Fig. 7.

Model for regulation of SG formation. Scr, Exd and Hth regulate SG formation through the activation of a set of transcription factors expressed early and continuously in this tissue: Sage, Fkh and CrebA. Sage and Fkh activate the expression of genes encoding SG-specific secreted cargo proteins, transmembrane proteins and the enzymes that modify proteins that travel through the secretory pathway. Sage and Fkh also activate transcription of sens, which in turn boosts the expression levels of many Sage-Fkh targets. CrebA upregulates expression of the protein components of the secretory machinery to increase overall secretory capacity and contributes, directly or indirectly, to increased expression of many genes encoding SG cargo proteins. Additional uncharacterized Scr-Exd-Hth-dependent transcription factor(s) are proposed to also be required to maintain SG fate and to regulate the many known SG genes whose expression is unaffected by loss of fkh (Maruyama et al., 2011).