Promotion and evacuation on standard Young tableaux of rectangle and staircase shape

(Dual-)promotion and (dual-)evacuation are bijections on SYT(\lambda) for any partition \lambda. Let c^r denote the rectangular partition (c,...,c) of height r, and let sc_k (k > 2) denote the staircase partition (k,k-1,...,1). B. Rhoades showed representation-theoretically that promotion on SYT(c^r) exhibits the cyclic sieving phenomenon (CSP). In this paper, we demonstrate a promotion- and evacuation-preserving embedding of SYT(sc_k) into SYT(k^{k+1}). This arose from an attempt to demonstrate the CSP of promotion action on SYT(sc_k).Comment: 14 pages, typos correcte

Peptidergic cell-specific synaptotagmins in Drosophila: Localization to dense-core granules and regulation by the bHLH protein dimmed

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

Ca2+ and synaptotagmin VII–dependent delivery of lysosomal membrane to nascent phagosomes

Synaptotagmin (Syt) VII is a ubiquitously expressed member of the Syt family of Ca2+ sensors. It is present on lysosomes in several cell types, where it regulates Ca2+-dependent exocytosis. Because [Ca2+]i and exocytosis have been associated with phagocytosis, we investigated the phagocytic ability of macrophages from Syt VII−/− mice. Syt VII−/− macrophages phagocytose normally at low particle/cell ratios but show a progressive inhibition in particle uptake under high load conditions. Complementation with Syt VII rescues this phenotype, but only when functional Ca2+-binding sites are retained. Reinforcing a role for Syt VII in Ca2+-dependent phagocytosis, particle uptake in Syt VII−/− macrophages is significantly less dependent on [Ca2+]i. Syt VII is concentrated on peripheral domains of lysosomal compartments, from where it is recruited to nascent phagosomes. Syt VII recruitment is rapidly followed by the delivery of Lamp1 to phagosomes, a process that is inhibited in Syt VII−/− macrophages. Thus, Syt VII regulates the Ca2+-dependent mobilization of lysosomes as a supplemental source of membrane during phagocytosis

Synaptotagmin C2b Ca2+-Binding Loops Impose Distinct Exocytosis Phenotypes

Regulated exocytosis from chromaffin cells in the adrenal medulla plays a critical role in maintaining organismal homeostasis. In the absence of stress, these cells release physiologically relevant substances into the blood stream only in limited quantities, whereas stressful conditions result in a rapid deluge of signaling molecules used, for example, to increase heart rate and pain tolerance. Although the cellular mechanisms governing the switch from low-level to stress-induced secretion are not well understood, recent evidence has implicated the exocytotic Ca2+-sensing protein Synaptotagmin (Syt) in this role. Two isoforms of Syt are expressed in chromaffin cells (Syt-1 and Syt-7), and each is sorted to a different secretory vesicle population. Fusion events mediated by Syt-7 occur under milder stimulation conditions and result in slower release of vesicle cargo through a narrow fusion pore that often reseals (“kiss-and-run” exocytosis). Conversely, Syt-1 events require stronger cellular stimulation (characteristic of a stress response) and typically result in vesicles fully collapsing into the plasma membrane to rapidly release all cargo. Furthermore, Syt-7 remains clustered at fusion sites while Syt-1 rapidly diffuses away. Although the distinct phenotypes of Syt-1 and Syt-7 may explain how chromaffin cells tune their secretory response to deal with intermittent periods of stress, a significant gap in this field is understanding the intermolecular basis for these phenotypic differences. The current study aimed to address this gap by using polarized Total Internal Reflection Fluorescence (pTIRF) microscopy to compare the phenotypes of various Syt chimeras, containing portions of both Syt-1 and Syt-7, with the behavior of the wild-type (WT) proteins. The Ca2+-binding loops of the Syt C2B domain were a prime candidate to target based on this domain’s established role in exocytosis and Ca2+-mediated interactions with other molecules. Chimeras composed of a Syt-1 background with individual C2B loops converted to match Syt-7 showed a mild increase in Syt persistence at fusion sites and slight inhibition of fusion pore expansion when compared to WT Syt-1. These effects were enhanced substantially when all three C2B loops were converted to the Syt-7 genotype, suggesting that the coordinated action of these loops serves as a major determinant of the exocytotic fusion mode

Synaptotagmin‐7 enhances calcium‐sensing of chromaffin cell granules and slows discharge of granule cargos

Synaptotagmin‐7 (Syt‐7) is one of two major calcium sensors for exocytosis in adrenal chromaffin cells, the other being synaptotagmin‐1 (Syt‐1). Despite a broad appreciation for the importance of Syt‐7, questions remain as to its localization, function in mediating discharge of dense core granule cargos, and role in triggering release in response to physiological stimulation. These questions were addressed using two distinct experimental preparations—mouse chromaffin cells lacking endogenous Syt‐7 (KO cells) and a reconstituted system employing cell‐derived granules expressing either Syt‐7 or Syt‐1. First, using immunofluorescence imaging and subcellular fractionation, it is shown that Syt‐7 is widely distributed in organelles, including dense core granules. Total internal reflection fluorescence (TIRF) imaging demonstrates that the kinetics and probability of granule fusion in Syt‐7 KO cells stimulated by a native secretagogue, acetylcholine, are markedly lower than in WT cells. When fusion is observed, fluorescent cargo proteins are discharged more rapidly when only Syt‐1 is available to facilitate release. To determine the extent to which the aforementioned results are attributable purely to Syt‐7, granules expressing only Syt‐7 or Syt‐1 were triggered to fuse on planar supported bilayers bearing plasma membrane SNARE proteins. Here, as in cells, Syt‐7 confers substantially greater calcium sensitivity to granule fusion than Syt‐1 and slows the rate at which cargos are released. Overall, this study demonstrates that by virtue of its high affinity for calcium and effects on fusion pore expansion, Syt‐7 plays a central role in regulating secretory output from adrenal chromaffin cells.Syt‐7 is a high‐affinity calcium sensor expressed on chromaffin cell dense core granules. The purpose of this study was to assess the role of Syt‐7 in regulating the secretory response to cholinergic stimulation. Acetylcholine elicits secretion by elevating cytosolic calcium. The calcium sensitivity of exocytosis in cells lacking Syt‐7 is impaired. Cells that lack Syt‐7 also release peptide hormones at faster rates, implicating a role for Syt‐7 in regulating the exocytotic fusion pore. These data demonstrate that Syt‐7 has an important role in triggering exocytosis in cells and is likely to play a role in controlling hormone output, in situ.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162737/3/jnc14986.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162737/2/jnc14986-sup-0001-Supinfo.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162737/1/jnc14986_am.pd

Cytosolic SYT/SS18 Isoforms Are Actin-Associated Proteins that Function in Matrix-Specific Adhesion

SYT (SYnovial sarcoma Translocated gene or SS18) is widely produced as two isoforms, SYT/L and SYT/S, that are thought to function in the nucleus as transcriptional coactivators. Using isoform-specific antibodies, we detected a sizable pool of SYT isoforms in the cytosol where the proteins were organized into filamentous arrays. Actin and actin-associated proteins co-immunoprecipitated with SYT isoforms, which also co-sedimented and co-localized with the actin cytoskeleton in cultured cells and tissues. The association of SYT with actin bundles was extensive yet stopped short of the distal ends at focal adhesions. Disruption of the actin cytoskeleton also led to a breakdown of the filamentous organization of SYT isoforms in the cytosol. RNAi ablation of SYT/L alone or both isoforms markedly impaired formation of stress fibers and focal adhesions but did not affect formation of cortical actin bundles. Furthermore, ablation of SYT led to markedly impaired adhesion and spreading on fibronectin and laminin-111 but not on collagen types I or IV. These findings indicate that cytoplasmic SYT isoforms interact with actin filaments and function in the ability cells to bind and react to specific extracellular matrices