Practice question

Terminal regions acron at anterior and telson at posterior are non-segmented ends of Drosophila body plan specified by terminal maternal effect group. Unlike Bicoid and Nanos localized determinants, Torso receptor tyrosine kinase is uniformly distributed in embryonic membrane with ligand Trunk secreted by follicle cells and activated only at poles by Torso-like. Ligand binding dimerizes Torso, triggering Ras-MAPK cascade via D-Raf, MEK, releasing transcriptional repression by Groucho and Capicua. This permits expression of tailless and huckebein specifically at poles, which pattern acron and telson irrespective of central segmentation programs.