![visual lighting optical arrow visual lighting optical arrow](http://cdn.cnn.com/cnnnext/dam/assets/180504145414-sugiharaplayful-trump-suit.jpg)
(G) Higher magnification of the inset in (F). (F) Branches extended from PocSc but not PgeSc at 52% pd. (F–H) Air sacs extended major branches along the FM. (E) Tracheal lumen (white arrow) can be observed in the PocSc at 47% pd. (D) Two air sacs can be observed, the larger being PocSc and the smaller one being PgeSc (See also Figure 2J). (C) A group of tracheal cell appeared at 42% pd. (B) No tracheal cells were found at 30% pd. (B–H) Tracheal cells were labeled by btl> GFP (green) and trh-lacZ (stained with anti-β-Gal, red). (A) Tracheae labeled by btl> GFP (green) can be found in brain but not in the eye-antennal disc at third instar larva. The process of tracheal development in the Drosophila visual system. Re: retina OL: optic lobe FM: fenestrated membrane PocSc: post-ocular sac PgeSc: post-genal sac DSc: dorsal sac. (L) The tracheae in the optic lobe (OL) were also connected with cervical trachea (CvTra). (K) The DSc extended one major branch to the TNUFM. Two of them are shown in (H) and the third branch is shown in (I, white arrow). The PgeSc extended three major branches to the TNUFM. Four of them are shown in (H) and the fifth branch is shown in (I, black arrow). The PocSc extended five major branches to the TNUFM. (H, I, K, L) The tracheal system (labeled by btl > DsRed in GMR-wIR) in fixed and FocusClear treated half-head samples (H–I, the same sample at different focal planes). (J) The positions of air sacs in the adult head. The pseudocolors indicate the depth from periphery (blue) to center (red). The tracheae were labeled by btl > DsRed in GMR-wIR. (G) 3D reconstruction of tracheae in the whole-mount dissected adult visual system (see also Video S2). (E–F) The tracheal characteristic Taenidium (ring structure, red arrow), and surrounding mitochondria (blue arrow) can be observed. (D) Tracheal lumen can be observed (red boxes, higher magnification in E-F). (D–F) Electron microscopy images of the proximal region of the retina.
![visual lighting optical arrow visual lighting optical arrow](https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fnature22818/MediaObjects/41586_2017_BFnature22818_Fig1_HTML.jpg)
(C) At the distal part of retina, the tracheal cross section appears dot-shaped (white arrow). (B) At the proximal region of the retina, the tracheal cross section appears donut-shaped (white arrow), indicating the tracheal lumen. (A) The tracheal network under the fenestrated membrane (TNUFM, thicker tubes) is connected to the retinal tracheae (thinner tubes). Rhabdomeres and fenestrated membrane (FM) were visualized by autofluorescence (green) from the red pigments of the eye. (A–C) In the optical sections of whole-mount dissected adult retina, the tracheae were labeled by btl>DsRed+ GFP (yellow). Tracheal patterns in adult eye and its relationship with the air sacs in the head. The sections are confocal optical sections. All images in this and the following figures are based on whole-mount fixed tissues. Re: retina OL: optic lobe La: lamina FM: fenestrated membrane (arrowhead). The arrow points to a branching tracheal tube in the retina. One longitudinal optical section of the adult visual system is shown. (D-D”) Visualizing trachea by btl > DsRed (red) in GMR-wIR and by UV-excited autofluorescence (green). The white arrow points to a nucleus expressing trh-lacZ. GFP (green) and trh-lacZ (stained with anti-β-Gal, red).