Fig. 1.

The role of Tll in the segmentation gene network in Drosophila melanogaster. (A) Schematic representation of the segmentation gene network. The terminal gap gene tll is regulated by the terminal maternal system, and (together with hkb) provides a feed-forward regulatory input on trunk gap and pair-rule genes. It is not part of any regulatory feedback loops. Circular arrows indicate cross-regulation among groups of genes. (B) Confocal image showing Tll protein expression in a wild-type embryo during the blastoderm stage (time class: t4). Lateral view. Anterior is to the left, dorsal is up. Image source: http://urchin.spbcas.ru/flyex.