The silencing mechanism targeting ZAM and Idefix is active in somatic tissues throughout fly development.

<p>A) In an S/S genetic background, the pGFP-IdU sensor transgene driven by 24B-Gal4 is not expressed in embryos, larvae, or adults (top, middle and bottom panels, respectively). Only a very faint level of fluorescence, corresponding to the background expression of GFP, is detected. B) In a U/U genetic background, the GFP-IdU transgene silencing is released and GFP fluorescence is clearly observed in the three stages analyzed. The fluorescence pattern recapitulates the expression of the HOW gene in muscle and tendon cells, as expected for the 24B-Gal4 driver <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001526#pone.0001526-Brand1" target="_blank">[22]</a>. C) In an S/S genetic background, the pGFP-IdUAS sensor transgene carrying the 5′UTR of <i>Idefix</i> in the opposite orientation is not subjected to the silencing exerted on the <i>Idefix</i> sequences. pGFP-IdUAS is correctly expressed and GFP is detected in embryos, larvae, and adult flies.