Compartmentalizing the embryo: lipids and septate junction mediated barrier function

Abstract

Lipid phosphate phosphatases (LPPs) are a class of enzymes that can dephosphorylate a number of lysophopholipids in vitro. Analysis of knockouts of LPP family members has demonstrated striking but diverse developmental roles for these enzymes. LPP3 is required for mouse vascular development while the Drosophila LPPs Wunen (Wun) and Wunen2 (Wun2) are required during embryogenesis for germ cell migration and survival. In a recent publication we examined if these fly LPPs have further developmental roles and found that Wun is required for proper tracheal formation. In particular we highlight a role for Wun in septate junction mediated barrier function in the tracheal system. In this paper we discuss further the possible mechanisms by which LPPs may influence barrier activity.

Keywords: Drosophila; Serpentine; Vermiform; Wunen; Wunen2; barrier; septate junction; trachea.

Figure 1. 70 kDa dextran can leak into the trachea of cora and wun mutants. 70 kDa dextran was injected into the hemolymph of stage 16 wild type and cora and wun wun2 mutants, and embryos were imaged 10 min after injection. 70 kDa dextran is visible in the trachea of cora and wun wun2 embryos, but not wild type embryos. Arrows indicate the tracheal dorsal trunk.

Figure 2. Pathways that contribute to SJ formation and localization. The proteins required for SJ formation and localization can be divided into four classes (see text). The proteins indicated with the dotted line box are necessary for the interaction and formation of the SJ “core”. The other groups of proteins are not required for SJ core complex formation, but are instead required for proper SJ localization. A failure in SJ complex formation or localization causes Serp and Verm to no longer accumulate in the tracheal lumen, while the 2A12 antigen is unaffected. We hypothesize that Wun acts to produce a lipid product (indicated by a gray circle), which could affect SJs via one or more of the aforementioned pathways.