The process of tracheal development in the <i>Drosophila</i> visual system.

<p>(A) Tracheae labeled by <i>btl</i>><i>GFP</i> (green) can be found in brain but not in the eye-antennal disc at third instar larva. (B–H) Tracheal cells were labeled by <i>btl</i>><i>GFP</i> (green) and <i>trh-lacZ</i> (stained with anti-β-Gal, red). (B) No tracheal cells were found at 30% pd. (C) A group of tracheal cell appeared at 42% pd. (D–E) Air sacs can be found at 47% pd. (D) Two air sacs can be observed, the larger being PocSc and the smaller one being PgeSc (See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073878#pone-0073878-g002" target="_blank">Figure 2J</a>). (E) Tracheal lumen (white arrow) can be observed in the PocSc at 47% pd. (F–H) Air sacs extended major branches along the FM. (F) Branches extended from PocSc but not PgeSc at 52% pd. (G) Higher magnification of the inset in (F). (H) Major branches extended from PocSc following the posterior-to-anterior direction at 52% pd. Bifurcating branches can be observed (white arrow). (I–J) The tracheal pattern at later pupal stages were labeled by <i>btl > DsRed</i> (white) in <i>GMR-wIR</i> in order to decrease the autofluorescence from the red pigments of eye. (I) Ingrowth of fine tracheal branches to retina at 60% pd. (J) Retinal tracheae continue to extend in length following the thickening retina at 72% pd in a proximal-to-distal direction. (K) Schematic representation of the process of tracheal development in the visual system. TNUFM: the tracheal network under the fenestrated membrane. Re: retina; OL: optic lobe; PocSc: post-ocular sac; PgeSc: post-genal sac.