grim promotes programmed cell death of Drosophila microchaete glial cells

Investigating SARS-CoV-2 virus-host interactions and mRNA expression: Insights using three models of D. melanogaster

Responsible for COVID-19, SARS-CoV-2 is a coronavirus in which contagious variants continue to appear. Therefore, some population groups have demonstrated greater susceptibility to contagion and disease progression. For these reasons, several researchers have been studying the SARS-CoV-2/human interactome to understand the pathophysiology of COVID-19 and develop new pharmacological strategies. D. melanogaster is a versatile animal model with approximately 90 % human protein orthology related to SARS-CoV-2/human interactome and is widely used in metabolic studies. In this context, our work assessed the potential interaction between human proteins (ZNF10, NUP88, BCL2L1, UBC9, and RBX1) and their orthologous proteins in D. melanogaster (gl, Nup88, Buffy, ubc9, and Rbx1a) with proteins from SARS-CoV-2 (nsp3, nsp9, E, ORF7a, N, and ORF10) using computational approaches. Our results demonstrated that all the proteins have the potential to interact, and we compared the binding sites between humans and fruit flies. The stability and consistency in the structure of the gl_nsp3 complex, specifically, could be crucial for its specific biological functions. Lastly, to enhance the understanding of the influence of host factors on coronavirus infection, we also analyse the mRNA expression of the five genes (mbo, gl, lwr, Buffy, and Roc1a) responsible for encoding the fruit fly proteins. Briefly, we demonstrated that those genes were differentially regulated according to diets, sex, and age. Two groups showed higher positive gene regulation than others: females in the HSD group and males in the aging group, which could imply a higher virus-host susceptibility. Overall, while preliminary, our work contributes to the understanding of host defense mechanisms and potentially identifies candidate proteins and genes for in vivo viral studies against SARS-CoV-2.

Mitochondrial dysfunctions elicited by solid waste leachates provide insights into mechanisms of leachates induced cell death and pathophysiological disorders

Emissions (mainly leachates and landfill gases) from solid waste facilities are laden with mixtures of dangerous xenobiotics implicated with significant increase in various pathophysiological disorders including cancer, and eventual mortality of exposed wildlife and humans. However, the molecular mechanisms of solid waste leachates induce pathophysiological disorders and cell death are still largely unknown. Although, evolving evidence implicated generation of reactive oxygen species and oxidative stress as the possible mechanism. Recent scientific reports are linking reactive oxygen species and mitochondrial dysfunctions as the player mechanism in pathophysiological disorder and apoptosis induced by xenobiotics in solid waste leachates. This systematic review presents an explicit discussion of recent scientific findings on the structural and functional alterations in mitochondria induced by solid waste leachates as the molecular mechanisms plausibly responsible for the pathophysiological disorders, cancer and cell death reported in landfill toxicology and epidemiological studies. This review aims to increase scientific understanding on solid waste leachate induced mitochondria dysfunctions as the key player in molecular mechanisms of solid waste induced toxicity. The findings in this review were mainly from using primary cells, cell lines, Drosophila and fish. Whether the findings will similarly be observed in mammalian test systems in vivo and particularly in exposed humans, remained to be investigated. Improvement in technological advancements, enforcement of legislation and regulations, and creation of sophisticated health surveillance against exposure to solid waste leachates, will expectedly mitigate human exposure to solid waste emissions and contamination of the environment.

Programmed cell death reshapes the central nervous system during metamorphosis in insects

Metamorphosis is fascinating and dramatic stage of postembryonic development in insects [1]. The most prominent metamorphic changes seen in holometabolous insects involve destruction of most larval structures and concomitant generation of adult ones. Such diverse cellular events are orchestrated by ecdysone. The central nervous system (CNS) is also extensively remodeled to process new sensory inputs; to coordinate new types of locomotion; and to perform higher-order decision making [2]. Programmed cell death (PCD) is an integral part of the metamorphic development. It eliminates obsolete larval tissues and extra cells that are generated from the morphogenesis of adult tissues. In the CNS, PCD of selected neurons and glial cells as well as reshaping of persistent larval cells are essential for establishing the adult CNS. In this review, we summarize the ecdysone signaling, and then molecular and cellular events associated with PCD primarily in the metamorphosing CNS of Drosophila melanogaster.

Salivary epigenetic biomarkers as predictors of emerging childhood obesity

BACKGROUND

Epigenetics could facilitate greater understanding of disparities in the emergence of childhood obesity. While blood is a common tissue used in human epigenetic studies, saliva is a promising tissue. Our prior findings in non-obese preschool-aged Hispanic children identified 17 CpG dinucleotides for which differential methylation in saliva at baseline was associated with maternal obesity status. The current study investigated to what extent baseline DNA methylation in salivary samples in these 3-5-year-old Hispanic children predicted the incidence of childhood obesity in a 3-year prospective cohort.

METHODS

We examined a subsample (n = 92) of Growing Right Onto Wellness (GROW) trial participants who were randomly selected at baseline, prior to randomization, based on maternal phenotype (obese or non-obese). Baseline saliva samples were collected using the Oragene DNA saliva kit. Objective data were collected on child height and weight at baseline and 36 months later. Methylation arrays were processed using standard protocol. Associations between child obesity at 36 months and baseline salivary methylation at the previously identified 17 CpG dinucleotides were evaluated using multivariable logistic regression models.

RESULTS

Among the n = 75 children eligible for analysis, baseline methylation of Cg1307483 (NRF1) was significantly associated with emerging childhood obesity at 36-month follow-up (OR = 2.98, p = 0.04), after adjusting for child age, gender, child baseline BMI-Z, and adult baseline BMI. This translates to a model-estimated 48% chance of child obesity at 36-month follow-up for a child at the 75th percentile of NRF1 baseline methylation versus only a 30% chance of obesity for a similar child at the 25th percentile. Consistent with other studies, a higher baseline child BMI-Z during the preschool period was associated with the emergence of obesity 3 years later, but baseline methylation of NRF1 was associated with later obesity even after adjusting for child baseline BMI-Z.

CONCLUSIONS

Saliva offers a non-invasive means of DNA collection and epigenetic analysis. Our proof of principle study provides sound empirical evidence supporting DNA methylation in salivary tissue as a potential predictor of subsequent childhood obesity for Hispanic children. NFR1 could be a target for further exploration of obesity in this population.

The Bcl-2 homologue Buffy rescues α-synuclein-induced Parkinson disease-like phenotypes in Drosophila

Background

In contrast to the complexity found in mammals, only two Bcl-2 family genes have been found in Drosophila melanogaster including the pro-cell survival, human Bok-related orthologue, Buffy. The directed expression of α-synuclein, the first gene identified to contribute to inherited forms of Parkinson disease (PD), in the dopaminergic neurons (DA) of flies has provided a robust and well-studied Drosophila model of PD complete with the loss of neurons and accompanying motor defects. To more fully understand the biological basis of Bcl-2 genes in PD, we altered the expression of Buffy in the dopamine producing neurons with and without the expression of α-synuclein, and in the developing neuron-rich eye.

Results

To alter the expression of Buffy in the dopaminergic neurons of Drosophila, the Ddc-Gal4 transgene was used. The directed expression of Buffy in the dopamine producing neurons resulted in flies with increased climbing ability and enhanced survival, while the inhibition of Buffy in the dopaminergic neurons reduced climbing ability over time prematurely, similar to the phenotype observed in the α-synuclein-induced Drosophila model of PD. Subsequently, the expression of Buffy was altered in the α-synuclein-induced Drosophila model of PD. Analysis revealed that Buffy acted to rescue the associated loss of locomotor ability observed in the α-synuclein-induced model of PD, while Buffy RNA interference resulted in an enhanced α-synuclein-induced loss of climbing ability. In complementary experiments the overexpression of Buffy in the developing eye suppressed the mild rough eye phenotype that results from Gal4 expression and from α-synuclein expression. When Buffy is inhibited the roughened eye phenotype is enhanced.

Conclusions

The inhibition of Buffy in DA neurons produces a novel model of PD in Drosophila. The directed expression of Buffy in DA neurons provide protection and counteracts the α-synuclein-induced Parkinson disease-like phenotypes. Taken all together this demonstrates a role for Buffy, a Bcl-2 pro-cell survival gene, in neuroprotection.

Cell death regulates muscle fiber number

Cell death can have both cell autonomous and non-autonomous roles in normal development. Previous studies have shown that the central cell death regulators grim and reaper are required for the developmentally important elimination of stem cells and neurons in the developing central nervous system (CNS). Here we show that cell death in the nervous system is also required for normal muscle development. In the absence of grim and reaper, there is an increase in the number of fibers in the ventral abdominal muscles in the Drosophila adult. This phenotype can be partially recapitulated by inhibition of cell death specifically in the CNS, indicating a non-autonomous role for neuronal death in limiting muscle fiber number. We also show that FGFs produced in the cell death defective nervous system are required for the increase in muscle fiber number. Cell death in the muscle lineage during pupal stages also plays a role in specifying fiber number. Our work suggests that FGFs from the CNS act as a survival signal for muscle founder cells. Thus, proper muscle fiber specification requires cell death in both the nervous system and in the developing muscle itself.

Screening of suppressors of bax-induced cell death identifies glycerophosphate oxidase-1 as a mediator of debcl-induced apoptosis in Drosophila

Members of the Bcl-2 family are key elements of the apoptotic machinery. In mammals, this multigenic family contains about twenty members, which either promote or inhibit apoptosis. We have previously shown that the mammalian pro-apoptotic Bcl-2 family member Bax is very efficient in inducing apoptosis in Drosophila, allowing the study of bax-induced cell death in a genetic animal model. We report here the results of the screening of a P[UAS]-element insertion library performed to identify gene products that modify the phenotypes induced by the expression of bax in Drosophila melanogaster. We isolated 17 putative modifiers involved in various function or process: the ubiquitin/proteasome pathway; cell growth, proliferation and death; pathfinding and cell adhesion; secretion and extracellular signaling; metabolism and oxidative stress. Most of these suppressors also inhibit debcl-induced phenotypes, suggesting that the activities of both proteins can be modulated in part by common signaling or metabolic pathways. Among these suppressors, Glycerophosphate oxidase-1 is found to participate in debcl-induced apoptosis by increasing mitochondrial reactive oxygen species accumulation.

Cell death in development: Signaling pathways and core mechanisms

Programmed cell death eliminates unneeded and dangerous cells in a timely and effective manner during development. In this review, we examine the role cell death plays during development in worms, flies and mammals. We discuss signaling pathways that regulate developmental cell death, and describe how they communicate with the core cell death pathways. In most organisms, the majority of developmental cell death is seen in the nervous system. Therefore we focus on what is known about the regulation of developmental cell death in this tissue. Understanding how the cell death is regulated during development may provide insight into how this process can be manipulated in the treatment of disease.

Dimorphic ovary differentiation in honeybee (Apis mellifera) larvae involves caste-specific expression of homologs of ark and buffy cell death genes

The establishment of the number of repeated structural units, the ovarioles, in the ovaries is one of the critical events that shape caste polyphenism in social insects. In early postembryonic development, honeybee (Apis mellifera) larvae have a pair of ovaries, each one consisting of almost two hundred ovariole primordia. While practically all these ovarioles continue developing in queen-destined larvae, they undergo massive programmed cell death (PCD) in worker-destined larvae. So as to gain insight into the molecular basis of this fundamental process in caste differentiation we used quantitative PCR (qPCR) and fluorescent in situ hybridization (FISH) to investigate the expression of the Amark and Ambuffy genes in the ovaries of the two honeybee castes throughout the fifth larval instar. These are the homologs of ark and buffy Drosophila melanogaster genes, respectively, involved in activating and inhibiting PCD. Caste-specific expression patterns were found during this time-window defining ovariole number. Amark transcript levels were increased when ovariole resorption was intensified in workers, but remained at low levels in queen ovaries. The transcripts were mainly localized at the apical end of all the worker ovarioles, but appeared in only a few queen ovarioles, thus strongly suggesting a function in mediating massive ovariolar cell death in worker larvae. Ambuffy was mainly expressed in the peritoneal sheath cells covering each ovariole. The levels of Ambuffy transcripts increased earlier in the developing ovaries of queens than in workers. Consistent with a protective role against cell death, Ambuffy transcripts were localized in practically all queen ovarioles, but only in few worker ovarioles. The results are indicative of a functional relationship between the expression of evolutionary conserved cell death genes and the morphological events leading to caste-specific ovary differentiation in a social insect.

Caspase-dependent regulation of the ubiquitin-proteasome system through direct substrate targeting

Drosophila inhibitor of apoptosis (IAP) 1 (DIAP1) is an E3 ubiquitin ligase that regulates apoptosis in flies, in large part through direct inhibition and/or ubiquitinylation of caspases. IAP antagonists, such as Reaper, Hid, and Grim, are thought to induce cell death by displacing active caspases from baculovirus IAP repeat domains in DIAP1, but can themselves become targets of DIAP1-mediated ubiquitinylation. Herein, we demonstrate that Grim self-associates in cells and is ubiquitinylated by DIAP1 at Lys136 in an UbcD1-dependent manner, resulting in its rapid turnover. K48-linked ubiquitin chains are added almost exclusively to BIR2-bound Grim as a result of its structural proximity to DIAP1's RING domain. However, active caspases can simultaneously cleave Grim at Asp132, removing the lysine necessary for ubiquitinylation as well as any existing ubiquitin conjugates. Cleavage therefore enhances the stability of Grim and initiates a feed-forward caspase amplification loop, resulting in greater cell death. In summary, Grim is a caspase substrate whose cleavage promotes apoptosis by limiting, in a target-specific fashion, its ubiquitinylation and turnover by the proteasome.

Essential role of grim-led programmed cell death for the establishment of corazonin-producing peptidergic nervous system during embryogenesis and metamorphosis in Drosophila melanogaster

In Drosophila melanogaster, combinatorial activities of four death genes, head involution defective (hid), reaper (rpr), grim, and sickle (skl), have been known to play crucial roles in the developmentally regulated programmed cell death (PCD) of various tissues. However, different expression patterns of the death genes also suggest distinct functions played by each. During early metamorphosis, a great number of larval neurons unfit for adult life style are removed by PCD. Among them are eight pairs of corazonin-expressing larval peptidergic neurons in the ventral nerve cord (vCrz). To reveal death genes responsible for the PCD of vCrz neurons, we examined extant and recently available mutations as well as RNA interference that disrupt functions of single or multiple death genes. We found grim as a chief proapoptotic gene and skl and rpr as minor ones. The function of grim is also required for PCD of the mitotic sibling cells of the vCrz neuronal precursors (EW3-sib) during embryonic neurogenesis. An intergenic region between grim and rpr, which, it has been suggested, may enhance expression of three death genes in embryonic neuroblasts, appears to play a role for the vCrz PCD, but not for the EW3-sib cell death. The death of vCrz neurons and EW3-sib is triggered by ecdysone and the Notch signaling pathway, respectively, suggesting distinct regulatory mechanisms of grim expression in a cell- and developmental stage-specific manner.

The dREAM/Myb-MuvB complex and Grim are key regulators of the programmed death of neural precursor cells at the Drosophila posterior wing margin

Successful development of a multicellular organism depends on the finely tuned orchestration of cell proliferation, differentiation and apoptosis from embryogenesis through adulthood. The MYB-gene family encodes sequence-specific DNA-binding transcription factors that have been implicated in the regulation of both normal and neoplastic growth. The Drosophila Myb protein, DMyb (and vertebrate B-Myb protein), has been shown to be part of the dREAM/MMB complex, a large multi-subunit complex, which in addition to four Myb-interacting proteins including Mip130, contains repressive E2F and pRB proteins. This complex has been implicated in the regulation of DNA replication within the context of chorion gene amplification and transcriptional regulation of a wide array of genes. Detailed phenotypic analysis of mutations in the Drosophila myb gene, Dm myb, has revealed a previously undiscovered function for the dREAM/MMB complex in regulating programmed cell death (PCD). In cooperation with the pro-apoptotic protein Grim and dREAM/MMB, DMyb promotes the PCD of specified sensory organ precursor daughter cells in at least two different settings in the peripheral nervous system: the pIIIb precursor of the neuron and sheath cells in the posterior wing margin and the glial cell in the thoracic microchaete lineage. Unlike previously analyzed settings, in which the main role of DMyb has been to antagonize the activities of other dREAM/MMB complex members, it appears to be the critical effector in promoting PCD. The finding that Dm myb and grim are both involved in regulating PCD in two distinct settings suggests that these two genes may often work together to mediate PCD.

Multipolar functions of BCL-2 proteins link energetics to apoptosis

Classical apoptotic cell death is now sufficiently well understood to be interrogated with mathematical modeling and manipulated with targeted drugs for clinical benefit. However, a biological black hole has emerged with the realization that apoptosis regulators are functionally multipolar. BCL-2 family proteins appear to have much greater effects on cells than can be explained by their known roles in apoptosis. Although these effects may be observable simply because the cell is not dead, the general assumption is that BCL-2 proteins have undiscovered biochemical activities. Conversely, these as yet uncharacterized day-jobs also may underlie their profound effects on cell survival, challenging current assumptions about classical apoptosis. Even their sub-mitochondrial localizations remain controversial. Here we attempt to integrate seemingly conflicting information with the prospect that BCL-2 proteins themselves may be the critical crosstalk between life and death.

BAX inhibitor-1 regulates autophagy by controlling the IRE1α branch of the unfolded protein response

Both autophagy and apoptosis are tightly regulated processes playing a central role in tissue homeostasis. Bax inhibitor 1 (BI-1) is a highly conserved protein with a dual role in apoptosis and endoplasmic reticulum (ER) stress signalling through the regulation of the ER stress sensor inositol requiring kinase 1 α (IRE1α). Here, we describe a novel function of BI-1 in the modulation of autophagy. BI-1-deficient cells presented a faster and stronger induction of autophagy, increasing LC3 flux and autophagosome formation. These effects were associated with enhanced cell survival under nutrient deprivation. Repression of autophagy by BI-1 was dependent on cJun-N terminal kinase (JNK) and IRE1α expression, possibly due to a displacement of TNF-receptor associated factor-2 (TRAF2) from IRE1α. Targeting BI-1 expression in flies altered autophagy fluxes and salivary gland degradation. BI-1 deficiency increased flies survival under fasting conditions. Increased expression of autophagy indicators was observed in the liver and kidney of bi-1-deficient mice. In summary, we identify a novel function of BI-1 in multicellular organisms, and suggest a critical role of BI-1 as a stress integrator that modulates autophagy levels and other interconnected homeostatic processes.

Coordinated expression of cell death genes regulates neuroblast apoptosis

Properly regulated apoptosis in the developing central nervous system is crucial for normal morphogenesis and homeostasis. In Drosophila, a subset of neural stem cells, or neuroblasts, undergo apoptosis during embryogenesis. Of the 30 neuroblasts initially present in each abdominal hemisegment of the embryonic ventral nerve cord, only three survive into larval life, and these undergo apoptosis in the larvae. Here, we use loss-of-function analysis to demonstrate that neuroblast apoptosis during embryogenesis requires the coordinated expression of the cell death genes grim and reaper, and possibly sickle. These genes are clustered in a 140 kb region of the third chromosome and show overlapping patterns of expression. We show that expression of grim, reaper and sickle in embryonic neuroblasts is controlled by a common regulatory region located between reaper and grim. In the absence of grim and reaper, many neuroblasts survive the embryonic period of cell death and the ventral nerve cord becomes massively hypertrophic. Deletion of grim alone blocks the death of neuroblasts in the larvae. The overlapping activity of these multiple cell death genes suggests that the coordinated regulation of their expression provides flexibility in this crucial developmental process.

Steroid-triggered, cell-autonomous death of a Drosophila motoneuron during metamorphosis

BACKGROUND

The metamorphosis of Drosophila melanogaster is accompanied by elimination of obsolete neurons via programmed cell death (PCD). Metamorphosis is regulated by ecdysteroids, including 20-hydroxyecdysone (20E), but the roles and modes of action of hormones in regulating neuronal PCD are incompletely understood.

RESULTS

We used targeted expression of GFP to track the fate of a larval motoneuron, RP2, in ventral ganglia. RP2s in abdominal neuromeres two through seven (A2 to A7) exhibited fragmented DNA by 15 hours after puparium formation (h-APF) and were missing by 20 h-APF. RP2 death began shortly after the 'prepupal pulse' of ecdysteroids, during which time RP2s expressed ecdysteroid receptors (EcRs). Genetic manipulations showed that RP2 death required the function of EcR-B isoforms, the death-activating gene, reaper (but not hid), and the apoptosome component, Dark. PCD was blocked by expression of the caspase inhibitor p35 but unaffected by manipulating Diap1. In contrast, aCC motoneurons in neuromeres A2 to A7, and RP2s in neuromere A1, expressed EcRs during the prepupal pulse but survived into the pupal stage under all conditions tested. To test the hypothesis that ecdysteroids trigger RP2's death directly, we placed abdominal GFP-expressing neurons in cell culture immediately prior to the prepupal pulse, with or without 20E. 20E induced significant PCD in putative RP2s, but not in control neurons, as assessed by morphological criteria and propidium iodide staining.

CONCLUSIONS

These findings suggest that the rise of ecdysteroids during the prepupal pulse acts directly, via EcR-B isoforms, to activate PCD in RP2 motoneurons in abdominal neuromeres A2 to A7, while sparing RP2s in A1. Genetic manipulations suggest that RP2's death requires Reaper function, apoptosome assembly and Diap1-independent caspase activation. RP2s offer a valuable 'single cell' approach to the molecular understanding of neuronal death during insect metamorphosis and, potentially, of neurodegeneration in other contexts.

Bcl-2 proteins and autophagy regulate mitochondrial dynamics during programmed cell death in the Drosophila ovary

The Bcl-2 family has been shown to regulate mitochondrial dynamics during cell death in mammals and C. elegans, but evidence for this in Drosophila has been elusive. Here, we investigate the regulation of mitochondrial dynamics during germline cell death in the Drosophila melanogaster ovary. We find that mitochondria undergo a series of events during the progression of cell death, with remodeling, cluster formation and uptake of clusters by somatic follicle cells. These mitochondrial dynamics are dependent on caspases, the Bcl-2 family, the mitochondrial fission and fusion machinery, and the autophagy machinery. Furthermore, Bcl-2 family mutants show a striking defect in cell death in the ovary. These data indicate that a mitochondrial pathway is a major mechanism for activation of cell death in Drosophila oogenesis.

Mitochondrial involvement in cell death of non-mammalian eukaryotes

Although mitochondria are essential organelles for long-term survival of eukaryotic cells, recent discoveries in biochemistry and genetics have advanced our understanding of the requirements for mitochondria in cell death. Much of what we understand about cell death is based on the identification of conserved cell death genes in Drosophila melanogaster and Caenorhabditis elegans. However, the role of mitochondria in cell death in these models has been much less clear. Considering the active role that mitochondria play in apoptosis in mammalian cells, the mitochondrial contribution to cell death in non-mammalian systems has been an area of active investigation. In this article, we review the current research on this topic in three non-mammalian models, C. elegans, Drosophila, and Saccharomyces cerevisiae. In addition, we discuss how non-mammalian models have provided important insight into the mechanisms of human disease as they relate to the mitochondrial pathway of cell death. The unique perspective derived from each of these model systems provides a more complete understanding of mitochondria in programmed cell death. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.

Drosophila IAP antagonists form multimeric complexes to promote cell death

Self- and hetero-association of the pro-apoptotic proteins Reaper, Hid, and Grim is required for efficient induction of the cell death program.

Apoptosis is a specific form of cell death that is important for normal development and tissue homeostasis. Caspases are critical executioners of apoptosis, and living cells prevent their inappropriate activation through inhibitor of apoptosis proteins (IAPs). In Drosophila, caspase activation depends on the IAP antagonists, Reaper (Rpr), Head involution defective (Hid), and Grim. These proteins share a common motif to bind Drosophila IAP1 (DIAP1) and have partially redundant functions. We now show that IAP antagonists physically interact with each other. Rpr is able to self-associate and also binds to Hid and Grim. We have defined the domain involved in self-association and demonstrate that it is critical for cell-killing activity in vivo. In addition, we show that Rpr requires Hid for recruitment to the mitochondrial membrane and for efficient induction of cell death in vivo. Both targeting of Rpr to mitochondria and forced dimerization strongly promotes apoptosis. Our results reveal the functional importance of a previously unrecognized multimeric IAP antagonist complex for the induction of apoptosis.