Biology subjects

Sehgal, A.

Publications and source records attributed to Sehgal, A..

43 records · Page 3Linked to original sources

bioRxiv2020

Drosophila clock cells use multiple mechanisms to transmit time-of-day signals in the brain

Regulation of circadian behavior and physiology by the Drosophila brain clock requires communication from central clock neurons to downstream output regions, but the mechanism by which clock cells regulate downstream targets is not known. We show here that the pars intercerebralis (PI), previously identified as a target of the morning cells in the clock network, also receives input from evening cells. We determined that morning and evening clock neurons have time of day dependent connectivity to the PI, which is regulated by specific peptides as well as by fast neurotransmitters. Interestingly, PI cells that secrete the peptide DH44, and control rest:activity rhythms, are inhibited by clock inputs while insulin-producing cells are activated, indicating that the same clock cells can use different mechanisms to drive cycling in output neurons. Inputs of morning cells to the DILP2+ neurons are relevant for the circadian rhythm of feeding, reinforcing the role of the PI as a circadian relay that controls multiple behavioral outputs. Our findings provide mechanisms by which clock neurons signal to non-clock cells to drive rhythms of behavior. Significance StatementDespite our growing understanding of how the fly clock network maintains free-running rhythms of behavior and physiology, little is known about how information is communicated from the clock network to the rest of the brain to regulate behavior. We identify glutamate and acetylcholine as key neurotransmitters signaling from clock neurons to the pars interecerebralis (PI), a clock output region regulating circadian rhythms of sleep and metabolism. We report a novel link between Drosophila evening clock neurons and the PI, and find that the effect of clock neurons on output neuron physiology varies, suggesting that the same clock cells use multiple mechanisms simultaneously to drive cycling in output neurons.

neuroscience↗

bioRxiv2020

Stable colony stimulating factor 1 fusion protein treatment increases HSC pool and enhances their mobilisation in mice.

Prior chemotherapy and/or underlying morbidity commonly leads to poor mobilisation of hematopoietic stem cells (HSC) for transplantation in cancer patients. Increasing the number of available HSC prior to mobilisation is a potential strategy to overcome this deficiency. Resident bone marrow (BM) macrophages are essential for maintenance of niches that support HSC and enable engraftment in transplant recipients. Here we examined potential of donor treatment with colony stimulating factor-1 (CSF1) to modify the BM niche and expand the potential HSC pool for autologous transplantation. We administrated CSF1 Fc fusion protein (CSF1-Fc) to naive C57Bl/6 mice and assessed the impacts on HSC number and function and overall haematopoiesis. Outcomes were assessed by in situ imaging and ex vivo flow cytometry with functional validation by colony formation and competitive transplantation assay. CSF1-Fc treatment caused a transient expansion of monocyte-macrophage cells within BM and spleen at the expense of BM B lymphopoiesis and hematopoietic stem and progenitor cell (HSPC) homeostasis. During the recovery phase after cessation of CSF1-Fc treatment, normalisation of haematopoiesis was accompanied by an increase in the total available HSPC pool. In the spleen, increased HSC was associated with expression of the BM niche marker CD169 in red pulp macrophages. Pre-treatment with CSF1-Fc increased the number and reconstitution potential of HSPC in blood following a HSC mobilising regimen of granulocyte colony stimulating factor (G-CSF) treatment. These results indicate that CSF1-Fc conditioning could represent a therapeutic strategy to overcome poor HSC mobilisation and subsequently improve autologous or heterologous HSC transplantation outcomes. Key points1) Recovery from Fc-modified colony stimulating factor-1 (CSF1-Fc) treatment was accompanied by an increase in total haematopoietic stem cells. 2) Pre-conditioning with CSF1-Fc increased the reconstitution potential of blood after haematopoietic stem cell mobilisation.

cell biology↗

bioRxiv2020

Nest records, Nest Site selection of Gyps bengalensis White-rumped Vulture and the role of Feeding Station in Kangra, Himachal Pradesh

Active nests of Gyps bengalensis White-rumped Vulture depends on elevation and aspects for nest site selection, while feeding station plays a significant role for determining the position of the nesting sites.This study attempted to record nest count for the breeding period 2018, identify key variables for the nest site selection and understand the role of feeding station in the nest site selection. Nest counts were conducted during the breeding period, each nest was categorized into active and inactive nest based on assesment of different components. Simultaneously, different variables (tree height, tree species, elevation and aspect) were recorded for each nest. Aerial distance was used to determine the role of feeding station for selecting the nesting sites. From the 24 nesting sites, 352 active nests were recorded, and a significant Pearsons correlation for elevation and aspect were drawn. We found, vulture prefer single tree species for nesting. We also found that, 71% (n = 17) nesting sites located within radial distance of 20 km of the feeding station. High congregration of active nests within short radial distance from feeding station, signify the positive impact of management of feeding station by the wildlife wing of Forest department since 2008, for the ex-situ conservation of critically endangered Gyps bengalensis White-rumped Vulture

ecology↗

bioRxiv2020

Fecal microbiota transplantation efficacy for Clostridium difficile infection: A trans-kingdom battle between donor and recipient gut microbiomes

Fundamental restoration ecology and community ecology theories can help us better understand the underlying mechanisms of fecal microbiota transplantation (FMT) and to better design future microbial therapeutics for recurrent Clostridium difficile infections (rCDI) and other dysbiosis-related conditions. In a single cohort study, stool samples were collected from donors and rCDI patients one week prior to FMT (pre-FMT) as well as from patients one week following FMT (post-FMT). Using metagenomic sequencing and machine learning methods, our results suggested that the FMT outcome is not only dependent on the ecological structure of the recipients, but also the interactions between the donor and recipient microbiomes, both at the taxonomical and functional levels. Importantly, we observed that the presence of specific bacteria in donors (Clostridiodes spp., Desulfovibrio spp., Odoribacter spp. and Oscillibacter spp.) and the absence of specific fungi (Yarrowia spp.) and bacteria (Wigglesworthia spp.) in recipients prior to FMT could accurately predict FMT success. Our results also suggested a series of interlocked mechanisms for FMT success, including the repair of the disturbed gut microbial ecosystem by transient colonization of nexus species followed by secondary succession of bile acid metabolizers, sporulators, and short chain fatty acid producers. Therefore, a better understanding of such mechanisms can be fundamental key elements to develop adaptive, personalized microbial-based strategies for the restoration of the gut ecosystem. ImportanceThere have been a number of studies focusing on understanding the underlying mechanisms in FMT treatment, which can accordingly be used for the optimization of future treatments. However, the current scientific lens has mainly had a uni-kingdom major focus on bacteria, leading to the proposition of the existence of FMT "super-donors". On the contrary, our preliminary study here suggests that FMT is not necessarily a one stool fits all approach and that donor-recipient cross-kingdom microbiota interactions, along with their short-term fluctuations in the gut, bring profound implications in FMT success. The results also conceptualize a series of interlocked mechanisms for FMT success, including first repairing the disturbed gut microbial ecosystem by transient species, followed by secondary succession of indigenous or exogenous bile acid metabolizers, sporulators, and short chain fatty acid producers.

microbiology↗

bioRxiv2020

A Circuit Mechanism Underlying Suppression of Circadian Signals by Homeostatic Sleep Drive

Sleep is controlled by homeostatic mechanisms, which drive sleep after wakefulness, and a circadian clock, which confers the 24-hour rhythm of sleep. These processes interact with each other to control the timing of sleep in a daily cycle as well as following sleep deprivation. However, the mechanisms by which they interact are poorly understood. We show here that hugin+ neurons, previously identified as neurons that function downstream of the clock to regulate rhythms of locomotor activity, are also targets of the sleep homeostat. Sleep deprivation decreases activity of hugin+ neurons, likely to suppress circadian-driven activity during recovery sleep, and manipulations of hugin+ neurons affect sleep increases generated by activation of the homeostatic sleep locus, the dorsal fanshaped body (dFB). Also, mutations in peptides produced by the hugin+ locus increase recovery sleep following deprivation. Trans-synaptic mapping reveals that hugin+ neurons feed-back onto central clock neurons, which also show decreased activity upon sleep loss, in a Hugin-peptide dependent fashion. We propose that hugin+ neurons integrate circadian and sleep signals to modulate circadian circuitry and regulate the timing of sleep.

neuroscience↗

bioRxiv2019

AANAT1 functions in astrocytes to regulate sleep homeostasis.

Characteristic features of sleep are conserved among species [1], and from humans to insects sleep is influenced by neural circuits involving monoamines such as serotonin and dopamine [2]. Glial cells have been increasingly implicated in mechanisms of baseline and homeostatic sleep regulation in mammals and flies [3-11], but it remains unknown whether and how glia might influence monoaminergic control of sleep. Sleep is regulated by circadian rhythms and a homeostatic drive to compensate for prolonged wakefulness, and growing evidence suggests that neural mechanisms controlling homeostatic sleep can be discriminated from those controlling baseline sleep [12-15]. In Drosophila, mutants of arylalkylamine N-acetyltransferase 1 (AANAT1lo) have normal baseline amounts of sleep and motor activity, but increased rebound sleep following deprivation [16]. AANAT1 can acetylate and inactivate monoamines in vitro [17], but the role of AANAT1 in vivo remains poorly understood. We find AANAT1 to be expressed in astrocytes and subsets of neurons in the adult Drosophila brain, with levels in astrocytes declining markedly overnight. In sleep-deprived AANAT1 mutant flies, heightened rebound sleep is accompanied by increased serotonin and dopamine levels in the brain. In neurons, AANAT1 functions to limit the quantity and consolidation of nighttime sleep, but in astrocytes AANAT1 constrains the amount of rebound sleep that flies take in response to sleep deprivation. These findings distinguish sleep-control functions of AANAT1 in neurons and astrocytes, and identify a critical role for astrocytes in the regulation of monoamine bioavailability and calibration of the response to sleep need.\n\nHighlightsO_LIThe monoamine catabolic enzyme arylalkylamine N-acetyltransferase 1 (AANAT1) is expressed by astrocytes and subsets of serotonergic, glutamatergic, GABAergic and cholinergic neurons in the adult brain of Drosophila.\nC_LIO_LIAANAT1 limits accumulation of serotonin and dopamine in the brain upon sleep deprivation.\nC_LIO_LILoss of AANAT1 from astrocytes, but not from neurons, causes flies to increase their daytime rebound sleep in response to overnight sleep deprivation.\nC_LI

neuroscience↗

bioRxiv2017

A circadian clock in the blood-brain barrier regulates xenobiotic efflux from the brain

HighlightsO_LIThe Drosophila BBB displays a circadian rhythm of permeability\nC_LIO_LICyclic efflux driven by a clock in the BBB underlies the permeability rhythm\nC_LIO_LICircadian control is non-cell-autonomous via gap junction regulation of [Mg2+]i\nC_LIO_LIAn anti-seizure drug is more effective when administered at night\nC_LI\n\nSummaryEndogenous circadian rhythms are thought to modulate responses to external factors, but mechanisms that confer time-of-day differences in organismal responses to environmental insults / therapeutic treatments are poorly understood. Using a xenobiotic, we find that permeability of the Drosophila \"blood\"-brain barrier (BBB) is higher at night. The permeability rhythm is driven by circadian regulation of efflux and depends upon a molecular clock in the perineurial glia of the BBB, although efflux transporters are restricted to subperineurial glia (SPG). We show that transmission of circadian signals across the layers requires gap junctions, which are expressed cyclically. Specifically, during nighttime gap junctions reduce intracellular magnesium ([Mg2+]i), a positive regulator of efflux, in SPG. Consistent with lower nighttime efflux, nighttime administration of the anti-epileptic phenytoin is more effective at treating a Drosophila seizure model. These findings identify a novel mechanism of circadian regulation and have therapeutic implications for drugs targeted to the central nervous system.

neuroscience↗