138 Oral - Patterning and Morphogenesis I
Saturday April 09, 8:30 AM - 8:45 AM

Authors:
Srihitha Akula; Rajprasad Loganathan; Tony Zou ; Rika Maruyama; Deborah Andrew

Affiliation: Johns Hopkins University

Keywords:
u. ectodermal derivatives; e. intracellular transport

Malvolio (Mvl) is a member of the SLC11 family of metal ion transporters, and is the Drosophila ortholog of the mammalian natural resistance-associated macrophage proteins (NRAMPs). The family members (NRAMP1 and NRAMP2) function as general metal ion transporters that use proton motive force to transport Fe²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Ni²⁺, and Co²⁺. The key known roles for NRAMPs are in maintaining ion homeostasis essential to support the antimicrobial activities of phagocytic cells. Our interest in Mvl stems from its high-level Fkh-dependent expression in the embryonic salivary gland (SG), an ideal model system for studying tissue morphogenesis and functional specialization. To begin to uncover the role of Mvl in the SG and in other tissues, we generated a null allele of Mvl (Mvl^exc1), transgenic fly lines for expressing both GFP-tagged and untagged Mvl (UAS-Mvl, UAS-Mvl-GFP), as well as Mvl-specific polyclonal antisera. Our initial characterization of Mvl loss-of-function revealed that although zygotic loss of Mvl does not affect viability, development is delayed, with Mvl^exc1/Df(Mvl) adults eclosing 48 – 72 hours after their balancer-containing siblings. To determine if loss of Mvl affects iron accumulation and/or storage, we examined Mvl^exc1 homozygous larvae and found that the Iron-storing epithelial cells of the anterior midgut lose their Ferritin enrichment, whereas the brain Ferritin levels were unaffected (based on Ferritin-GFP signal intensity). Whereas zygotic loss of Mvl had only mild effects on SG morphology and larval cuticles, the combined maternal and zygotic loss of Mvl resulted in earlier, conspicuous defects in SG morphology as well as severe defects in the larval cuticle, with a near complete loss of ventral denticles and dorsal hairs. Mvl homozygotes also featured a loose assemblage of an unidentified CrebA+ population of cells in the anterior region of the embryo. The examination of junctional proteins in Mvl null embryos revealed that levels and localization of the adherens junction protein E-cadherin and polarity marker Bazooka were comparable in Mvl and wild-type SGs, whereas the levels of the apical polarity determinant Crumbs were notably reduced. To learn where Mvl localizes in SG cells and is likely to function, we co-stained embryos with Mvl and several organelle-specific markers. These experiments revealed Mvl localization to Golgi and to both early and late endosomes. Based on these findings, we hypothesize that Mvl may have a role in the trafficking of either newly synthesized or recycled Crb to the sub-apical domain.