We performed the same experiment by transfecting U87 with miR-5096 mimic (30 nM) before culturing them with DiL-C18-labelled HMEC (ratio 1:1) for 12 hours. High levels of miR-5096 were also detected both in U87 and HMEC (Figure 2C, 2D). No increase in miR-5096 expression level in HMEC was observed in non-contact co-cultures with U87 (not shown). To evaluate the contribution of gap junctions to miR-5096 transfer from glioblastoma cells to HMEC, co-culture was made in the presence of carbenoxolone, in order to block the gap junction intercellular communication (GJIC) [11, 20]. Clearly, inhibition of GJIC prevented the miR-5096 increase in HMEC (Figure 2D), i.e.- the miR-5096 expression in HMEC remained very low in the presence of carbenoxolone (0.761±0.4 × 10-4) as compared to cells cultured alone (0.801±0.4 × 10-4, n=3; P>0.5). Because Cx43 is mostly involved in GJIC between HMEC and U87 , we knocked down Cx43 expression in U87 by using specific siRNA (see supplementary Figure S3A). The down regulation of Cx43 in U87 prevented the transfer of miR-5096 to HMEC (see supplementary Figure S3C). It is to note that carbenoxolone also prevented the transfer of miR-145-5p from HMEC to U87; the miR-145 expression levels in U87 were 2.2742±0.43 and 2.21±0.1 × 10-4, respectively in the absence and in the presence of carbenoxolone (means ± SD; P<0.05; n = 3), i.e. a miR-145 level similar to homotypic U87 culture (2.601±0.1 × 10-4, n=3; P>0.5). Thus, the two miRs were exchanged through the same pathway.