Sensor Stromal Interaction Molecule Research Articles

Role of the microtubule cytoskeleton in the function of the store-operated Ca2+ channel activator STIM1

We examined the role of the microtubule cytoskeleton in the localization and store-operated Ca(2+) entry (SOCE) function of the endoplasmic reticulum (ER) Ca(2+) sensor stromal interaction molecule 1 (STIM1) in HEK 293 cells. STIM1 tagged with an enhanced yellow fluorescent protein (EYFP-STIM1) exhibited a fibrillar localization that colocalized with endogenous alpha-tubulin. Depolymerization of microtubules with nocodazole caused a change from a fibrillar EYFP-STIM1 localization to one that was similar to that of the ER. Treatment of HEK 293 cells with nocodazole had a detrimental impact on SOCE and the associated Ca(2+) release-activated Ca(2+) current (I(CRAC)). This inhibition was significantly reversed in cells overexpressing EYFP-STIM1, implying that the primary inhibitory effect of nocodazole is related to STIM1 function. Surprisingly, nocodazole treatment alone induced significant SOCE and I(CRAC) in cells expressing EYFP-STIM1, and this was accompanied by an increase in EYFP-STIM1 fluorescence near the plasma membrane. We conclude that microtubules play a facilitative role in the SOCE signaling pathway by optimizing the localization of STIM1.

On the Yellow Pigments Found in the Viscera in Cases of Arsenical Poisoning

<h3>Abstract</h3> Appropriate nutritional intake is essential for organismal survival. In holometabolous insects such as <i>Drosophila melanogaster</i>, the quality and quantity of food ingested as larvae determines adult size and fecundity. Here we have identified a subset of dopaminergic neurons (THD’) that maintain the larval motivation to feed. Dopamine release from these neurons requires the ER Ca²⁺ sensor STIM. Larvae with loss of STIM stop feeding, whereas expression of STIM in THD’ neurons rescues feeding, growth and viability of STIM null mutants. Moreover STIM is essential for maintaining excitability and release of dopamine from THD’ neurons. Optogenetic stimulation of THD’ neurons identified connectivity to neuropeptidergic cells, including median neuro secretory cells that secrete insulin-like peptides. Loss of STIM in THD’ cells alters the developmental profile of specific insulin-like peptides including ilp3. Loss of ilp3 partially rescues STIM null mutants and inappropriate expression of ilp3 in larvae affects development and growth. In summary we have identified a novel STIM-dependent dopamine-ILP circuit that regulates developmental changes in larval feeding behaviour. <h3>Author summary</h3> The ability to feed appropriately when hungry is an essential feature for organismal survival and is under complex neuronal control. An array of neurotransmitters and neuropeptides integrate external and internal signalling cues to initiate, maintain and terminate feeding. In adult vertebrates and invertebrates dopamine serves as a reward cue for motor actions, including feeding. Larvae of holometabolous insects, including <i>Drosophila melanogaster</i>, feed and grow constantly followed by gradual cessation of feeding, once sufficient growth is achieved for transition to the next stages of development. Here we identified a subset of larval dopaminergic neurons in <i>Drosophila melanogaster</i>, activity in which maintains continuous feeding in larvae. By analysis of a null mutant we show that these neurons require the Stromal Interaction Molecule (STIM) an ER Ca²⁺ sensor, to maintain excitability. In turn they modulate activity of certain neuropeptidergic cells. Among these are the median neurosecretory cells (MNSc) that synthesize and secrete insulin-like peptides including ilp3. The identified dopaminergic neurons dysregulate the normal pattern of larval ilp3 expression leading to premature cessation of feeding and growth. Overall, our study identified a simple dopamine-insulin feeding circuit whose manipulation could be useful for model organism studies related to feeding disorders, obesity and diabetes.