A. CRISPR-Cas9 strategy to derive HUVECs with an excision of the LE in the RAB13 3'UTR (∆LE) and parallel generation of wild type (Wt) control cells. The Wt RAB13 exon 8 is represented with its coding sequence in dark and the 3'UTR in clear boxes. The 5' and 3' gRNA-targeted regions are represented with green lines. Arrows: relative positions of the forward (f) and reverse (r) PCR primers used to identify HUVECs with CRISPR-Cas9-mediated excision of the LE. 