Fig. 5. Prolonged Bicoid expression dominantly interferes with head development. Head cuticles of wild-type*, NRE1 and NRE2 transgenic embryos in a bcd⁺ background with maternal genotypes (phase contrast, side views, dorsal towards the top, anterior leftwards). (part I) Wild-type* tridentate mouth hooks (mh) with dorsal (large arrow) and ventral (small arrow) projections. The labrum (lr) and epistomal sclerite (eps) are labral segment markers. bcd NRE1 (part II) and NRE2 (part III) mutant transgenics fail to develop the dorsal mh projection. (Part IV) Wild-type* head with notable marked structures (Jürgens et al., 1986): mh, MxSO, AntSO, lr, dorsal arms (da), dorsal bridge (db) and posterior pharyngeal wall (ppw). Some mutant transgenic embryos with the mh defect fail to complete head involution, resulting in deformations and altered spatial relationships among cuticle structures. NRE1 (part V) and NRE2 (part VI) transgenics with a reduced head skeleton, deformed protruding lr and mh defect. Black arrows: structures residing in a different focal plane. Parts I-III visualize mh abnormality and parts IV-VI reveal head involution defects. Scale bar: 20 µm in parts I-III; 40 µm in parts IV-VI.