View Program - 63rd Annual Drosophila Research Conference

The Drosophila trachea is a ramifying network of epithelial tubes with a monolayer of epithelial cells surrounding an apical lumen. Following the formation of continuous tubes, the tube maturation process follows. It is a multistep process: (a) apical secretion to form an apical lumen containing chitin-based extracellular matrix, during which tubes expand in both diameter and length, (b) solute clearance to remove solid luminal matrix and liquid in the lumen, and (c) air filling to inflate the entire trachea. These changes occur at the apical side of the tracheal tubes with little or no changes to the basolateral side.
The Osiris (Osi) gene family is located at a locus that exhibits dosage sensitivity (triplo-lethal and haplo-lethal). The protein sequence annotation of Osi proteins identified an endo/lysosomal signal, a transmembrane domain, a domain of unidentified function DUF1676, and an AQXLAY motif, suggesting that these proteins are likely involved in vesicular trafficking. However, the functional analyses of Osi genes are very limited. Only a few studies indicate the potential role of Osi genes in endosome-mediated protein trafficking. For example, RNAi knockdown of Osi 21 suggests its involvement in lysosome-mediated degradation of endocytosed rhodopsin in Drosophila eye. In addition, Osi23 is essential for the formation of nanopores lining the olfactory sensillum in Drosophila, potentially through endo/lysosome-mediated trafficking. However, the role of Osi genes in Drosophila trachea is still unknown.
Previously we identified several Osi genes with obvious expression in the Drosophila trachea from stage 14 until the end of embryogenesis. In addition, expressing HA-tagged Osi proteins in trachea revealed their localization in vesicle-like structures, suggesting their potential roles in vesicular trafficking. Immunohistochemistry using Osi specific antibodies further confirmed that the endogenous Osi proteins are localized at various endosomes in tracheal cells.
The potential functional redundancy of Osi genes prompted us to generate Osi single, double, and triple loss‐of‐function mutants using CRISPR-cas9. No obvious phenotypes were observed in single mutants. However double and triple mutants showed strong defects in trachea tube maturation. Genetic interaction studies suggest that Osi genes are required for trachea tube maturation through endosome-mediated protein trafficking.

The Osiris family genes regulate endocytic trafficking during Drosophila tracheal maturation