title: Peptidergic cell-specific synaptotagmins in Drosophila: localization to dense-core granules and regulation by the bHLH protein DIMMED.
abstract: Bioactive peptides are packaged in large dense-core secretory vesicles, which mediate regulated secretion by exocytosis. In a variety of tissues, the regulated release of neurotransmitters and hormones is dependent on calcium levels and controlled by vesicle-associated synaptotagmin (SYT) proteins. Drosophila express seven SYT isoforms, of which two (SYT-α and SYT-β) were previously found to be enriched in neuroendocrine cells. Here we show that SYT-α and SYT-β tissue expression patterns are similar, though not identical. Furthermore, both display significant overlap with the bHLH transcription factor DIMM, a known neuroendocrine (NE) regulator. RNAi-mediated knockdown indicates that both SYT-α and SYT-β functions are essential in identified NE cells as these manipulations phenocopy loss-of-function states for the indicated peptide hormones. In Drosophila cell culture, both SYT-α and neuropeptide cargo form DIMM-dependent fluorescent puncta that are coassociated by super-resolution microscopy. DIMM is required to maintain SYT-α and SYT-β protein levels in DIMM-expressing cells in vivo. In neurons normally lacking all three proteins (DIMM(-)/SYT-α(-)/SYT-β(-)), DIMM misexpression conferred accumulation of endogenous SYT-α and SYT-β proteins. Furthermore transgenic SYT-α does not appreciably accumulate in nonpeptidergic neurons in vivo but does so if DIMM is comisexpressed. Among Drosophila syt genes, only syt-α and syt-β RNA levels are upregulated by DIMM overexpression. Together, these data suggest that SYT-α and SYT-β are important for NE cell physiology, that one or both are integral membrane components of the large dense-core vesicles, and that they are closely regulated by DIMM at a post-transcriptional level.
authors.affiliation: Department of Anatomy and Neurobiology and.
authors.forename: Dongkook
authors.initials: D
authors.lastname: Park
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Peiyao
authors.initials: P
authors.lastname: Li
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Adish
authors.identifier: http://orcid.org/0000-0002-5491-7709
authors.initials: A
authors.lastname: Dani
authors.affiliation: Department of Anatomy and Neurobiology and taghertp@pcg.wustl.edu.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Taghert
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004330:Drosophila / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism / Q000648:ultrastructure; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D022142:Secretory Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D050857:Synaptotagmins / Q000235:genetics / Q000378:metabolism*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D029721:Drosophila Proteins; D020033:Protein Isoforms; D050857:Synaptotagmins; C491313:dimm protein, Drosophila
keywords: DIMM; Drosophila; LDCV; neuropeptide; super-resolution; synaptotagmin