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Fig. 8. Regulation of Hox genes by Krüppel in Tribolium. The repressor activity of the anterior giant domain delimits the anterior border of Tc'Kr. Tc'Kr in turn acts as general posterior repressor for Tc'Dfd and Tc'Scr. The precise boundaries of these gnathal Hox genes are defined by pair-rule genes. Therefore, ectopic gnathal Hox gene expression in Tc'Krjaws is interrupted with double-segmental periodicity. Tc'Kr also determines the anterior border of Tc'Ubx through activation, whereas the anterior border of Tc'Antp is probably set by Tc'gt directly.