Identification and characterization of genes involved in subcellular lumen formation in the Drosophilia larval tracheal system

A common pattern in systems designed to transport liquids and gases, such as the vascular and respiratory systems, is the use of branched tubular structures to create a network that interconnects the entire body. The cellular cues required for generating these complex networks are not well understood. To identify components involved in generating branched tubular networks we are studying the Drosophila melanogaster tracheal (respiratory) system. The Drosophila larval tracheal system is composed of approximately 10,000 interconnected tubes which serve to transport oxygen and other gases throughout the body. The branching and tubulogenesis (the formation of an open space or lumen that extends throughout the length of a branch to make it a tube) seen during Drosophila tracheal system development may parallel similar processes seen in other organisms. The molecular and genetic tools available for Drosophila provide us an excellent opportunity to identify factors required in branching and lumen formation. A forward genetic screen of the X chromosome was conducted to isolate lethal mutations affecting branching and lumen formation in tracheal terminal cells of Drosophila. Tracheal terminal cells are specialized cells that undergo subcellular branching and tubulogenesis, and are responsible for transporting gases and exchanging gases in hypoxic tissues. Thirty-two lines with mutations affecting different aspects of branching and lumen formation were identified. Of these 32 we focused on five iv lines in which tracheal terminal cells undergo essentially normal branching, but are unable to generate a functional lumen. These mutants have been mapped to discrete genetic intervals using a recombination mapping strategy. The mapping has been further refined for two of these five lines by using a combination of single nucleotide polymorphisms (SNP) and P-element recombination frequencies allowing us to identify a small number of candidate genes for each of these mutations. Additionally, for one of these mutants we have identified the causative gene as Zpr1 (Zinc-finger protein 1), an evolutionarily conserved protein characterized by two C4 zinc fingers and two conserved homology domains.