Fig. 3

L1 retrotransposition rarely occurs in GBM cell lines. a Schematic representing L1 retrotransposition assay. A full-length L1 (L1.3) [61] is located upstream of the antisense oriented blasticidin resistance gene (red boxes). The L1 internal promoter is represented by an arrow on the 5'UTR region. Two L1 open reading frames (ORF1 and ORF2) are indicated by blue and green boxes, respectively. Functional domains of ORF2, endonuclease (EN), reverse transcriptase (RT) and cysteine rich domain (C) are also indicated. The blasticidin resistance gene is interrupted by an intron in the same orientation as the L1. Splice donor (SD) and splice acceptor (SA) sites are indicated. Polyadenylation signals are denoted by grey lollipops. b Schematic representation of retrotransposition assay constructs. JJ L1.3 WT contains an external promoter (cytomegalovirus promoter, CMV) upstream of a full length retrotransposition-competent L1.3 element [61]. Asterisk indicates missense mutation to abolish endonuclease activity (JJ L1.3 D205A), reverse-transcriptase activity (JJ L1.3 D702A) or both (JJ L1.3 D205A D702A). c Results of cell culture-based L1 retrotransposition assay. Each stained colony represents a cell where a retrotransposition event took place allowing the expression of the blasticidin resistance gene