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A cellular memory module conveys epigenetic inheritance of hedgehog expression during Drosophila wing imaginal disc development
Zentrum für Molekulare Biologie Heidelberg (ZMBH), University of
Heidelberg, D-69120 Heidelberg, Germany
In Drosophila, the Trithorax-group (trxG) and Polycomb-group
(PcG) proteins interact with chromosomal elements, termed CellularMemory Modules (CMMs). By modifying chromatin, this ensures astable
heritable maintenance of the transcriptional state of developmentalregulators, like the homeotic genes, that is defined embryonically.We
asked whether such CMMs could also control expression of genesinvolved
in patterning imaginal discs during larval development.Our results
demonstrate that expression of the hedgehog gene,once
activated, is maintained by a CMM. In addition, our experimentsindicate that the switching of such CMMs to an active state duringlarval stages, in contrast to embryonic stages, may require specifictrans-activators. Our results suggest that the patterning of
cellsin particular developmental fields in the imaginal discs doesnot
only rely on external cues from morphogens, but also dependson the
previous history of the cells, as the control by CMMs ensuresa
preformatted gene expression pattern.