Figure 9

Model for Ttk69 regulation of lz in Drosophila eye development. Model for the regulation of lz based upon data from this study, Behan and colleagues [39, 41] and Yan and colleagues [33]. In undifferentiated cells, So and Gl initiate the expression of lz (red oval represents Lz protein product). Yan and Ttk69, both transcriptional repressors, are required to down-regulate expression of lz in undifferentiated cells, keeping Lz levels at an appropriate level. Upon activation of the Ras1/MapK signal transduction cascade, the repressive effects of Yan and Ttk69 on lz expression are relieved, thus enabling cell fate specification events in the R7 cell to proceed.