Figure 4

Expression of tailless ( tll ) during viviparous and oviparous embryogenesis . A-E. tll expression in viviparous embryos. tll mRNA is not detected in germaria or oocytes (stage 1 in A), early or late blastoderm embryos (stage 5 in B, stage 7 in C), or prior to invagination (stage 8 in close-up in D). tll mRNA is first detected after germ band formation in two anterior bilateral spots within cephalic lobes, corresponding to developing brain (stage 10 in C, arrowhead). Domains spread to full extent of cephalic lobes (stage 12 in D, arrowhead) and persist but become more nuanced, reflecting development of eye and central nervous system (stage 18 in E, antennae and limbs indicated by arrows). In all panels, anterior to the left; E dorsal, up. Stage 10 in C, ventral view. Stage 12 in D, lateral view of embryo with anatrepsis, causing inversion of embryonic dorsal-ventral and anterior-posterior axes within egg. Cephalic head lobes (staining) not inverted but displaced towards posterior (right) of egg. Embryo is outlined by white lines. E, lateral view following katatrepsis, returning head lobes to anterior of egg. Extent of head lobe and outlines of leg appendages indicated by black lines. F. Lateral view of tll expression in head lobes (arrowhead) of oviparous embryo still forming abdominal segments (~6 days after egg laying). Note absence of staining (asterisk) at posterior abdomen, which curls under embryo ventrally (bacteriome located dorsally, arrow). Posterior abdomen outlined by black lines; approximate extents of cephalic lobe, gnathos, thorax, and abdomen indicated by vertical black lines. Nuclei stained with DAPI shown in F^′. ab, abdomen; bac, bacteriome; bc, blastocoel; cl, cephalic lobe; g, germarium; gn, gnathos; o, oocyte; th, thorax. Scale bars: A-C, 20 μm; D, 100 μm (inset, 20 μm); E, F, 100 μm. Staging according to [8].