Biology subjects

Hasan, G.

Publications and source records attributed to Hasan, G..

8 recordsLinked to original sources

bioRxiv2023

Orai mediated Calcium entry sets the excitability threshold of central dopaminergic neurons by regulation of gene expression

Maturation and fine-tuning of neural circuits frequently requires neuromodulatory signals that set the excitability threshold, neuronal connectivity and synaptic strength. Here we present a mechanistic study of how neuromodulator stimulated intracellular Ca2+ signals, through the store - operated Ca2+ channel Orai, regulate intrinsic neuronal properties by control of developmental gene expression in flight promoting central dopaminergic neurons (fpDANs). The fpDANs receive cholinergic inputs for release of dopamine at a central brain tripartite synapse that sustains flight (Sharma and Hasan, 2020). Cholinergic inputs act on the muscarinic acetylcholine receptor to stimulate intracellular Ca2+ release through the endoplasmic reticulum (ER) localised inositol 1,4,5-trisphosphate receptor followed by ER-store depletion and Orai mediated store-operated Ca2+ entry (SOCE). Analysis of gene expression in fpDANs followed by genetic, cellular and molecular studies identified Orai-mediated Ca2+ entry as a key regulator of excitability in fpDANs during circuit maturation. SOCE activates the transcription factor Trithorax-like (Trl) which in turn drives expression of a set of genes including Set2, that encodes a histone 3 Lysine 36 methyltransferase (H3K36me3). Set2 function establishes a positive feedback loop, essential for receiving neuromodulatory cholinergic inputs and sustaining SOCE. Chromatin modifying activity of Set2 changes the epigenetic status of fpDANs and drives expression of key ion channel and signaling genes that determine fpDAN activity. Loss of activity reduces the axonal arborisation of fpDANS within the MB lobe, and prevents dopamine release required for maintenance of long flight. HighlightsO_LIStore-operated Ca2+ entry (SOCE) through Orai is required in a set of flight-promoting central dopaminergic neurons (fpDANs) during late pupae and early adults to establish their gene expression profile. C_LIO_LISOCE activates a homeobox transcription factor, Trithorax-like and thus regulates expression of histone modifiers Set2 and E(z) to generate a balance between opposing epigenetic signatures of H3K36me3 and H3K27me3 on downstream genes. C_LIO_LISOCE drives a transcriptional feedback loop to ensure expression of key genes required for neuronal function including the muscarinic acetylcholine receptor (mAChR) and the inositol 1,4,5-trisphosphate receptor (itpr). C_LIO_LIThe transcriptional program downstream of SOCE is key to functional maturation of the dopaminergic neurons, enabling their neuronal excitability, axonal arborization and synaptic transmission required for adult flight. C_LI

neuroscience↗

bioRxiv2022

A Drosophila Wolfram Syndrome 1 (WFS1) homologue synergises with the intracellular Ca2+ release channel, IP3R to affect mitochondrial morphology and function

Wolfram syndrome (WFS) is an autosomal recessive neurodegenerative disorder, 90% of which is caused by loss of function of the endoplasmic reticular membrane protein Wolframin or WFS 1. Wolfram syndrome results in Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and Deafness (DIDMOAD) in humans. In mammalian cells WFS1 interacts with the ER-localised intracellular Ca2+ release channel, Inositol Trisphosphate Receptor 1 (IP3R1) required for IP3 mediated Ca2+ release from the endoplasmic reticulum. Here, we tested functional interactions between IP3R and WFS1 mutants in the context of organismal behaviour and neuronal mitochondrial morphology and physiology in a subset of central dopaminergic neurons of Drosophila melanogaster. We show strong genetic interactions between trans-heterozygotes of wfs1 and itpr (IP3R) mutants by measuring flight deficits. Over-expression of wild-type cDNAs of either interacting partner, wfs1+ or itpr+ rescued the flight deficits. Cellular studies demonstrate changes in mitochondrial Ca2+ entry accompanied by enlarged or swollen mitochondria and decreased mitochondrial content in genotypes that are flight defective. In wfs1 mutant as well as wfs1 knockdown conditions a reduction in the number of dopaminergic neurons was observed. Thus, WFS1 interaction with the IP3R is required in flight regulating central dopaminergic neurons of Drosophila, for optimal mitochondrial Ca2+ entry and maintaining mitochondrial morphology. Our study demonstrates that Drosophila can be a good model system to understand the cellular and molecular basis of Wolfram syndrome, its impact on systemic physiology and suggests its use in testing putative pharmaceutical interventions.

genetics↗

bioRxiv2022

A STIM dependent dopamine-insulin axis maintains the larval drive to feed and grow in Drosophila

Appropriate nutritional intake is essential for organismal survival. In holometabolous insects such as Drosophila melanogaster, 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 and growing, 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 activated 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 function of dopamine neurons that modulates developmental changes in larval feeding behaviour and growth. Author summaryThe 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 Drosophila melanogaster, 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 Drosophila melanogaster, 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 modulated mechanism for feeding and growth whose manipulation could be useful for model organism studies related to feeding disorders, obesity and diabetes.

neuroscience↗

bioRxiv2022

Regulation of Store-Operated Ca2+ Entry by IP3 Receptors Independent of Their Ability to Release Ca2+

Loss of endoplasmic reticular (ER) Ca2+ activates store-operated Ca2+ entry (SOCE) by causing the ER localized Ca2+ sensor STIM to unfurl domains that activate Orai channels in the plasma membrane at membrane contact sites (MCS). Here we demonstrate a novel mechanism by which the inositol 1,4,5 trisphosphate receptor (IP3R), an ER-localized IP3-gated Ca2+ channel, regulates neuronal SOCE. In human neurons, SOCE evoked by pharmacological depletion of ER-Ca2+ is attenuated by loss of IP3Rs, and restored by expression of IP3Rs even when they cannot release Ca2+, but only if the IP3Rs can bind IP3. Imaging studies demonstrate that IP3Rs enhance association of STIM1 with Orai1 in neuronal cells with empty stores; this requires an IP3-binding site, but not a pore. Convergent regulation by IP3Rs, may tune neuronal SOCE to respond selectively to receptors that generate IP3.

cell biology↗

bioRxiv2020

IP3/Ca2+ signals regulate larval to pupal transition under nutrient stress through the H3K36 methyltransferase dSET2

Persistent loss of dietary protein usually signals a shutdown of key metabolic pathways. In Drosophila larvae, that have crossed "critical weight" and can pupariate to form viable adults, such a metabolic shut-down would needlessly lead to death. IP3/Ca2+ signals in certain interneurons (vGlutVGN6341) allow Drosophila larvae to pupariate on a protein-deficient diet by partially circumventing this shutdown through upregulation of neuropeptide signaling and the expression of ecdysone synthesis genes. Here we show that IP3/Ca2+ signals in vGlutVGN6341 neurons drive expression of dSET2, a Drosophila Histone 3 Lysine 36 methyltransferase. Further, dSET2 expression is required for larvae to pupariate in the absence of dietary protein. IP3/Ca2+ signal-driven dSET2 expression upregulates key Ca2+ signaling genes through a novel positive feedback loop. Transcriptomic studies coupled with analysis of existing ChIP-seq datasets identified genes from larval and pupal stages, that normally exhibit robust H3K36 trimethyl marks on their gene bodies and concomitantly undergo stronger downregulation by knockdown of either an intracellular Ca2+ release channel the IP3R or dSET2. IP3/Ca2+ signals thus regulate gene expression through dSET2 mediated H3K36 marks on select neuronal genes for the larval to pupal transition.

developmental biology↗

bioRxiv2020

Modulation of flight and feeding behaviours requires presynaptic IP3Rs in dopaminergic neurons

Innate behaviours, though robust and hard wired, rely on modulation of neuronal circuits, for eliciting an appropriate response according to internal states and external cues. Drosophila flight is one such innate behaviour that is modulated by intracellular calcium release through inositol 1,4,5-trisphosphate receptors (IP3Rs). Cellular mechanism(s) by which IP3Rs modulate neuronal function for specific behaviours remain speculative, in vertebrates and invertebrates. To address this, we generated an inducible dominant negative form of the IP3R (IP3RDN). Flies with neuronal expression of IP3RDN exhibit flight deficits. Spatiotemporal expression of IP3RDN helped identify key flight-modulating dopaminergic neurons with axonal projections in the mushroom body. Attenuation of IP3R function in these presynaptic dopaminergic neurons resulted in flies with shortened flight bouts and a disinterest in seeking food, accompanied by reduced excitability and dopamine release upon cholinergic stimulation. Our findings suggest that the same neural circuit modulates the drive for food search and for undertaking longer flight bouts.

systems biology↗

bioRxiv2018

Neuropeptides required for Drosophila development under nutritional stress are regulated by the ER-Ca2+ sensor STIM

SignificanceElevation of cytosolic Ca2+ is required for the release of neuropeptides from specialised secretory neurons called neuroendocrine cells. Release of Ca2+ stored in the ER, which further triggers Ca2+ entry from the extracellular milieu is called Store-operated Ca2+ entry (SOCE). STIM, an ER protein, is a key regulator of SOCE and its contribution to neuroendocrine cell functioning is not well studied. Using Drosophila larval development under nutrient restriction as a paradigm, we identified two SOCE regulated neuropeptides, Corazonin and short Neuropeptide F. Reducing STIM alters the level of these neuropeptides in the fed as well as nutrient restricted condition. This study suggests that STIM-triggered SOCE may regulate the release of neuropeptides whose activity ultimately regulates adaptation to nutritional stress.\n\nAbstractCytosolic Ca2+ levels are tightly regulated by the sequestration of Ca2+ within the endoplasmic reticulum (ER). Loss of ER Ca2+ is sensed by STromal Interacting Molecule (STIM), whose translocation to the plasma membrane triggers Store Operated Ca2+ Entry (SOCE), and a subsequent rise in cytosolic Ca2+. Relatively little is known about SOCEs contribution to neuroendocrine cells; a neuronal sub-type that specializes in the secretion of neuropeptides (NPs) which ultimately regulate animal physiology and behavior. To investigate how SOCE regulates NPs, Drosophila development under nutrient restriction (NR) was used as the biological context. Genetic experiments identified the requirement of two SOCE-regulated NPs-corazonin (Crz) and short neuropeptide F (sNPF) - for the development of NR larvae to pupae and finally, adulthood. Overexpression of SOCE regulators was sufficient to rescue the development of NR larvae with reduced sNPF or Crz levels. To facilitate cellular investigations, a restricted set of neurons that produce sNPF and Crz, and are activated by NR, were identified. Immunohistochemistry on these neurons and mass spectrometric measurements of their projections showed that dSTIM regulates Crz and sNPF levels at steady state and in response to NR, likely by modulating their release. Genetically increasing neuronal output, in the background of reduced dSTIM, robustly rescued development of NR larvae. Because NP action fundamentally underpins how animals adapt to stimuli, regulation of NPs by STIM triggered SOCE is likely to be important. In situations where SOCE is altered, such as neurodegenerative diseases, this regulation may contribute to disease manifestation and progression.

developmental biology↗

bioRxiv2018

FMRFa receptor stimulated Ca2+ signals alter the activity of flight modulating central dopaminergic neurons in Drosophila melanogaster

Neuropeptide signaling influences animal behavior by modulating neuronal activity and thus altering circuit dynamics. Insect flight is a key innate behavior that very likely requires robust neuromodulation. Cellular and molecular components that help modulate flight behavior are therefore of interest and require investigation. In a genetic RNAi screen for G-protein coupled receptors that regulate flight bout durations, we earlier identified several receptors, including the receptor for the neuropeptide FMRFa (FMRFaR). To further investigate modulation of insect flight by FMRFa we generated CRISPR-Cas9 mutants in the gene encoding the Drosophila FMRFaR. The mutants exhibit significant flight deficits with a focus in dopaminergic cells. Expression of a receptor specific RNAi in adult central dopaminergic neurons resulted in progressive loss of sustained flight. Further, genetic and cellular assays demonstrated that FMRFaR stimulates intracellular calcium signaling through the IP3R and helps maintain neuronal excitability in a subset of dopaminergic neurons for positive modulation of flight bout durations.\n\nAuthor summaryNeuropeptides play an important role in modulating neuronal properties such as excitability and synaptic strength and thereby influence innate behavioral outputs. In flying insects, neuromodulation of flight has been primarily attributed to monoamines. In this study, we have used the genetically amenable fruit fly, Drosophila melanogaster to identify a neuropeptide receptor that is required in adults to modulate flight behavior. We show from both knockdown and knockout studies that the neuropeptide receptor, FMRFaR, present on a few central dopaminergic neurons, modulates the duration of flight bouts. Overexpression of putative downstream molecules, the IP3R, an intracellular Ca2+-release channel, and CaMKII, a protein kinase, significantly rescue the flight deficits induced by knockdown of the FMRFaR. Our data support the idea that FMRFaR and CaMKII help maintain optimal membrane excitability of adult dopaminergic neurons required to sustain longer durations of flight bouts. We speculate that the ability to maintain longer flight bouts in natural conditions enhances the individuals capacity to search and reach food sources as well as find sites suitable for egg laying.

genetics↗