Homeostatic mechanisms for iron storage revealed by genetic manipulations and live imaging of Drosophila ferritin.
Ferritin is a symmetric, 24-subunit iron-storage complex assembled of H and L chains. It is found in bacteria, plants, and animals and in two classes of mutations in the human L-chain gene, resulting in hereditary hyperferritinemia cataract syndrome or in neuroferritinopathy. Here, we examined systemic and cellular ferritin regulation and trafficking in the model organism Drosophila melanogaster. We showed that ferritin H and L transcripts are coexpressed during embryogenesis and that both subunits are essential for embryonic development. Ferritin overexpression impaired the survival of iron-deprived flies. In vivo expression of GFP-tagged holoferritin confirmed that iron-loaded ferritin molecules traffic through the Golgi organelle and are secreted into hemolymph. A constant ratio of ferritin H and L subunits, secured via tight post-transcriptional regulation, is characteristic of the secreted ferritin in flies. Differential cellular expression, conserved post-transcriptional regulation via the iron regulatory element, and distinct subcellular localization of the ferritin subunits prior to the assembly of holoferritin are all important steps mediating iron homeostasis. Our study revealed both conserved features and insect-specific adaptations of ferritin nanocages and provides novel imaging possibilities for their in vivo characterization.
Missirlis
Fanis
F
Neural Cell-Fate Determinants Section, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland 20892, USA. missirlf@mail.nih.gov
Kosmidis
Stylianos
S
Brody
Tom
T
Mavrakis
Manos
M
Holmberg
Sara
S
Odenwald
Ward F
WF
Skoulakis
Efthimios M C
EM
Rouault
Tracey A
TA
D000818:Animals; D030801:Animals, Genetically Modified; D001052:Apoferritins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D005821:Genetic Techniques; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006706:Homeostasis; D007091:Image Processing, Computer-Assisted; D017403:In Situ Hybridization; D007501:Iron / Q000378:metabolism*; D007814:Larva / Q000254:growth & development / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D015347:RNA Probes; D020218:Response Elements / Q000502:physiology; D013347:Subcellular Fractions
D015347:RNA Probes; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D001052:Apoferritins; D007501:Iron