Epigenetic modifications play key roles in transcriptional regulation. Trimethylation of histone 3 lysine 9 (H3K9me3) is one of the most widely studied histone post-translational modifications, and has been linked to transcriptional repression. In Drosophila melanogaster, Windei is needed for H3K9me3 in female germ line cells. Here, we report the occurrence of a D. melanogaster Windei (Wde) ortholog in the ovary of the hemimetabolous insect Blattella germanica, which we named BgWde. Depletion of BgWde by RNAi reduced H3K9me3 in follicular cells, which triggered changes in transcriptional regulation that led to the prevention of chorion gene expression. In turn, this impaired oviposition (and the formation of the ootheca) and, therefore, prevented reproduction. Windei and H3K9me3 have already been reported in follicular cells of D. melanogaster, but this is the first time that the function of these modifications has been demonstrated in the said cells. This is also the first time that an epigenetic marker is reported as having a key role in choriogenesis.

Support for this research was provided by the Spanish Ministry of Science and Innovation (Grant nos. BFU2011-22404 to MDP and CGL2008-03517/BOS to XB), by the CSIC (Grant no. 2010TW0019, Formosa program) and from FEDER funds to XB. Support from Generalitat de Catalunya (Grant no. 2005 SGR 00053) and LINC-Global is also gratefully acknowledged. AH received a pre-doctoral research grant (JAE-LINCG program) from the CSIC, and The European Social Fund (ESF).