DNA double-strand break-induced phosphorylation of Drosophila histone variant H2Av helps prevent radiation-induced apoptosis

Werner syndrome exonuclease promotes gut regeneration and causes age-associated gut hyperplasia in Drosophila

Human Werner syndrome (adult progeria, a well-established model of human aging) is caused by mutations in the Werner syndrome (WRN) gene. However, the expression patterns and functions of WRN in natural aging remain poorly understood. Despite the link between WRN deficiencies and progeria, our analyses of human colon tissues, mouse crypts, and Drosophila midguts revealed that WRN expression does not decrease but rather increases in intestinal stem cells (ISCs) with aging. Mechanistically, we found that the Drosophila WRN homologue (WRNexo) binds to Heat shock 70-kDa protein cognate 3 (Hsc70-3/Bip) to regulate the unfolded protein response of the endoplasmic reticulum (UPRER). Activation of the WRNexo-mediated UPRER in ISCs is required for ISC proliferation during injury repair. However, persistent DNA damage during aging leads to chronic upregulation of WRNexo in ISCs, where excessive WRNexo-induced ER stress drives age-associated gut hyperplasia in Drosophila. This study reveals how elevated WRNexo contributes to stem cell aging, providing new insights into organ aging and the pathogenesis of age-related diseases, such as colon cancer.

Tau reduction impairs nephrocyte function in Drosophila

Tau, a microtubule-associated protein, is known for its significant involvement in neurodegenerative diseases. While various molecular and immunohistochemical techniques have confirmed the presence of Tau in podocytes, its precise function within these cells remains elusive. In this study, we investigate the role of Tau in kidney podocytes using Drosophila pericardial nephrocytes as a model. We found that knockdown of Drosophila Tau in nephrocytes resulted in apoptotic cell death and the disruption of nephrocyte structure. Furthermore, we observed that decreased Tau levels induced genomic damage and abnormal distribution of γ-H2Av, altering nuclei architecture in nephrocytes, and affecting the nuclear membrane structure by interfering with lamin with aging. Additionally, Tau knockdown led to a reduction in lipid droplets in Drosophila fat body tissues, suggesting a potential role of Tau in inter-organ communication. These findings underscore the importance of Tau in the nephrocytes of Drosophila, and advocate further research to broaden our understanding of podocyte biology in kidney diseases. [BMB Reports 2025; 58(4): 169-174].

Replication stress promotes cellular transformation in Drosophila epithelium

The accurate control of DNA replication is crucial for the maintenance of genomic stability and cell viability. In this study, we explore the consequences of depleting the replicative DNA Polymerase α (POLA) in the wing disc of Drosophila melanogaster. Our findings reveal that reduced POLA activity induces DNA replication stress and activates the replication checkpoint in vivo. Consistent with this, we demonstrate that dATR, a key component in DNA replication checkpoint signaling, is essential for the maintenance of tissue integrity under conditions of compromised POLA activity. We show that cells within the wing disc exhibiting reduced POLA activity arrest in the G2 phase and undergo p53-dependent apoptosis. We also reveal a critical role for DNA Ligase 4 in sustaining cell viability when POLA function is impaired. Most notably, we report the appearance of oncogenic traits in wing disc cells with diminished POLA activity when apoptosis is suppressed. In this context, the overexpression of the oncogene cdc25/string enhances the oncogenic phenotype. These results indicate that a combination of oncogenic activation, replication stress, and suppression of apoptosis is sufficient to promote the emergence of hallmarks of tumorigenesis, highlighting major implications for cancer development in humans.

Histone Phosphorylation in DNA Damage Response

The DNA damage response (DDR) is crucial for maintaining genomic stability and preventing the accumulation of mutations that can lead to various diseases, including cancer. The DDR is a complex cellular regulatory network that involves DNA damage sensing, signal transduction, repair, and cell cycle arrest. Modifications in histone phosphorylation play important roles in these processes, facilitating DNA repair factor recruitment, damage signal transduction, chromatin remodeling, and cell cycle regulation. The precise regulation of histone phosphorylation is critical for the effective repair of DNA damage, genomic integrity maintenance, and the prevention of diseases such as cancer, where DNA repair mechanisms are often compromised. Thus, understanding histone phosphorylation in the DDR provides insights into DDR mechanisms and offers potential therapeutic targets for diseases associated with genomic instability, including cancers.

Increased levels of lagging strand polymerase α in an adult stem cell lineage affect replication-coupled histone incorporation

Stem cells display asymmetric histone inheritance, while nonstem progenitor cells exhibit symmetric patterns in the Drosophila male germ line. Here, we report that components involved in lagging strand synthesis, DNA polymerases α and δ, have substantially reduced levels in stem cells compared to progenitor cells, and this promotes local asymmetry of parental histone incorporation at the replication fork. Compromising Polα genetically induces the local replication-coupled histone incorporation pattern in progenitor cells to resemble that in stem cells, seen by both nuclear localization patterns and chromatin fibers. This is recapitulated using a Polα inhibitor in a concentration-dependent manner. The local old versus new histone asymmetry is comparable between stem cells and progenitor cells at both S phase and M phase. Together, these results indicate that developmentally programmed expression of key DNA replication components is important to shape stem cell chromatin. Furthermore, manipulating one crucial DNA replication component can induce replication-coupled histone dynamics in nonstem cells to resemble those in stem cells.

The histone demethylase dLsd1 regulates organ size by silencing transposable elements

The specific role of chromatin modifying factors in the timely execution of transcriptional changes in gene expression to regulate organ size remains largely unknown. Here, we report that in Drosophila melanogaster depletion of the histone demethylase dLsd1 results in the reduction of wing size. dLsd1 depletion affects cell proliferation and causes an increase in DNA damage and cell death. Mechanistically, we have identified Transposable Elements (TEs) as critical dLsd1 targets for organ size determination. We found that upon dLsd1 loss many TE families are upregulated, and new TE insertions appear. By blocking this new TE activity, we could rescue the wing size phenotype. Collectively, our results reveal that the histone demethylase dLsd1 and maintenance of TE homeostasis are required to ensure proper wing size.

The transmembrane protein Syndecan is required for stem cell survival and maintenance of their nuclear properties

Tissue maintenance is underpinned by resident stem cells whose activity is modulated by microenvironmental cues. Using Drosophila as a simple model to identify regulators of stem cell behaviour and survival in vivo, we have identified novel connections between the conserved transmembrane proteoglycan Syndecan, nuclear properties and stem cell function. In the Drosophila midgut, Syndecan depletion in intestinal stem cells results in their loss from the tissue, impairing tissue renewal. At the cellular level, Syndecan depletion alters cell and nuclear shape, and causes nuclear lamina invaginations and DNA damage. In a second tissue, the developing Drosophila brain, live imaging revealed that Syndecan depletion in neural stem cells results in nuclear envelope remodelling defects which arise upon cell division. Our findings reveal a new role for Syndecan in the maintenance of nuclear properties in diverse stem cell types.

Studying Cellular Senescence Using the Model Organism Drosophila melanogaster

Cellular senescence, a complex biological process characterized by irreversible cell cycle arrest, contributes significantly to the development and progression of aging and of age-related diseases. Studying cellular senescence in vivo can be challenging due to the high heterogeneity and dynamic nature of senescent cells. Recently, Drosophila melanogaster has emerged as a powerful model organism for studying aging and cellular senescence due to its tractability and short lifespan, as well as due to the conservation of age-related genes and of key age-related pathways with mammals. Consequently, several research studies have utilized Drosophila to investigate the cellular mechanisms and pathways implicated in cellular senescence. Herein, we provide an overview of the assays that can be applied to study the different features of senescent cells in D. melanogaster tissues, highlighting the benefits of this model in aging research. We also emphasize the importance of selecting appropriate biomarkers for the identification of senescent cells, and the need for further understanding of the aging process including a more accurate identification and detection of senescent cells at the organismal level; a far more complex process as compared to single cells.

Regeneration following tissue necrosis is mediated by non-apoptotic caspase activity

Tissue necrosis is a devastating complication for many human diseases and injuries. Unfortunately, our understanding of necrosis and how it impacts surrounding healthy tissue - an essential consideration when developing effective methods to treat such injuries - has been limited by a lack of robust genetically tractable models. Our lab previously established a method to study necrosis-induced regeneration in the Drosophila wing imaginal disc, which revealed a unique phenomenon whereby cells at a distance from the injury upregulate caspase activity in a process called Necrosis-induced Apoptosis (NiA) that is vital for regeneration. Here we have further investigated this phenomenon, showing that NiA is predominantly associated with the highly regenerative pouch region of the disc, shaped by genetic factors present in the presumptive hinge. Furthermore, we find that a proportion of NiA fail to undergo apoptosis, instead surviving effector caspase activation to persist within the tissue and stimulate reparative proliferation late in regeneration. This proliferation relies on the initiator caspase Dronc, and occurs independent of JNK, ROS or mitogens associated with the previously characterized Apoptosis-induced Proliferation (AiP) mechanism. These data reveal a new means by which non-apoptotic Dronc signaling promotes regenerative proliferation in response to necrotic damage.

Running the gauntlet: challenges to genome integrity in spermiogenesis

Species' continuity depends on gametogenesis to produce the only cell types that can transmit genetic information across generations. Spermiogenesis, which encompasses post-meiotic, haploid stages of male gametogenesis, is a process that leads to the formation of sperm cells well-known for their motility. Spermiogenesis faces three major challenges. First, after two rounds of meiotic divisions, the genome lacks repair templates (no sister chromatids, no homologous chromosomes), making it incredibly vulnerable to any genomic insults over an extended time (typically days-weeks). Second, the sperm genome becomes transcriptionally silent, making it difficult to respond to new perturbations as spermiogenesis progresses. Third, the histone-to-protamine transition, which is essential to package the sperm genome, counterintuitively involves DNA break formation. How spermiogenesis handles these challenges remains poorly understood. In this review, we discuss each challenge and their intersection with the biology of protamines. Finally, we discuss the implication of protamines in the process of evolution.

Transcriptomic analysis of meiotic genes during the mitosis-to-meiosis transition in Drosophila females

Germline cells produce gametes, which are specialized cells essential for sexual reproduction. Germline cells first amplify through several rounds of mitosis before switching to the meiotic program, which requires specific sets of proteins for DNA recombination, chromosome pairing, and segregation. Surprisingly, we previously found that some proteins of the synaptonemal complex, a prophase I meiotic structure, are already expressed and required in the mitotic region of Drosophila females. Here, to assess if additional meiotic genes were expressed earlier than expected, we isolated mitotic and meiotic cell populations to compare their RNA content. Our transcriptomic analysis reveals that all known meiosis I genes are already expressed in the mitotic region; however, only some of them are translated. As a case study, we focused on mei-W68, the Drosophila homolog of Spo11, to assess its expression at both the mRNA and protein levels and used different mutant alleles to assay for a premeiotic function. We could not detect any functional role for Mei-W68 during homologous chromosome pairing in dividing germ cells. Our study paves the way for further functional analysis of meiotic genes expressed in the mitotic region.

Tolerance thresholds underlie responses to DNA damage during germline development

Selfish DNA modules like transposable elements (TEs) are particularly active in the germline, the lineage that passes genetic information across generations. New TE insertions can disrupt genes and impair the functionality and viability of germ cells. However, we found that in P-M hybrid dysgenesis in Drosophila, a sterility syndrome triggered by the P-element DNA transposon, germ cells harbor unexpectedly few new TE insertions despite accumulating DNA double-strand breaks (DSBs) and inducing cell cycle arrest. Using an engineered CRISPR-Cas9 system, we show that generating DSBs at silenced P-elements or other noncoding sequences is sufficient to induce germ cell loss independently of gene disruption. Indeed, we demonstrate that both developing and adult mitotic germ cells are sensitive to DSBs in a dosage-dependent manner. Following the mitotic-to-meiotic transition, however, germ cells become more tolerant to DSBs, completing oogenesis regardless of the accumulated genome damage. Our findings establish DNA damage tolerance thresholds as crucial safeguards of genome integrity during germline development.

Senescent glia link mitochondrial dysfunction and lipid accumulation

Senescence is a cellular state linked to ageing and age-onset disease across many mammalian species1,2. Acutely, senescent cells promote wound healing3,4 and prevent tumour formation5; but they are also pro-inflammatory, thus chronically exacerbate tissue decline. Whereas senescent cells are active targets for anti-ageing therapy6-11, why these cells form in vivo, how they affect tissue ageing and the effect of their elimination remain unclear12,13. Here we identify naturally occurring senescent glia in ageing Drosophila brains and decipher their origin and influence. Using Activator protein 1 (AP1) activity to screen for senescence14,15, we determine that senescent glia can appear in response to neuronal mitochondrial dysfunction. In turn, senescent glia promote lipid accumulation in non-senescent glia; similar effects are seen in senescent human fibroblasts in culture. Targeting AP1 activity in senescent glia mitigates senescence biomarkers, extends fly lifespan and health span, and prevents lipid accumulation. However, these benefits come at the cost of increased oxidative damage in the brain, and neuronal mitochondrial function remains poor. Altogether, our results map the trajectory of naturally occurring senescent glia in vivo and indicate that these cells link key ageing phenomena: mitochondrial dysfunction and lipid accumulation.

Transcriptional programs mediating neuronal toxicity and altered glial-neuronal signaling in a Drosophila knock-in tauopathy model

Missense mutations in the gene encoding the microtubule-associated protein TAU (current and approved symbol is MAPT) cause autosomal dominant forms of frontotemporal dementia. Multiple models of frontotemporal dementia based on transgenic expression of human TAU in experimental model organisms, including Drosophila, have been described. These models replicate key features of the human disease but do not faithfully recreate the genetic context of the human disorder. Here we use CRISPR-Cas-mediated gene editing to model frontotemporal dementia caused by the TAU P301L mutation by creating the orthologous mutation, P251L, in the endogenous Drosophila tau gene. Flies heterozygous or homozygous for Tau P251L display age-dependent neurodegeneration, display metabolic defects, and accumulate DNA damage in affected neurons. To understand the molecular events promoting neuronal dysfunction and death in knock-in flies, we performed single-cell RNA sequencing on approximately 130,000 cells from brains of Tau P251L mutant and control flies. We found that expression of disease-associated mutant tau altered gene expression cell autonomously in all neuronal cell types identified. Gene expression was also altered in glial cells, suggestive of non-cell-autonomous regulation. Cell signaling pathways, including glial-neuronal signaling, were broadly dysregulated as were brain region and cell type-specific protein interaction networks and gene regulatory programs. In summary, we present here a genetic model of tauopathy that faithfully recapitulates the genetic context and phenotypic features of the human disease, and use the results of comprehensive single-cell sequencing analysis to outline pathways of neurotoxicity and highlight the potential role of non-cell-autonomous changes in glia.

The endogenous antioxidant ability of royal jelly in Drosophila is independent of Keap1/Nrf2 by activating oxidoreductase activity

Royal jelly (RJ) is a biologically active substance secreted by the hypopharyngeal and mandibular glands of worker honeybees. It is widely claimed that RJ reduces oxidative stress. However, the antioxidant activity of RJ has mostly been determined by in vitro chemical detection methods or by external administration drugs that cause oxidative stress. Whether RJ can clear the endogenous production of reactive oxygen species (ROS) in cells remains largely unknown. Here, we systematically investigated the antioxidant properties of RJ using several endogenous oxidative stress models of Drosophila. We found that RJ enhanced sleep quality of aging Drosophila, which is decreased due to an increase of oxidative damage with age. RJ supplementation improved survival and suppressed ROS levels in gut cells of flies upon exposure to hydrogen peroxide or to the neurotoxic agent paraquat. Moreover, RJ supplementation moderated levels of ROS in endogenous gut cells and extended lifespan after exposure of flies to heat stress. Sleep deprivation leads to accumulation of ROS in the gut cells, and RJ attenuated the consequences of oxidative stress caused by sleep loss and prolonged lifespan. Mechanistically, RJ prevented cell oxidative damage caused by heat stress or sleep deprivation, with the antioxidant activity in vivo independent of Keap1/Nrf2 signaling. RJ supplementation activated oxidoreductase activity in the guts of flies, suggesting its ability to inhibit endogenous oxidative stress and maintain health, possibly in humans.

Senescent cells and macrophages cooperate through a multi-kinase signaling network to promote intestinal transformation in Drosophila

Cellular senescence is a conserved biological process that plays a crucial and context-dependent role in cancer. The highly heterogeneous and dynamic nature of senescent cells and their small numbers in tissues make in vivo mechanistic studies of senescence challenging. As a result, how multiple senescence-inducing signals are integrated in vivo to drive senescence in only a small number of cells is unclear. Here, we identify cells that exhibit multiple features of senescence in a Drosophila model of intestinal transformation, which emerge in response to concurrent activation of AKT, JNK, and DNA damage signaling within transformed tissue. Eliminating senescent cells, genetically or by treatment with senolytic compounds, reduces overgrowth and improves survival. We find that senescent cells promote tumorigenesis by recruiting Drosophila macrophages to the transformed tissue, which results in non-autonomous activation of JNK signaling. These findings identify senescent cell-macrophage interactions as an important driver of epithelial transformation.

Transcriptional programs mediating neuronal toxicity and altered glial-neuronal signaling in a Drosophila knock-in tauopathy model

Missense mutations in the gene encoding the microtubule-associated protein tau cause autosomal dominant forms of frontotemporal dementia. Multiple models of frontotemporal dementia based on transgenic expression of human tau in experimental model organisms, including Drosophila, have been described. These models replicate key features of the human disease, but do not faithfully recreate the genetic context of the human disorder. Here we use CRISPR-Cas mediated gene editing to model frontotemporal dementia caused by the tau P301L mutation by creating the orthologous mutation, P251L, in the endogenous Drosophila tau gene. Flies heterozygous or homozygous for tau P251L display age-dependent neurodegeneration, metabolic defects and accumulate DNA damage in affected neurons. To understand the molecular events promoting neuronal dysfunction and death in knock-in flies we performed single-cell RNA sequencing on approximately 130,000 cells from brains of tau P251L mutant and control flies. We found that expression of disease-associated mutant tau altered gene expression cell autonomously in all neuronal cell types identified and non-cell autonomously in glial cells. Cell signaling pathways, including glial-neuronal signaling, were broadly dysregulated as were brain region and cell-type specific protein interaction networks and gene regulatory programs. In summary, we present here a genetic model of tauopathy, which faithfully recapitulates the genetic context and phenotypic features of the human disease and use the results of comprehensive single cell sequencing analysis to outline pathways of neurotoxicity and highlight the role of non-cell autonomous changes in glia.

ATM/Chk2 and ATR/Chk1 Pathways Respond to DNA Damage Induced by Movento® 240SC and Envidor® 240SC Keto-Enol Insecticides in the Germarium of Drosophila melanogaster

DNA damage response (DDR) pathways in keto-enol genotoxicity have not been characterized, and few studies have reported genotoxic effects in non-target organisms. The present study shows that concentrations of 11.2, 22.4, 37.3 mg/L of Movento® 240SC and 12.3, 24.6, 41.1 mg/L of Envidor® 240SC for 72 h oral exposure induced DSBs by significantly increasing the percentage of γH2AV expression in regions 2b and 3 from the germarium of wild type females of Drosophila melanogaster Oregon R, compared to the control group (0.0 mg/L of insecticides), via confocal immunofluorescence microscopy. The comparison between both insecticides' reveals that only the Envidor® 240SC induces concentration-dependent DNA damage, as well as structural changes in the germarium. We determined that the DDR induced by Movento® 240SC depends on the activation of the ATMtefu, Chk1grp and Chk2lok kinases by significantly increasing the percentage of expression of γH2AV in regions 2b and 3 of the germarium, and that ATRmei-29D and p53dp53 kinases only respond at the highest concentration of 37.3 mg/L of Movento® 240SC. With the Envidor® 240SC insecticide, we determined that the DDR depends on the activation of the ATRmei-29D/Chk1grp and ATMtefu/Chk2lok kinases, and p53dp53 by significantly increasing the percentage of expression of γH2AV in the germarium.

Senescent cells and macrophages cooperate through a multi-kinase signaling network to promote intestinal transformation in Drosophila

Cellular senescence is a conserved biological process essential for embryonic development, tissue remodeling, repair, and a key regulator of aging. Senescence also plays a crucial role in cancer, though this role can be tumor-suppressive or tumor-promoting, depending on the genetic context and the microenvironment. The highly heterogeneous, dynamic, and context-dependent nature of senescence-associated features and the relatively small numbers of senescent cells in tissues makes in vivo mechanistic studies of senescence challenging. As a result, which senescence-associated features are observed in which disease contexts and how they contribute to disease phenotypes remain largely unknown. Similarly, the specific mechanisms by which various senescence-inducing signals are integrated in vivo to induce senescence and why some cells become senescent while their immediate neighbors do not are unclear. Here, we identify a small number of cells that exhibit multiple features of senescence in a genetically complex model of intestinal transformation we recently established in the developing Drosophila larval hindgut epithelium. We demonstrate that these cells emerge in response to concurrent activation of AKT, JNK, and DNA damage response pathways within transformed tissue. Eliminating senescent cells, genetically or by treatment with senolytic compounds, reduces overgrowth and improves survival. We find that this tumor-promoting role is mediated by Drosophila macrophages recruited to the transformed tissue by senescent cells, which results in non-autonomous activation of JNK signaling within the transformed epithelium. These findings emphasize complex cell-cell interactions underlying epithelial transformation and identify senescent cell-macrophage interactions as a potential druggable node in cancer.

Distinct signaling signatures drive compensatory proliferation via S-phase acceleration

Regeneration relies on cell proliferation to restore damaged tissues. Multiple signaling pathways activated by local or paracrine cues have been identified to promote regenerative proliferation. How different types of tissue damage may activate distinct signaling pathways and how these differences converge on regenerative proliferation is less well defined. To better understand how tissue damage and proliferative signals are integrated during regeneration, we investigate models of compensatory proliferation in Drosophila imaginal discs. We find that compensatory proliferation is associated with a unique cell cycle profile, which is characterized by short G1 and G2 phases and, surprisingly, by acceleration of the S-phase. S-phase acceleration can be induced by two distinct signaling signatures, aligning with inflammatory and non-inflammatory tissue damage. Specifically, non-autonomous activation of JAK/STAT and Myc in response to inflammatory damage, or local activation of Ras/ERK and Hippo/Yki in response to elevated cell death, promote accelerated nucleotide incorporation during S-phase. This previously unappreciated convergence of different damaging insults on the same regenerative cell cycle program reconciles previous conflicting observations on proliferative signaling in different tissue regeneration and tumor models.

Phosphorylated histone variant γH2Av is associated with chromatin insulators in Drosophila

Chromatin insulators are responsible for orchestrating long-range interactions between enhancers and promoters throughout the genome and align with the boundaries of Topologically Associating Domains (TADs). Here, we demonstrate an association between gypsy insulator proteins and the phosphorylated histone variant H2Av (γH2Av), normally a marker of DNA double strand breaks. Gypsy insulator components colocalize with γH2Av throughout the genome, in polytene chromosomes and in diploid cells in which Chromatin IP data shows it is enriched at TAD boundaries. Mutation of insulator components su(Hw) and Cp190 results in a significant reduction in γH2Av levels in chromatin and phosphatase inhibition strengthens the association between insulator components and γH2Av and rescues γH2Av localization in insulator mutants. We also show that γH2Av, but not H2Av, is a component of insulator bodies, which are protein condensates that form during osmotic stress. Phosphatase activity is required for insulator body dissolution after stress recovery. Together, our results implicate the H2A variant with a novel mechanism of insulator function and boundary formation.

Low dose rate γ-irradiation protects fruit fly chromosomes from double strand breaks and telomere fusions by reducing the esi-RNA biogenesis factor Loquacious

It is still continuously debated whether the low-dose/dose-rate (LDR) of ionizing radiation represents a hazard for humans. Model organisms, such as fruit flies, are considered valuable systems to reveal insights into this issue. We found that, in wild-type Drosophila melanogaster larval neuroblasts, the frequency of Chromosome Breaks (CBs), induced by acute γ-irradiation, is considerably reduced when flies are previously exposed to a protracted dose of 0.4 Gy delivered at a dose rate of 2.5 mGy/h. This indicates that this exposure, which is associated with an increased expression of DNA damage response proteins, induces a radioadaptive response (RAR) that protects Drosophila from extensive DNA damage. Interestingly, the same exposure reduces the frequency of telomere fusions (TFs) from Drosophila telomere capping mutants suggesting that the LDR can generally promote a protective response on chromatin sites that are recognized as DNA breaks. Deep RNA sequencing revealed that RAR is associated with a reduced expression of Loquacious D (Loqs-RD) gene that encodes a well-conserved dsRNA binding protein required for esiRNAs biogenesis. Remarkably, loss of Loqs mimics the LDR-mediated chromosome protection as it decreases the IR-induced CBs and TFs frequency. Thus, our molecular characterization of RAR identifies Loqs as a key factor in the cellular response to LDR and in the epigenetic routes involved in radioresistance.

Chronic low y-radiation exposure to Drosophila cells decreases chromosome breaks induced by high-dose irradiation and telomere dysfunction by reducing the esiRNA biogenesis factor Loquacious D.

Cross-species incompatibility between a DNA satellite and the Drosophila Spartan homolog poisons germline genome integrity

Satellite DNA spans megabases of eukaryotic sequence and evolves rapidly.1-6 Paradoxically, satellite-rich genomic regions mediate strictly conserved, essential processes such as chromosome segregation and nuclear structure.7-10 A leading resolution to this paradox posits that satellite DNA and satellite-associated chromosomal proteins coevolve to preserve these essential functions.11 We experimentally test this model of intragenomic coevolution by conducting the first evolution-guided manipulation of both chromosomal protein and DNA satellite. The 359bp satellite spans an 11 Mb array in Drosophila melanogaster that is absent from its sister species, Drosophila simulans.12-14 This species-specific DNA satellite colocalizes with the adaptively evolving, ovary-enriched protein, maternal haploid (MH), the Drosophila homolog of Spartan.15 To determine if MH and 359bp coevolve, we swapped the D. simulans version of MH ("MH[sim]") into D. melanogaster. MH[sim] triggers ovarian cell death, reduced ovary size, and loss of mature eggs. Surprisingly, the D. melanogaster mh-null mutant has no such ovary phenotypes,15 suggesting that MH[sim] is toxic in a D. melanogaster background. Using both cell biology and genetics, we discovered that MH[sim] poisons oogenesis through a DNA-damage pathway. Remarkably, deleting the D. melanogaster-specific 359bp satellite array completely restores mh[sim] germline genome integrity and fertility, consistent with a history of coevolution between these two fast-evolving loci. Germline genome integrity and fertility are also restored by overexpressing topoisomerase II (Top2), suggesting that MH[sim] interferes with Top2-mediated processing of 359bp. The observed 359bp-MH[sim] cross-species incompatibility supports a model under which seemingly inert repetitive DNA and essential chromosomal proteins must coevolve to preserve germline genome integrity.

Mxc, a Drosophila homolog of mental retardation-associated gene NPAT, maintains neural stem cell fate

BACKGROUND

Mental retardation is a complex neurodevelopmental disorder. NPAT, a component of the histone locus body (HLB), has been implicated as a candidate gene for mental retardation, with a mechanism yet to be elucidated.

RESULTS

We identified that mxc, the Drosophila ortholog of NPAT, is required for the development of nervous system. Knockdown of mxc resulted in a massive loss of neurons and locomotion dysfunction in adult flies. In the mxc mutant or RNAi knockdown larval brains, the neuroblast (NB, also known as neural stem cell) cell fate is prematurely terminated and its proliferation potential is impeded concurrent with the blocking of the differentiation process of ganglion mother cells (GMCs). A reduction of transcription levels of histone genes was shown in mxc knockdown larval brains, accompanied by DNA double-strand breaks (DSBs). The subsidence of histone transcription levels leads to prematurely termination of NB cell fate and blockage of the GMC differentiation process. Our data also show that the increase in autophagy induced by mxc knockdown in NBs could be a defense mechanism in response to abnormal HLB assembly and premature termination of NB cell fate.

CONCLUSIONS

Our study demonstrate that Mxc plays a critical role in maintaining neural stem cell fate and GMC differentiation in the Drosophila larval brain. This discovery may shed light on the understanding of the pathogenesis of NPAT-related mental retardation in humans.

Identification of replication fork-associated proteins in Drosophila embryos and cultured cells using iPOND coupled to quantitative mass spectrometry

Replication of the eukaryotic genome requires the formation of thousands of replication forks that must work in concert to accurately replicate the genetic and epigenetic information. Defining replication fork-associated proteins is a key step in understanding how genomes are replicated and repaired in the context of chromatin to maintain genome stability. To identify replication fork-associated proteins, we performed iPOND (Isolation of Proteins on Nascent DNA) coupled to quantitative mass spectrometry in Drosophila embryos and cultured cells. We identified 76 and 278 fork-associated proteins in post-MZT embryos and Drosophila cultured S2 cells, respectively. By performing a targeted screen of a subset of these proteins, we demonstrate that BRWD3, a targeting specificity factor for the DDB1/Cul4 ubiquitin ligase complex (CRL4), functions at or in close proximity to replication forks to promote fork progression and maintain genome stability. Altogether, our work provides a valuable resource for those interested in DNA replication, repair and chromatin assembly during development.

Role of H2A.Z.1 in epithelial-mesenchymal transition and radiation resistance of lung adenocarcinoma in vitro

Radiation resistance reduces patient survival and is an important challenge in treating lung adenocarcinoma (LUAD). Previous studies have shown that histone H2A variants can affect the radiosensitivity of tumors; however, the main role of histone H2A variants in LUAD remains unclear. Using the TCGA database, we found that histone H2A variant H2A.Z.1 is positively associated with the progression and poor prognosis of LUAD. Colony formation, scratch wound-healing, and transwell assays as well as Western blot were performed to assess the role of H2A.Z.1 in vitro. Results suggested that H2A.Z.1 promoted cell migration and invasion, epithelial-mesenchymal transition, stemness, and radiation resistance in LUAD cells. Targeting H2A.Z.1 in combination with radiation therapy could be a potential therapeutic approach for radiation resistant LUAD.

Coordination between cell proliferation and apoptosis after DNA damage in Drosophila

Exposure to genotoxic stress promotes cell cycle arrest and DNA repair or apoptosis. These "life" or "death" cell fate decisions often rely on the activity of the tumor suppressor gene p53. Therefore, the precise regulation of p53 is essential to maintain tissue homeostasis and to prevent cancer development. However, how cell cycle progression has an impact on p53 cell fate decision-making is mostly unknown. In this work, we demonstrate that Drosophila p53 proapoptotic activity can be impacted by the G2/M kinase Cdk1. We find that cell cycle arrested or endocycle-induced cells are refractory to ionizing radiation-induced apoptosis. We show that p53 binding to the regulatory elements of the proapoptotic genes and its ability to activate their expression is compromised in experimentally arrested cells. Our results indicate that p53 genetically and physically interacts with Cdk1 and that p53 proapoptotic role is regulated by the cell cycle status of the cell. We propose a model in which cell cycle progression and p53 proapoptotic activity are molecularly connected to coordinate the appropriate response after DNA damage.

Drosophila p53 isoforms have overlapping and distinct functions in germline genome integrity and oocyte quality control

p53 gene family members in humans and other organisms encode a large number of protein isoforms whose functions are largely undefined. Using Drosophila as a model, we find that a p53B isoform is expressed predominantly in the germline where it colocalizes with p53A into subnuclear bodies. It is only p53A, however, that mediates the apoptotic response to ionizing radiation in the germline and soma. In contrast, p53A and p53B are both required for the normal repair of meiotic DNA breaks, an activity that is more crucial when meiotic recombination is defective. We find that in oocytes with persistent DNA breaks p53A is also required to activate a meiotic pachytene checkpoint. Our findings indicate that Drosophila p53 isoforms have DNA lesion and cell type-specific functions, with parallels to the functions of mammalian p53 family members in the genotoxic stress response and oocyte quality control.

Somatic piRNAs and Transposons are Differentially Expressed Coincident with Skeletal Muscle Atrophy and Programmed Cell Death

PIWI-interacting RNAs (piRNAs) are small single-stranded RNAs that can repress transposon expression via epigenetic silencing and transcript degradation. They have been identified predominantly in the ovary and testis, where they serve essential roles in transposon silencing in order to protect the integrity of the genome in the germline. The potential expression of piRNAs in somatic cells has been controversial. In the present study we demonstrate the expression of piRNAs derived from both genic and transposon RNAs in the intersegmental muscles (ISMs) from the tobacco hawkmoth Manduca sexta. These piRNAs are abundantly expressed, ∼27 nt long, map antisense to transposons, are oxidation resistant, exhibit a 5’ uridine bias, and amplify via the canonical ping-pong pathway. An RNA-seq analysis demonstrated that 19 piRNA pathway genes are expressed in the ISMs and are developmentally regulated. The abundance of piRNAs does not change when the muscles initiate developmentally-regulated atrophy, but are repressed coincident with the commitment of the muscles undergo programmed cell death at the end of metamorphosis. This change in piRNA expression is correlated with the repression of several retrotransposons and the induction of specific DNA transposons. The developmentally-regulated changes in the expression of piRNAs, piRNA pathway genes, and transposons are all regulated by 20-hydroxyecdysone, the steroid hormone that controls the timing of ISM death. Taken together, these data provide compelling evidence for the existence of piRNA in somatic tissues and suggest that they may play roles in developmental processes such as programmed cell death.

X Chromosome Inactivation during Grasshopper Spermatogenesis

Regulation of transcriptional activity during meiosis depends on the interrelated processes of recombination and synapsis. In eutherian mammal spermatocytes, transcription levels change during prophase-I, being low at the onset of meiosis but highly increased from pachytene up to the end of diplotene. However, X and Y chromosomes, which usually present unsynapsed regions throughout prophase-I in male meiosis, undergo a specific pattern of transcriptional inactivation. The interdependence of synapsis and transcription has mainly been studied in mammals, basically in mouse, but our knowledge in other unrelated phylogenetically species is more limited. To gain new insights on this issue, here we analyzed the relationship between synapsis and transcription in spermatocytes of the grasshopper Eyprepocnemis plorans. Autosomal chromosomes of this species achieve complete synapsis; however, the single X sex chromosome remains always unsynapsed and behaves as a univalent. We studied transcription in meiosis by immunolabeling with RNA polymerase II phosphorylated at serine 2 and found that whereas autosomes are active from leptotene up to diakinesis, the X chromosome is inactive throughout meiosis. This inactivation is accompanied by the accumulation of, at least, two repressive epigenetic modifications: H3 methylated at lysine 9 and H2AX phosphorylated at serine 139. Furthermore, we identified that X chromosome inactivation occurs in premeiotic spermatogonia. Overall, our results indicate: (i) transcription regulation in E. plorans spermatogenesis differs from the canonical pattern found in mammals and (ii) X chromosome inactivation is likely preceded by a process of heterochromatinization before the initiation of meiosis.

Tumorigenesis and cell competition in Drosophila in the absence of polyhomeotic function

Cell competition is a homeostatic process that eliminates by apoptosis unfit or undesirable cells from animal tissues, including tumor cells that appear during the life of the organism. In Drosophila there is evidence that many types of oncogenic cells are eliminated by cell competition. One exception is cells mutant for polyhomeotic (ph), a member of the Polycomb family of genes; most of the isolated mutant ph clones survive and develop tumorous overgrowths in imaginal discs. To characterize the tumorigenic effect of the lack of ph, we first studied the growth of different regions of the wing disc deficient in ph activity and found that the effect is restricted to the proximal appendage. Moreover, we found that ph-deficient tissue is partially refractory to apoptosis. Second, we analyzed the behavior of clones lacking ph function and found that many suffer cell competition but are not completely eliminated. Unexpectedly, we found that nonmutant cells also undergo cell competition when surrounded by ph-deficient cells, indicating that within the same tissue cell competition may operate in opposite directions. We suggest two reasons for the incompleteness of cell competition in ph mutant cells: 1) These cells are partially refractory to apoptosis, and 2) the loss of ph function alters the identity of imaginal cells and subsequently their cell affinities. It compromises the winner/loser interaction, a prerequisite for cell competition.

dRTEL1 is essential for the maintenance of Drosophila male germline stem cells

Stem cells have the potential to maintain undifferentiated state and differentiate into specialized cell types. Despite numerous progress has been achieved in understanding stem cell self-renewal and differentiation, many fundamental questions remain unanswered. In this study, we identify dRTEL1, the Drosophila homolog of Regulator of Telomere Elongation Helicase 1, as a novel regulator of male germline stem cells (GSCs). Our genome-wide transcriptome analysis and ChIP-Seq results suggest that dRTEL1 affects a set of candidate genes required for GSC maintenance, likely independent of its role in DNA repair. Furthermore, dRTEL1 prevents DNA damage-induced checkpoint activation in GSCs. Finally, dRTEL1 functions to sustain Stat92E protein levels, the key player in GSC maintenance. Together, our findings reveal an intrinsic role of the DNA helicase dRTEL1 in maintaining male GSC and provide insight into the function of dRTEL1.

Human Hazard Assessment Using Drosophila Wing Spot Test as an Alternative In Vivo Model for Genotoxicity Testing-A Review

Genomic instability, one of cancer's hallmarks, is induced by genotoxins from endogenous and exogenous sources, including reactive oxygen species (ROS), diet, and environmental pollutants. A sensitive in vivo genotoxicity test is required for the identification of human hazards to reduce the potential health risk. The somatic mutation and recombination test (SMART) or wing spot test is a genotoxicity assay involving Drosophila melanogaster (fruit fly) as a classical, alternative human model. This review describes the principle of the SMART assay in conjunction with its advantages and disadvantages and discusses applications of the assay covering all segments of health-related industries, including food, dietary supplements, drug industries, pesticides, and herbicides, as well as nanoparticles. Chemopreventive strategies are outlined as a global health trend for the anti-genotoxicity of interesting herbal extract compounds determined by SMART assay. The successful application of Drosophila for high-throughput screening of mutagens is also discussed as a future perspective.

Modeling Notch-Induced Tumor Cell Survival in the Drosophila Ovary Identifies Cellular and Transcriptional Response to Nuclear NICD Accumulation

Notch is a conserved developmental signaling pathway that is dysregulated in many cancer types, most often through constitutive activation. Tumor cells with nuclear accumulation of the active Notch receptor, NICD, generally exhibit enhanced survival while patients experience poorer outcomes. To understand the impact of NICD accumulation during tumorigenesis, we developed a tumor model using the Drosophila ovarian follicular epithelium. Using this system we demonstrated that NICD accumulation contributed to larger tumor growth, reduced apoptosis, increased nuclear size, and fewer incidents of DNA damage without altering ploidy. Using bulk RNA sequencing we identified key genes involved in both a pre- and post- tumor response to NICD accumulation. Among these are genes involved in regulating double-strand break repair, chromosome organization, metabolism, like raptor, which we experimentally validated contributes to early Notch-induced tumor growth. Finally, using single-cell RNA sequencing we identified follicle cell-specific targets in NICD-overexpressing cells which contribute to DNA repair and negative regulation of apoptosis. This valuable tumor model for nuclear NICD accumulation in adult Drosophila follicle cells has allowed us to better understand the specific contribution of nuclear NICD accumulation to cell survival in tumorigenesis and tumor progression.

Su(Hw) primes 66D and 7F Drosophila chorion genes loci for amplification through chromatin decondensation

Suppressor of Hairy wing [Su(Hw)] is an insulator protein that participates in regulating chromatin architecture and gene repression in Drosophila. In previous studies we have shown that Su(Hw) is also required for pre-replication complex (pre-RC) recruitment on Su(Hw)-bound sites (SBSs) in Drosophila S2 cells and pupa. Here, we describe the effect of Su(Hw) on developmentally regulated amplification of 66D and 7F Drosophila amplicons in follicle cells (DAFCs), widely used as models in replication studies. We show Su(Hw) binding co-localizes with all known DAFCs in Drosophila ovaries, whereas disruption of Su(Hw) binding to 66D and 7F DAFCs causes a two-fold decrease in the amplification of these loci. The complete loss of Su(Hw) binding to chromatin impairs pre-RC recruitment to all amplification regulatory regions of 66D and 7F loci at early oogenesis (prior to DAFCs amplification). These changes coincide with a considerable Su(Hw)-dependent condensation of chromatin at 66D and 7F loci. Although we observed the Brm, ISWI, Mi-2, and CHD1 chromatin remodelers at SBSs genome wide, their remodeler activity does not appear to be responsible for chromatin decondensation at the 66D and 7F amplification regulatory regions. We have discovered that, in addition to the CBP/Nejire and Chameau histone acetyltransferases, the Gcn5 acetyltransferase binds to 66D and 7F DAFCs at SBSs and this binding is dependent on Su(Hw). We propose that the main function of Su(Hw) in developmental amplification of 66D and 7F DAFCs is to establish a chromatin structure that is permissive to pre-RC recruitment.

DNase II mediates a parthanatos-like developmental cell death pathway in Drosophila primordial germ cells

During Drosophila embryonic development, cell death eliminates 30% of the primordial germ cells (PGCs). Inhibiting apoptosis does not prevent PGC death, suggesting a divergence from the conventional apoptotic program. Here, we demonstrate that PGCs normally activate an intrinsic alternative cell death (ACD) pathway mediated by DNase II release from lysosomes, leading to nuclear translocation and subsequent DNA double-strand breaks (DSBs). DSBs activate the DNA damage-sensing enzyme, Poly(ADP-ribose) (PAR) polymerase-1 (PARP-1) and the ATR/Chk1 branch of the DNA damage response. PARP-1 and DNase II engage in a positive feedback amplification loop mediated by the release of PAR polymers from the nucleus and the nuclear accumulation of DNase II in an AIF- and CypA-dependent manner, ultimately resulting in PGC death. Given the anatomical and molecular similarities with an ACD pathway called parthanatos, these findings reveal a parthanatos-like cell death pathway active during Drosophila development.

Cooperation between oncogenic Ras and wild-type p53 stimulates STAT non-cell autonomously to promote tumor radioresistance

Oncogenic RAS mutations are associated with tumor resistance to radiation therapy. Cell-cell interactions in the tumor microenvironment (TME) profoundly influence therapy outcomes. However, the nature of these interactions and their role in Ras tumor radioresistance remain unclear. Here we use Drosophila oncogenic Ras tissues and human Ras cancer cell radiation models to address these questions. We discover that cellular response to genotoxic stress cooperates with oncogenic Ras to activate JAK/STAT non-cell autonomously in the TME. Specifically, p53 is heterogeneously activated in Ras tumor tissues in response to irradiation. This mosaicism allows high p53-expressing Ras clones to stimulate JAK/STAT cytokines, which activate JAK/STAT in the nearby low p53-expressing surviving Ras clones, leading to robust tumor re-establishment. Blocking any part of this cell-cell communication loop re-sensitizes Ras tumor cells to irradiation. These findings suggest that coupling STAT inhibitors to radiotherapy might improve clinical outcomes for Ras cancer patients.

Phosphorylation of the Canonical Histone H2A Marks Foci of Damaged DNA in Malaria Parasites

Plasmodium falciparum is the deadliest human parasite that causes malaria when it reaches the bloodstream and begins proliferating inside red blood cells, where the parasites are particularly prone to DNA damage. The molecular mechanisms that allow these pathogens to maintain their genome integrity under such conditions are also the driving force for acquiring genome plasticity that enables them to create antigenic variation and become resistant to essentially all available drugs.

Plasmodium falciparum parasites proliferate within circulating red blood cells and are responsible for the deadliest form of human malaria. These parasites are exposed to numerous intrinsic and external sources that could cause DNA damage; therefore, they have evolved efficient mechanisms to protect their genome integrity and allow them to proliferate under such conditions. In higher eukaryotes, double-strand breaks rapidly lead to phosphorylation of the core histone variant H2A.X, which marks the site of damaged DNA. We show that in P. falciparum that lacks the H2A.X variant, the canonical P. falciparum H2A (PfH2A) is phosphorylated on serine 121 upon exposure to sources of DNA damage. We further demonstrate that phosphorylated PfH2A is recruited to foci of damaged chromatin shortly after exposure to sources of damage, while the nonphosphorylated PfH2A remains spread throughout the nucleoplasm. In addition, we found that PfH2A phosphorylation is dynamic and that over time, as the parasite activates the repair machinery, this phosphorylation is removed. Finally, we demonstrate that these phosphorylation dynamics could be used to establish a novel and direct DNA repair assay in P. falciparum.

IMPORTANCEPlasmodium falciparum is the deadliest human parasite that causes malaria when it reaches the bloodstream and begins proliferating inside red blood cells, where the parasites are particularly prone to DNA damage. The molecular mechanisms that allow these pathogens to maintain their genome integrity under such conditions are also the driving force for acquiring genome plasticity that enables them to create antigenic variation and become resistant to essentially all available drugs. However, mechanisms of DNA damage response and repair have not been extensively studied for these parasites. The paper addresses our recent discovery that P. falciparum that lacks the histone variant H2A.X phosphorylates its canonical core histone PfH2A in response to exposure to DNA damage. The process of DNA repair in Plasmodium was mostly studied indirectly. Our findings enabled us to establish a direct DNA repair assay for P. falciparum similar to assays that are widely used in model organisms.

Live Cell Imaging of Nuclear Actin Filaments and Heterochromatic Repair foci in Drosophila and Mouse Cells

Pericentromeric heterochromatin is mostly composed of repeated DNA sequences, which are prone to aberrant recombination during double-strand break (DSB) repair. Studies in Drosophila and mouse cells revealed that 'safe' homologous recombination (HR) repair of these sequences relies on the relocalization of repair sites to outside the heterochromatin domain before Rad51 recruitment. Relocalization requires a striking network of nuclear actin filaments (F-actin) and myosins that drive directed motions. Understanding this pathway requires the detection of nuclear actin filaments that are significantly less abundant than those in the cytoplasm, and the imaging and tracking of repair sites for long time periods. Here, we describe an optimized protocol for live cell imaging of nuclear F-actin in Drosophila cells, and for repair focus tracking in mouse cells, including: imaging setup, image processing approaches, and analysis methods. We emphasize approaches that can be applied to identify the most effective fluorescent markers for live cell imaging, strategies to minimize photobleaching and phototoxicity with a DeltaVision deconvolution microscope, and image processing and analysis methods using SoftWoRx and Imaris software. These approaches enable a deeper understanding of the spatial and temporal dynamics of heterochromatin repair and have broad applicability in the fields of nuclear architecture, nuclear dynamics, and DNA repair.

spn-A/rad51 mutant exhibits enhanced genomic damage, cell death and low temperature sensitivity in somatic tissues

Homologous recombination (HR) is one of the key pathways to repair double-strand breaks (DSBs). Rad51 serves an important function of catalysing strand exchange between two homologous sequences in the HR pathway. In higher organisms, rad51 function is indispensable with its absence leading to early embryonic lethality, thus precluding any mechanistic probing of the system. In contrast, the absence of Drosophila rad51 (spn-A/rad51) has been associated with defects in the germline, without any reported detrimental consequences to Drosophila somatic tissues. In this study, we have performed a systematic analysis of developmental defects in somatic tissues of spn-A mutant flies by using genetic complementation between multiple spn-A alleles. Our current study, for the first time, uncovers a requirement for spn-A in somatic tissue maintenance during both larval and pupal stages. Also, we show that spn-A mutant exhibits patterning defects in abdominal cuticle in the stripes and bristles, while there appear to be only subtle defects in the adult wing and eye. Interestingly, spn-A mutant shows a discernible phenotype of low temperature sensitivity, suggesting a role of spn-A in temperature sensitive cellular processes. In summary, our study describes the important role played by spn-A/rad51 in Drosophila somatic tissues.

Loss of the spectraplakin gene Short stop induces a DNA damage response in Drosophila epithelia

Epithelia are an eminent tissue type and a common driver of tumorigenesis, requiring continual precision in cell division to maintain tissue structure and genome integrity. Mitotic defects often trigger apoptosis, impairing cell viability as a tradeoff for tumor suppression. Identifying conditions that lead to cell death and understanding the mechanisms behind this response are therefore of considerable importance. Here we investigated how epithelia of the Drosophila wing disc respond to loss of Short stop (Shot), a cytoskeletal crosslinking spectraplakin protein that we previously found to control mitotic spindle assembly and chromosome dynamics. In contrast to other known spindle-regulating genes, Shot knockdown induces apoptosis in the absence of Jun kinase (JNK) activation, but instead leads to elevated levels of active p38 kinase. Shot loss leads to double-strand break (DSB) DNA damage, and the apoptotic response is exacerbated by concomitant loss of p53. DSB accumulation is increased by suppression of the spindle assembly checkpoint, suggesting this effect results from chromosome damage during error-prone mitoses. Consistent with DSB induction, we found that the DNA damage and stress response genes, Growth arrest and DNA damage (GADD45) and Apoptosis signal-regulating kinase 1 (Ask1), are transcriptionally upregulated as part of the shot-induced apoptotic response. Finally, co-depletion of Shot and GADD45 induced significantly higher rates of chromosome segregation errors in cultured cells and suppressed shot-induced mitotic arrest. Our results demonstrate that epithelia are capable of mounting molecularly distinct responses to loss of different spindle-associated genes and underscore the importance of proper cytoskeletal organization in tissue homeostasis.

Musashi expression in intestinal stem cells attenuates radiation-induced decline in intestinal permeability and survival in Drosophila

Exposure to genotoxic stress by environmental agents or treatments, such as radiation therapy, can diminish healthspan and accelerate aging. We have developed a Drosophila melanogaster model to study the molecular effects of radiation-induced damage and repair. Utilizing a quantitative intestinal permeability assay, we performed an unbiased GWAS screen (using 156 strains from the Drosophila Genetic Reference Panel) to search for natural genetic variants that regulate radiation-induced gut permeability in adult D. melanogaster. From this screen, we identified an RNA binding protein, Musashi (msi), as one of the possible genes associated with changes in intestinal permeability upon radiation. The overexpression of msi promoted intestinal stem cell proliferation, which increased survival after irradiation and rescued radiation-induced intestinal permeability. In summary, we have established D. melanogaster as an expedient model system to study the effects of radiation-induced damage to the intestine in adults and have identified msi as a potential therapeutic target.

BCAS2, a protein enriched in advanced prostate cancer, interacts with NBS1 to enhance DNA double-strand break repair

Background

Breast cancer amplified sequence 2 (BCAS2) plays crucial roles in pre-mRNA splicing and androgen receptor transcription. Previous studies suggested that BCAS2 is involved in double-strand breaks (DSB); therefore, we aimed to characterise its mechanism and role in prostate cancer (PCa).

Methods

Western blotting and immunofluorescence microscopy were used to assay the roles of BCAS2 in the DSBs of PCa cells and apoptosis in Drosophila, respectively. The effect of BCAS2 dosage on non-homologous end joining (NHEJ) and homologous recombination (HR) were assayed by precise end-joining assay and flow cytometry, respectively. Glutathione-S-transferase pulldown and co-immunoprecipitation assays were used to determine whether and how BCAS2 interacts with NBS1. The expression of BCAS2 and other proteins in human PCa was determined by immunohistochemistry.

Results

BCAS2 helped repair radiation-induced DSBs efficiently in both human PCa cells and Drosophila. BCAS2 enhanced both NHEJ and HR, possibly by interacting with NBS1, which involved the BCAS2 N-terminus as well as both the NBS1 N- and C-termini. The overexpression of BCAS2 was significantly associated with higher Gleason and pathology grades and shorter survival in patients with PCa.

Conclusion

BCAS2 promotes two DSB repair pathways by interacting with NBS1, and it may affect PCa progression.

Targeted De Novo Centromere Formation in Drosophila Reveals Plasticity and Maintenance Potential of CENP-A Chromatin

Centromeres are essential for accurate chromosome segregation and are marked by centromere protein A (CENP-A) nucleosomes. Mis-targeted CENP-A chromatin has been shown to seed centromeres at non-centromeric DNA. However, the requirements for such de novo centromere formation and transmission in vivo remain unknown. Here, we employ Drosophila melanogaster and the LacI/lacO system to investigate the ability of targeted de novo centromeres to assemble and be inherited through development. De novo centromeres form efficiently at six distinct genomic locations, which include actively transcribed chromatin and heterochromatin, and cause widespread chromosomal instability. During tethering, de novo centromeres sometimes prevail, causing the loss of the endogenous centromere via DNA breaks and HP1-dependent epigenetic inactivation. Transient induction of de novo centromeres and chromosome healing in early embryogenesis show that, once established, these centromeres can be maintained through development. Our results underpin the ability of CENP-A chromatin to establish and sustain mitotic centromere function in Drosophila.

Piwi reduction in the aged niche eliminates germline stem cells via Toll-GSK3 signaling

Transposons are known to participate in tissue aging, but their effects on aged stem cells remain unclear. Here, we report that in the Drosophila ovarian germline stem cell (GSC) niche, aging-related reductions in expression of Piwi (a transposon silencer) derepress retrotransposons and cause GSC loss. Suppression of Piwi expression in the young niche mimics the aged niche, causing retrotransposon depression and coincident activation of Toll-mediated signaling, which promotes Glycogen synthase kinase 3 activity to degrade β-catenin. Disruption of β-catenin-E-cadherin-mediated GSC anchorage then results in GSC loss. Knocking down gypsy (a highly active retrotransposon) or toll, or inhibiting reverse transcription in the piwi-deficient niche, suppresses GSK3 activity and β-catenin degradation, restoring GSC-niche attachment. This retrotransposon-mediated impairment of aged stem cell maintenance may have relevance in many tissues, and could represent a viable therapeutic target for aging-related tissue degeneration.

Sleep Loss Can Cause Death through Accumulation of Reactive Oxygen Species in the Gut

The view that sleep is essential for survival is supported by the ubiquity of this behavior, the apparent existence of sleep-like states in the earliest animals, and the fact that severe sleep loss can be lethal. The cause of this lethality is unknown. Here we show, using flies and mice, that sleep deprivation leads to accumulation of reactive oxygen species (ROS) and consequent oxidative stress, specifically in the gut. ROS are not just correlates of sleep deprivation but drivers of death: their neutralization prevents oxidative stress and allows flies to have a normal lifespan with little to no sleep. The rescue can be achieved with oral antioxidant compounds or with gut-targeted transgenic expression of antioxidant enzymes. We conclude that death upon severe sleep restriction can be caused by oxidative stress, that the gut is central in this process, and that survival without sleep is possible when ROS accumulation is prevented. VIDEO ABSTRACT.

Sertraline induces DNA damage and cellular toxicity in Drosophila that can be ameliorated by antioxidants

Sertraline hydrochloride is a commonly prescribed antidepressant medication that acts by amplifying serotonin signaling. Numerous studies have suggested that children of women  taking sertraline during pregnancy have an increased risk of developmental defects. Resolving the degree of risk for human fetuses requires comprehensive knowledge of the pathways affected by this drug. We utilized a Drosophila melanogaster model system to assess the effects of sertraline throughout development. Ingestion of sertraline by females did not affect their fecundity or embryogenesis in their progeny. However, larvae that consumed sertraline experienced delayed developmental progression and reduced survival at all stages of development. Genetic experiments showed that these effects were mostly independent of aberrant extracellular serotonin levels. Using an ex vivo imaginal disc culture system, we showed that mitotically active sertraline-treated tissues accumulate DNA double-strand breaks and undergo apoptosis at increased frequencies. Remarkably, the sertraline-induced genotoxicity was partially rescued by co-incubation with ascorbic acid, suggesting that sertraline induces oxidative DNA damage. These findings may have implications for the biomedicine of sertraline-induced birth defects.

Special vulnerability of somatic niche cells to transposable element activation in Drosophila larval ovaries

In the Drosophila ovary, somatic escort cells (ECs) form a niche that promotes differentiation of germline stem cell (GSC) progeny. The piRNA (Piwi-interacting RNA) pathway, which represses transposable elements (TEs), is required in ECs to prevent the accumulation of undifferentiated germ cells (germline tumor phenotype). The soma-specific piRNA cluster flamenco (flam) produces a substantial part of somatic piRNAs. Here, we characterized the biological effects of somatic TE activation on germ cell differentiation in flam mutants. We revealed that the choice between normal and tumorous phenotypes of flam mutant ovaries depends on the number of persisting ECs, which is determined at the larval stage. Accordingly, we found much more frequent DNA breaks in somatic cells of flam larval ovaries than in adult ECs. The absence of Chk2 or ATM checkpoint kinases dramatically enhanced oogenesis defects of flam mutants, in contrast to the germline TE-induced defects that are known to be mostly suppressed by сhk2 mutation. These results demonstrate a crucial role of checkpoint kinases in protecting niche cells against deleterious TE activation and suggest substantial differences between DNA damage responses in ovarian somatic and germ cells.

DNA damage response and repair in perspective: Aedes aegypti, Drosophila melanogaster and Homo sapiens

Background

The maintenance of genomic integrity is the responsibility of a complex network, denominated the DNA damage response (DDR), which controls the lesion detection and DNA repair. The main repair pathways are base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), homologous recombination repair (HR) and non-homologous end joining repair (NHEJ). They correct double-strand breaks (DSB), single-strand breaks, mismatches and others, or when the damage is quite extensive and repair insufficient, apoptosis is activated.

Methods

In this study we used the BLAST reciprocal best-hit methodology to search for DDR orthologs proteins in Aedes aegypti. We also provided a comparison between Ae. aegypti, D. melanogaster and human DDR network.

Results

Our analysis revealed the presence of ATR and ATM signaling, including the H2AX ortholog, in Ae. aegypti. Key DDR proteins (orthologs to RAD51, Ku and MRN complexes, XP-components, MutS and MutL) were also identified in this insect. Other proteins were not identified in both Ae. aegypti and D. melanogaster, including BRCA1 and its partners from BRCA1-A complex, TP53BP1, PALB2, POLk, CSA, CSB and POLβ. In humans, their absence affects DSB signaling, HR and sub-pathways of NER and BER. Seven orthologs not known in D. melanogaster were found in Ae. aegypti (RNF168, RIF1, WRN, RAD54B, RMI1, DNAPKcs, ARTEMIS).

Conclusions

The presence of key DDR proteins in Ae. aegypti suggests that the main DDR pathways are functional in this insect, and the identification of proteins not known in D. melanogaster can help fill gaps in the DDR network. The mapping of the DDR network in Ae. aegypti can support mosquito biology studies and inform genetic manipulation approaches applied to this vector.