RESUMO
Viable yet damaged cells can accumulate during development and aging. Although eliminating those cells may benefit organ function, identification of this less fit cell population remains challenging. Previously, we identified a molecular mechanism, based on "fitness fingerprints" displayed on cell membranes, which allows direct fitness comparison among cells in Drosophila. Here, we study the physiological consequences of efficient cell selection for the whole organism. We find that fitness-based cell culling is naturally used to maintain tissue health, delay aging, and extend lifespan in Drosophila. We identify a gene, azot, which ensures the elimination of less fit cells. Lack of azot increases morphological malformations and susceptibility to random mutations and accelerates tissue degeneration. On the contrary, improving the efficiency of cell selection is beneficial for tissue health and extends lifespan.
Assuntos
Proteínas de Ligação ao Cálcio/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/fisiologia , Envelhecimento , Sequência de Aminoácidos , Animais , Proteínas de Ligação ao Cálcio/química , Proteínas de Ligação ao Cálcio/genética , Proteínas de Drosophila/química , Proteínas de Drosophila/genética , Drosophila melanogaster/citologia , Drosophila melanogaster/crescimento & desenvolvimento , Longevidade , Dados de Sequência Molecular , Neurônios/citologia , Neurônios/metabolismo , Regiões Promotoras Genéticas , Alinhamento de SequênciaRESUMO
In humans, the adaptive immune system uses the exchange of information between cells to detect and eliminate foreign or damaged cells; however, the removal of unwanted cells does not always require an adaptive immune system1,2. For example, cell selection in Drosophila uses a cell selection mechanism based on 'fitness fingerprints', which allow it to delay ageing3, prevent developmental malformations3,4 and replace old tissues during regeneration5. At the molecular level, these fitness fingerprints consist of combinations of Flower membrane proteins3,4,6. Proteins that indicate reduced fitness are called Flower-Lose, because they are expressed in cells marked to be eliminated6. However, the presence of Flower-Lose isoforms at a cell's membrane does not always lead to elimination, because if neighbouring cells have similar levels of Lose proteins, the cell will not be killed4,6,7. Humans could benefit from the capability to recognize unfit cells, because accumulation of damaged but viable cells during development and ageing causes organ dysfunction and disease8-17. However, in Drosophila this mechanism is hijacked by premalignant cells to gain a competitive growth advantage18. This would be undesirable for humans because it might make tumours more aggressive19-21. It is unknown whether a similar mechanism of cell-fitness comparison is present in humans. Here we show that two human Flower isoforms (hFWE1 and hFWE3) behave as Flower-Lose proteins, whereas the other two isoforms (hFWE2 and hFWE4) behave as Flower-Win proteins. The latter give cells a competitive advantage over cells expressing Lose isoforms, but Lose-expressing cells are not eliminated if their neighbours express similar levels of Lose isoforms; these proteins therefore act as fitness fingerprints. Moreover, human cancer cells show increased Win isoform expression and proliferate in the presence of Lose-expressing stroma, which confers a competitive growth advantage on the cancer cells. Inhibition of the expression of Flower proteins reduces tumour growth and metastasis, and induces sensitivity to chemotherapy. Our results show that ancient mechanisms of cell recognition and selection are active in humans and affect oncogenic growth.
Assuntos
Canais de Cálcio/metabolismo , Proliferação de Células , Proteínas de Drosophila/metabolismo , Neoplasias/patologia , Isoformas de Proteínas/metabolismo , Animais , Canais de Cálcio/genética , Linhagem Celular Tumoral , Transformação Celular Neoplásica/genética , Drosophila melanogaster , Feminino , Técnicas de Silenciamento de Genes , Humanos , Masculino , Metástase Neoplásica , Neoplasias/tratamento farmacológico , Isoformas de Proteínas/genéticaRESUMO
In this selection, we celebrate the art of science by highlighting some of the submitted cover images from the past year. In this collection, our authors share the stories behind their inspiration for how to portray their science to captivate a broader audience.
RESUMO
Recruitment of stem cells is crucial for tissue repair. Although stem cell niches can provide important signals, little is known about mechanisms that coordinate the engagement of disseminated stem cells across an injured tissue. In Drosophila, adult brain lesions trigger local recruitment of scattered dormant neural stem cells suggesting a mechanism for creating a transient stem cell activation zone. Here, we find that injury triggers a coordinated response in neuro-glial clusters that promotes the spread of a neuron-derived stem cell factor via glial secretion of the lipocalin-like transporter Swim. Strikingly, swim is induced in a Hif1-α-dependent manner in response to brain hypoxia. Mammalian Swim (Lcn7) is also upregulated in glia of the mouse hippocampus upon brain injury. Our results identify a central role of neuro-glial clusters in promoting neural stem cell activation at a distance, suggesting a conserved function of the HIF1-α/Swim/Wnt module in connecting injury-sensing and regenerative outcomes.
Assuntos
Drosophila , Células-Tronco Neurais , Animais , Mamíferos , Camundongos , Neuroglia , Neurônios , Nicho de Células-TroncoRESUMO
Cancer is the result of sequential genetic changes over time that transform a cell into a malignant and ultimately invasive entity. The insight that cancerous cells arise from a series of mutations in oncogenes and tumor suppressors, commonly known as multistep carcinogenesis, has been conceptually elaborated and proven in the last 20 years. Although knowledge about late steps of cancerogenesis and disease progression has greatly advanced, the initial molecular events remain largely unknown. Basic research in Drosophila has started the quest to find early markers that detect initial clonal expansion of precancerous cells. These efforts were spurred by novel findings demonstrating that certain mutations transform cells into super-competitors that expand at the expense of the surrounding epithelial cells without inducing histological changes. This mechanism, discovered as super competition in the fly, might also lie at the heart of a clinical observation termed 'field cancerization'. This review aims to bring together current understanding from basic research on cell competition and clinical studies that have analyzed field characteristics to highlight parallels and possible connections.
Assuntos
Transformação Celular Neoplásica/genética , Lesões Pré-Cancerosas/genética , Animais , Apoptose , Carcinoma de Células Escamosas/genética , Carcinoma de Células Escamosas/patologia , Divisão Celular , Ciclina D1/genética , Drosophila/genética , Genes Supressores de Tumor , Marcadores Genéticos , Neoplasias de Cabeça e Pescoço/genética , Neoplasias de Cabeça e Pescoço/patologia , Humanos , Perda de Heterozigosidade , Modelos Biológicos , Neoplasias/genética , Neoplasias/patologia , Oncogenes , Lesões Pré-Cancerosas/diagnóstico , Lesões Pré-Cancerosas/patologiaRESUMO
The use of adult Drosophila melanogaster as a model for hematopoiesis or organismal immunity has been debated. Addressing this question, we identify an extensive reservoir of blood cells (hemocytes) at the respiratory epithelia (tracheal air sacs) of the thorax and head. Lineage tracing and functional analyses demonstrate that the majority of adult hemocytes are phagocytic macrophages (plasmatocytes) from the embryonic lineage that parallels vertebrate tissue macrophages. Surprisingly, we find no sign of adult hemocyte expansion. Instead, hemocytes play a role in relaying an innate immune response to the blood cell reservoir: through Imd signaling and the Jak/Stat pathway ligand Upd3, hemocytes act as sentinels of bacterial infection, inducing expression of the antimicrobial peptide Drosocin in respiratory epithelia and colocalizing fat body domains. Drosocin expression in turn promotes animal survival after infection. Our work identifies a multi-signal relay of organismal humoral immunity, establishing adult Drosophila as model for inter-organ immunity.
Assuntos
Células Sanguíneas/metabolismo , Hematopoese/fisiologia , Macrófagos/metabolismo , Mucosa Respiratória/metabolismo , Animais , Drosophila/metabolismo , Hemócitos/metabolismo , Imunidade Celular/imunologia , Imunidade Inata/imunologia , Janus Quinases/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Adult stem cells in mammals are important for normal tissue renewal (homeostasis) and regeneration after injury. In the past ten years, different types of homeostatic adult stem cells have also been identified in the genetically accessible fruit fly (Drosophila melanogaster), among which intestinal stem cells have taken centre stage. Recent studies provide evidence that adult fly tissues may also harbor quiescent stem cells, which can enter cell cycle upon injury to regenerate compromised tissue. Such damage-responsive stem cells have been described in flight muscles, the adult brain and in a narrow region of the fly hindgut. Strikingly, many mammalian tissues have also been shown to maintain quiescent, but regeneration-competent, stem cells. However, little is known about the injury-induced signals that lead to their activation. Here, we provide a brief overview of active and damage-responsive adult stem cells in the fruit fly and focus on injury-dependent signalling events. We highlight the potential of Drosophila to model damage-induced stem cell activation to deepen our molecular understanding of how dormant stem cells can be efficiently recruited for tissue repair after injury.
Assuntos
Drosophila melanogaster/fisiologia , Homeostase/fisiologia , Intestinos/fisiologia , Regeneração/fisiologia , Células-Tronco/fisiologia , Animais , Ciclo Celular/fisiologia , Diferenciação Celular/fisiologia , Proliferação de Células/fisiologia , Drosophila melanogaster/citologia , Intestinos/citologia , Transdução de Sinais/fisiologia , Células-Tronco/citologiaRESUMO
Alzheimer's disease (AD) is the most common form of dementia, impairing cognitive and motor functions. One of the pathological hallmarks of AD is neuronal loss, which is not reflected in mouse models of AD. Therefore, the role of neuronal death is still uncertain. Here, we used a Drosophila AD model expressing a secreted form of human amyloid-ß42 peptide and showed that it recapitulates key aspects of AD pathology, including neuronal death and impaired long-term memory. We found that neuronal apoptosis is mediated by cell fitness-driven neuronal culling, which selectively eliminates impaired neurons from brain circuits. We demonstrated that removal of less fit neurons delays ß-amyloid-induced brain damage and protects against cognitive and motor decline, suggesting that contrary to common knowledge, neuronal death may have a beneficial effect in AD.
Assuntos
Peptídeos beta-Amiloides/toxicidade , Encéfalo/patologia , Encéfalo/fisiopatologia , Transtornos Cognitivos/patologia , Transtornos Cognitivos/fisiopatologia , Atividade Motora , Neurônios/patologia , Neuroproteção , Fragmentos de Peptídeos/toxicidade , Animais , Encéfalo/efeitos dos fármacos , Morte Celular , Corte , Modelos Animais de Doenças , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Epitélio/efeitos dos fármacos , Epitélio/metabolismo , Epitélio/patologia , Feminino , Humanos , Doença de Huntington/patologia , Longevidade , Masculino , Memória de Longo Prazo/efeitos dos fármacos , Atividade Motora/efeitos dos fármacos , Proteínas Mutantes/metabolismo , Neurônios/efeitos dos fármacos , Neuroproteção/efeitos dos fármacos , Doença de Parkinson/patologia , Vacúolos/metabolismoRESUMO
During brain development, highly complex and interconnected neural circuits are established. This intricate wiring needs to be robust to faithfully perform adult brain function throughout life, but at the same time offer room for plasticity to integrate new information. In the mammalian brain, adult-born neurons are produced in restricted niches harboring neural stem cells. In the fruit fly Drosophila, low-level adult neurogenesis arising from a dispersed population of neural progenitors has recently been detected in the optic lobes. Strikingly, these normally quiescent neural stem cells proliferate upon brain injury and produce new neurons for brain regeneration. Here, we review adult neurogenesis in crustaceans and insects and highlight that neurogenesis in the visual system is prominent in arthropods, but its role and underlying mechanisms are unclear. Moreover, we discuss how the study of damage-responsive progenitor cells in Drosophila may help to understand robust regenerative neurogenesis and open new avenues to enhance brain repair after injury or stroke in humans.
RESUMO
Attractive and repulsive signals guide migrating nerve cells in all directions when the nervous system starts to form. The neurons extend thin processes, axons, that connect over wide distances with other brain cells to form a complicated neuronal network. One of the most fascinating questions in neuroscience is how the correct wiring of billions of nerve cells in our brain is controlled. Several protein families are known to serve as guidance cues for navigating neurons and axons. Nevertheless, the combinatorial potential of these proteins seems to be insufficient to sculpt the entire neuronal network and the appropriate formation of connections. Recently, heparan sulfate proteoglycans (HSPGs), which are present on the cell surface of neurons and in the extracellular matrix through which neurons and axons migrate, have been found to play a role in regulating cell migration and axon guidance. Intriguingly, the large number of distinct modifications that can be put onto the sugar side chains of these PGs would in principle allow for an enormous diversity of HSPGs, which could help in regulating the vast number of guidance choices taken by individual neurons. In this review, we will focus on the role of the cell surface HSPGs syndecan and glypican and specific HS modifications in promoting neuronal migration, axon guidance, and synapse formation.
Assuntos
Movimento Celular , Glipicanas/metabolismo , Neurônios/citologia , Neurônios/metabolismo , Transdução de Sinais , Sindecanas/metabolismo , Animais , Proteoglicanas de Heparan Sulfato/metabolismo , HumanosRESUMO
Neuronal circuits in the adult brain have long been viewed as static and stable. However, research in the past 20 years has shown that specialized regions of the adult brain, which harbor adult neural stem cells, continue to produce new neurons in a wide range of species. Brain plasticity is also observed after injury. Depending on the extent and permissive environment of neurogenic regions, different organisms show great variability in their capacity to replace lost neurons by endogenous neurogenesis. In Zebrafish and Drosophila, the formation of new neurons from progenitor cells in the adult brain was only discovered recently. Here, we compare properties of adult neural stem cells, their niches and regenerative responses from mammals to flies. Current models of brain injury have revealed that specific injury-induced genetic programs and comparison of neuronal fitness are implicated in brain repair. We highlight the potential of these recently implemented models of brain regeneration to identify novel regulators of stem cell activation and regenerative neurogenesis.
Assuntos
Lesões Encefálicas/fisiopatologia , Modelos Genéticos , Neurogênese/genética , Neurônios/fisiologia , Regeneração/genética , Animais , HumanosRESUMO
Darwinian-like cell selection has been studied during development and cancer [1-11]. Cell selection is often mediated by direct intercellular comparison of cell fitness, using "fitness fingerprints" [12-14]. In Drosophila, cells compare their fitness via several isoforms of the transmembrane protein Flower [12, 13]. Here, we studied the role of intercellular fitness comparisons during regeneration. Regeneration-competent organisms are traditionally injured by amputation [15, 16], whereas in clinically relevant injuries such as local ischemia or traumatic injury, damaged tissue remains within the organ [17-19]. We reasoned that "Darwinian" interactions between old and newly formed tissues may be important in the elimination of damaged cells. We used a model of adult brain regeneration in Drosophila in which mechanical puncture activates regenerative neurogenesis based on damage-responsive stem cells [20]. We found that apoptosis after brain injury occurs in damage-exposed tissue located adjacent to zones of de novo neurogenesis. Injury-affected neurons start to express isoforms of the Flower cell fitness indicator protein not found on intact neurons. We show that this change in the neuronal fitness fingerprint is required to recognize and eliminate such neurons. Moreover, apoptosis is inhibited if all neurons express "low-fitness" markers, showing that the availability of new and healthy cells drives tissue replacement. In summary, we found that elimination of impaired tissue during brain regeneration requires comparison of neuronal fitness and that tissue replacement after brain damage is coordinated by injury-modulated fitness fingerprints. Intercellular fitness comparisons between old and newly formed tissues could be a general mechanism of regenerative tissue replacement.
Assuntos
Lesões Encefálicas/fisiopatologia , Encéfalo/fisiopatologia , Aptidão Genética , Neurônios/metabolismo , Regeneração , Animais , Apoptose , Lesões Encefálicas/patologia , Drosophila , Neurônios/citologia , Neurônios/patologiaRESUMO
Metazoans have evolved ways to engage only the most appropriate cells for long-term tissue development and homeostasis. In many cases, competitive interactions have been shown to guide such cell selection events. In Drosophila, a process termed cell competition eliminates slow proliferating cells from growing epithelia. Recent studies show that cell competition is conserved in mammals with crucial functions like the elimination of suboptimal stem cells from the early embryo and the replacement of old T-cell progenitors in the thymus to prevent tumor formation. Moreover, new data in Drosophila has revealed that fitness indicator proteins, required for cell competition, are also involved in the culling of retinal neurons suggesting that 'fitness fingerprints' may play a general role in cell selection.
Assuntos
Fenômenos Fisiológicos Celulares , Envelhecimento/patologia , Envelhecimento/fisiologia , Animais , Proliferação de Células , Drosophila/citologia , Humanos , Mamíferos/fisiologia , Neoplasias/patologia , Células-Tronco/patologiaRESUMO
Adult neurogenesis has been linked to several cognitive functions and neurological disorders. Description of adult neurogenesis in a model organism like Drosophila could facilitate the genetic study of normal and abnormal neurogenesis in the adult brain. So far, formation of new neurons has not been detected in adult fly brains and hence has been thought to be absent in Drosophila. Here, we used an improved lineage-labeling method to show that, surprisingly, adult neurogenesis occurs in the medulla cortex of the Drosophila optic lobes. We also find that acute brain damage to this region stimulates adult neurogenesis. Finally, we identify a factor induced by acute damage, which is sufficient to specifically activate the proliferation of a cell type with adult neuroblast characteristics. Our results reveal unexpected plasticity in the adult Drosophila brain and describe a unique model for the genetic analysis of adult neurogenesis, plasticity, and brain regeneration.
Assuntos
Drosophila/crescimento & desenvolvimento , Animais , Encéfalo/citologia , Encéfalo/crescimento & desenvolvimento , Drosophila/metabolismo , Células-Tronco Neurais/citologia , NeurogêneseRESUMO
BACKGROUND: The flower gene has been previously linked to the elimination of slow dividing epithelial cells during development in a process known as "cell competition." During cell competition, different isoforms of the Flower protein are displayed at the cell membrane and reveal the reduced fitness of slow proliferating cells, which are therefore recognized, eliminated, and replaced by their normally dividing neighbors. This mechanism acts as a "cell quality" control in proliferating tissues. RESULTS: Here, we use the Drosophila eye as a model to study how unwanted neurons are culled during retina development and find that flower is required and sufficient for the recognition and elimination of supernumerary postmitotic neurons, contained within incomplete ommatidia units. This constitutes the first description of the "Flower Code" functioning as a cell selection mechanism in postmitotic cells and is also the first report of a physiological role for this cell quality control machinery. CONCLUSIONS: Our results show that the "Flower Code" is a general system to reveal cell fitness and that it may play similar roles in creating optimal neural networks in higher organisms. The Flower Code seems to be a more general mechanism for cell monitoring and selection than previously recognized.
Assuntos
Canais de Cálcio/genética , Proteínas de Drosophila/genética , Drosophila melanogaster/fisiologia , Regulação da Expressão Gênica no Desenvolvimento , Neurônios/fisiologia , Retina/crescimento & desenvolvimento , Animais , Canais de Cálcio/metabolismo , Morte Celular , Proliferação de Células , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Drosophila melanogaster/crescimento & desenvolvimento , Marcação In Situ das Extremidades Cortadas , Reação em Cadeia da Polimerase , Interferência de RNARESUMO
Heparan sulfate proteoglycans (HSPGs) are proteins with long covalently attached sugar side chains of the heparan sulfate (HS) type. Depending on the cellular context HS chains carry multiple structural modifications such as sulfate residues or epimerized sugars allowing them to bind to a wide range of molecules. HSPGs have been found to play extremely diverse roles in animal development and were shown to interact with certain axon guidance molecules. In this study we describe the role of the Caenorhabditis elegans HSPG core proteins Syndecan (SDN-1) and Glypican (LON-2) and the HS modifying enzymes in the dorsal guidance of D-type motor axons, a process controlled mainly by the conserved axon guidance molecule UNC-6/Netrin. Our genetic analysis established the specific HS code relevant for this axon guidance event. Using two sensitized genetic backgrounds, we isolated novel components influencing D-type motor axon guidance with a link to HSPGs, as well as new alleles of several previously characterized axon guidance genes. Interestingly, the dorsal axon guidance defects induced by mutations in zfp-1 or lin-35 depended on the transgene oxIs12 used to visualize the D-type motor neurons. oxIs12 is a large multi-copy transgene that enlarges the X chromosome by approximately 20%. In a search for genes with a comparable phenotype we found that a mutation in the known dosage compensation gene dpy-21 showed similar axon guidance defects as zfp-1 or lin-35 mutants. Thus, derepression of genes on X, where many genes relevant for HS dependent axon guidance are located, might also influence axon guidance of D-type motor neurons.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/citologia , Caenorhabditis elegans/metabolismo , Proteoglicanas de Heparan Sulfato/metabolismo , Heparitina Sulfato/metabolismo , Neurônios Motores/citologia , Proteínas do Tecido Nervoso/metabolismo , Animais , Neurônios Motores/metabolismo , NetrinasRESUMO
Skin papillomas arise as a result of clonal expansion of mutant cells. It has been proposed that the expansion of pretumoral cell clones is propelled not only by the increased proliferation capacity of mutant cells, but also by active cell selection. Previous studies in Drosophila describe a clonal selection process mediated by the Flower (Fwe) protein, whereby cells that express certain Fwe isoforms are recognized and forced to undergo apoptosis. It was further shown that knock down of fwe expression in Drosophila can prevent the clonal expansion of dMyc-overexpressing pretumoral cells. Here, we study the function of the single predicted mouse homolog of Drosophila Fwe, referred to as mFwe, by clonal overexpression of mFwe isoforms in Drosophila and by analyzing mFwe knock-out mice. We show that clonal overexpression of certain mFwe isoforms in Drosophila also triggers non-autonomous cell death, suggesting that Fwe function is evolutionarily conserved. Although mFwe-deficient mice display a normal phenotype, they develop a significantly lower number of skin papillomas upon exposure to DMBA/TPA two-stage skin carcinogenesis than do treated wild-type and mFwe heterozygous mice. Furthermore, mFwe expression is higher in papillomas and the papilloma-surrounding skin of treated wild-type mice compared with the skin of untreated wild-type mice. Thus, we propose that skin papilloma cells take advantage of mFwe activity to facilitate their clonal expansion.
Assuntos
Canais de Cálcio/deficiência , Transformação Celular Neoplásica/patologia , Suscetibilidade a Doenças/patologia , Papiloma/patologia , Neoplasias Cutâneas/patologia , Animais , Canais de Cálcio/genética , Canais de Cálcio/metabolismo , Proliferação de Células , Transformação Celular Neoplásica/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Perfilação da Expressão Gênica , Regulação Neoplásica da Expressão Gênica , Loci Gênicos , Discos Imaginais/metabolismo , Camundongos , Camundongos Knockout , Papiloma/genética , Fenótipo , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Homologia de Sequência do Ácido Nucleico , Pele/metabolismo , Pele/patologia , Neoplasias Cutâneas/genética , Asas de Animais/metabolismoRESUMO
During development and aging, animals suffer insults that modify the fitness of individual cells. In Drosophila, the elimination of viable but suboptimal cells is mediated by cell competition, ensuring that these cells do not accumulate during development. In addition, certain genes such as the Drosophila homolog of human c-myc (dmyc) are able to transform cells into supercompetitors, which eliminate neighboring wild-type cells by apoptosis and overproliferate, leaving total cell numbers unchanged. Here we have identified Drosophila Sparc as an early marker transcriptionally upregulated in loser cells that provides a transient protection by inhibiting Caspase activation in outcompeted cells. Overall, we describe the unexpected existence of a physiological mechanism that counteracts cell competition during development.
Assuntos
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/citologia , Drosophila melanogaster/metabolismo , Osteonectina/metabolismo , Transdução de Sinais , Animais , Apoptose , Biomarcadores/metabolismo , Linhagem Celular , Citoproteção , Proteínas de Drosophila/genética , Epistasia Genética , Osteonectina/genética , Regulação para Cima/genéticaRESUMO
Cell competition promotes the elimination of weaker cells from a growing population. Here we investigate how cells of Drosophila wing imaginal discs distinguish "winners" from "losers" during cell competition. Using genomic and functional assays, we have identified several factors implicated in the process, including Flower (Fwe), a cell membrane protein conserved in multicellular animals. Our results suggest that Fwe is a component of the cell competition response that is required and sufficient to label cells as "winners" or "losers." In Drosophila, the fwe locus produces three isoforms, fwe(ubi), fwe(Lose-A), and fwe(Lose-B). Basal levels of fwe(ubi) are constantly produced. During competition, the fwe(Lose) isoforms are upregulated in prospective loser cells. Cell-cell comparison of relative fwe(Lose) and fwe(ubi) levels ultimately determines which cell undergoes apoptosis. This "extracellular code" may constitute an ancient mechanism to terminate competitive conflicts among cells.
Assuntos
Apoptose/fisiologia , Canais de Cálcio/metabolismo , Diferenciação Celular/fisiologia , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/embriologia , Espaço Extracelular/metabolismo , Asas de Animais/embriologia , Animais , Canais de Cálcio/genética , Comunicação Celular/fisiologia , Membrana Celular/genética , Membrana Celular/metabolismo , Sobrevivência Celular/fisiologia , Proteínas de Drosophila/genética , Drosophila melanogaster/citologia , Espaço Extracelular/genética , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Organogênese/fisiologia , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Regulação para Cima/fisiologia , Asas de Animais/citologiaRESUMO
The proper development of tissues requires morphogen activity that dictates the appropriate growth and differentiation of each cell according to its position within a developing field. Elimination of underperforming cells that are less efficient in receiving/transducing the morphogenetic signal is thought to provide a general fail-safe mechanism to avoid developmental misspecification. In the developing Drosophila wing, the morphogen Dpp provides cells with growth and survival cues. Much of the regulation of transcriptional output by Dpp is mediated through repression of the transcriptional repressor Brinker (Brk), and thus through the activation of target genes. Mutant cells impaired for Dpp reception or transduction are lost from the wing epithelium. At the molecular level, reduced Dpp signaling results in Brk upregulation that triggers apoptosis through activation of the JNK pathway. Here we show that the transcriptional co-regulator dNAB is a Dpp target in the developing wing that interacts with Brk to eliminate cells with reduced Dpp signaling through the JNK pathway. We further show that both dNAB and Brk are required for cell elimination induced by differential dMyc expression, a process that depends on reduced Dpp transduction in outcompeted cells. We propose a novel mechanism whereby the morphogen Dpp regulates the responsiveness to its own survival signal by inversely controlling the expression of a repressor, Brk, and its co-repressor, dNAB.