Fig. 2

Tools for transposon-mediated mutagenesis. a Transposase expression can be either ubiquitous (ub. prom.) or directed to a particular cell or tissue type by using Cre-inducible alleles of the transposase enzyme. In the latter case, a loxP-site-flanked transcriptional stop element (gray triangles and STOP sign, respectively) prevents transcription of the gene encoding transposase. Upon Cre-mediated excision of the loxP-STOP-loxP element, the transposase is expressed in Cre-positive cells. b A variety of transposons have been developed for mutagenesis. SB transposons have been developed that carry either a murine stem cell virus (MSCV) promoter (T2/Onc and T2/Onc2) or the chicken β-actin/CMV enhancer (CAG) promoter (T2/Onc3). To facilitate gene activation, transposons carrying these promoters also contain splice donor (SD) elements, and, for gene disruption, splice acceptor (SA) and polyadenylation (pA) elements (bi-pA bi-directional polyadenylation signal). Versatile SB/PB transposons containing terminal repeats recognized by SB and PB transposases (arrowheads) have also been developed and carry either CAG, MSCV or mouse phosphoglycerate kinase 1 (PGK) promoters (ATP1, ATP2 and ATP3 transposons, respectively). c Using combinations of the aforementioned alleles tabulated here, global or spatiotemporal mutagenesis with co-operating mutations can be performed