arr2) miR-shRNA or control luciferase (Luc) miR-shRNA in lentivirally infected RAW264.7 macrophages. Constructs used for lentivirus production are detailed in Additional file 3.