Proteins interact with chromosomal elements, termed Cellular Memory Modules (CMMs). The switching of such CMMs to an active state during (during larval stages in this experiment) in contrast to embryonic stages, may require specific trans-activators. (Maurange,C├ędric and Renato Paro. Cellular memory module conveys epigenetic inheritance of hedgehog expression during Drosophila wing imaginal disc development. 2002. Abstract.) (http://genesdev.cshlp.org/content/16/20/2672.abstract)