THE DROSOPHILA FAB-7 CHROMOSOMAL ELEMENT CONVEYS EPIGENETIC INHERITANCE DURING MITOSIS AND MEIOSIS

Polycomb group (PcG) and trithorax group (trxG) gene products are resp onsible for the maintenance of repressed and active expression pattern s of many developmentally important regulatory genes including the hom eotic genes. In Drosophila embryos, Polycomb protein and the trxG prot ein GAGA factor colocalize at the Fab-7 DNA element of the bithorax co mplex. In transgenic lines, the Fab-7 element induces extensive silenc ing on a flanking GAL4-driven lacZ reporter and mini-white genes. Howe ver, a short single pulse of GAL4 during embryogenesis is sufficient t o release PcG-dependent silencing from the transgene. Such an activate d state of Fab-7 is mitotically inheritable through development and ca n be transmitted in a GAL4-independent manner to the subsequent genera tions through female meiosis. Thus, Fab-7 is a switchable chromosomal element, which can convey memory of epigenetically determined active a nd repressed chromatin states.