RESUMO
Centriole biogenesis, as in most organelle assemblies, involves the sequential recruitment of sub-structural elements that will support its function. To uncover this process, we correlated the spatial location of 24 centriolar proteins with structural features using expansion microscopy. A time-series reconstruction of protein distributions throughout human procentriole assembly unveiled the molecular architecture of the centriole biogenesis steps. We found that the process initiates with the formation of a naked cartwheel devoid of microtubules. Next, the bloom phase progresses with microtubule blade assembly, concomitantly with radial separation and rapid cartwheel growth. In the subsequent elongation phase, the tubulin backbone grows linearly with the recruitment of the A-C linker, followed by proteins of the inner scaffold (IS). By following six structural modules, we modeled 4D assembly of the human centriole. Collectively, this work provides a framework to investigate the spatial and temporal assembly of large macromolecules.
Assuntos
Centríolos , Microtúbulos , Centríolos/metabolismo , Humanos , Microtúbulos/metabolismo , Tubulina (Proteína)/metabolismo , Proteínas de Ciclo Celular/metabolismoRESUMO
Metazoan genomes are copied bidirectionally from thousands of replication origins. Replication initiation entails the assembly and activation of two CMG helicases (Cdc45â Mcm2-7â GINS) at each origin. This requires several replication firing factors (including TopBP1, RecQL4, and DONSON) whose exact roles are still under debate. How two helicases are correctly assembled and activated at each origin is a long-standing question. By visualizing the recruitment of GINS, Cdc45, TopBP1, RecQL4, and DONSON in real time, we uncovered that replication initiation is surprisingly dynamic. First, TopBP1 transiently binds to the origin and dissociates before the start of DNA synthesis. Second, two Cdc45 are recruited together, even though Cdc45 alone cannot dimerize. Next, two copies of DONSON and two GINS simultaneously arrive at the origin, completing the assembly of two CMG helicases. Finally, RecQL4 is recruited to the CMGâ DONSONâ DONSONâ CMG complex and promotes DONSON dissociation and CMG activation via its ATPase activity.
Assuntos
Proteínas de Ciclo Celular , Replicação do DNA , Imagem Individual de Molécula , Humanos , Proteínas de Ciclo Celular/metabolismo , Origem de Replicação , Animais , DNA Helicases/metabolismo , RecQ Helicases/metabolismo , Proteínas de Ligação a DNA/metabolismoRESUMO
Ubiquitin-dependent unfolding of the CMG helicase by VCP/p97 is required to terminate DNA replication. Other replisome components are not processed in the same fashion, suggesting that additional mechanisms underlie replication protein turnover. Here, we identify replisome factor interactions with a protein complex composed of AAA+ ATPases SPATA5-SPATA5L1 together with heterodimeric partners C1orf109-CINP (55LCC). An integrative structural biology approach revealed a molecular architecture of SPATA5-SPATA5L1 N-terminal domains interacting with C1orf109-CINP to form a funnel-like structure above a cylindrically shaped ATPase motor. Deficiency in the 55LCC complex elicited ubiquitin-independent proteotoxicity, replication stress, and severe chromosome instability. 55LCC showed ATPase activity that was specifically enhanced by replication fork DNA and was coupled to cysteine protease-dependent cleavage of replisome substrates in response to replication fork damage. These findings define 55LCC-mediated proteostasis as critical for replication fork progression and genome stability and provide a rationale for pathogenic variants seen in associated human neurodevelopmental disorders.
Assuntos
Adenosina Trifosfatases , Replicação do DNA , Instabilidade Genômica , Proteostase , Humanos , Adenosina Trifosfatases/metabolismo , Proteína com Valosina/metabolismo , Proteína com Valosina/genética , Células HEK293 , Proteínas de Ciclo Celular/metabolismo , ATPases Associadas a Diversas Atividades Celulares/metabolismo , ATPases Associadas a Diversas Atividades Celulares/genéticaRESUMO
Centromeres are scaffolds for the assembly of kinetochores that ensure chromosome segregation during cell division. How vertebrate centromeres obtain a three-dimensional structure to accomplish their primary function is unclear. Using super-resolution imaging, capture-C, and polymer modeling, we show that vertebrate centromeres are partitioned by condensins into two subdomains during mitosis. The bipartite structure is found in human, mouse, and chicken cells and is therefore a fundamental feature of vertebrate centromeres. Super-resolution imaging and electron tomography reveal that bipartite centromeres assemble bipartite kinetochores, with each subdomain binding a distinct microtubule bundle. Cohesin links the centromere subdomains, limiting their separation in response to spindle forces and avoiding merotelic kinetochore-spindle attachments. Lagging chromosomes during cancer cell divisions frequently have merotelic attachments in which the centromere subdomains are separated and bioriented. Our work reveals a fundamental aspect of vertebrate centromere biology with implications for understanding the mechanisms that guarantee faithful chromosome segregation.
Assuntos
Centrômero , Coesinas , Cinetocoros , Mitose , Animais , Humanos , Camundongos , Proteínas de Ciclo Celular/metabolismo , Centrômero/metabolismo , Galinhas , Proteínas Cromossômicas não Histona/metabolismo , Proteínas Cromossômicas não Histona/química , Segregação de Cromossomos , Cinetocoros/metabolismo , Microtúbulos/metabolismo , Fuso Acromático/metabolismoRESUMO
In eukaryotes, the Suv39 family of proteins tri-methylate lysine 9 of histone H3 (H3K9me) to form constitutive heterochromatin. However, how Suv39 proteins are nucleated at heterochromatin is not fully described. In the fission yeast, current models posit that Argonaute1-associated small RNAs (sRNAs) nucleate the sole H3K9 methyltransferase, Clr4/SUV39H, to centromeres. Here, we show that in the absence of all sRNAs and H3K9me, the Mtl1 and Red1 core (MTREC)/PAXT complex nucleates Clr4/SUV39H at a heterochromatic long noncoding RNA (lncRNA) at which the two H3K9 deacetylases, Sir2 and Clr3, also accumulate by distinct mechanisms. Iterative cycles of H3K9 deacetylation and methylation spread Clr4/SUV39H from the nucleation center in an sRNA-independent manner, generating a basal H3K9me state. This is acted upon by the RNAi machinery to augment and amplify the Clr4/H3K9me signal at centromeres to establish heterochromatin. Overall, our data reveal that lncRNAs and RNA quality control factors can nucleate heterochromatin and function as epigenetic silencers in eukaryotes.
Assuntos
Proteínas de Ciclo Celular , Heterocromatina , Histona-Lisina N-Metiltransferase , Histonas , Proteínas de Schizosaccharomyces pombe , Schizosaccharomyces , Proteínas de Ciclo Celular/metabolismo , Centrômero/metabolismo , Heterocromatina/metabolismo , Histona-Lisina N-Metiltransferase/metabolismo , Histonas/metabolismo , Metilação , Metiltransferases/metabolismo , RNA Longo não Codificante/metabolismo , RNA Longo não Codificante/genética , Schizosaccharomyces/metabolismo , Schizosaccharomyces/genética , Proteínas de Schizosaccharomyces pombe/metabolismo , RNA Fúngico/genética , RNA Interferente Pequeno/genéticaRESUMO
SMC (structural maintenance of chromosomes) protein complexes are an evolutionarily conserved family of motor proteins that hold sister chromatids together and fold genomes throughout the cell cycle by DNA loop extrusion. These complexes play a key role in a variety of functions in the packaging and regulation of chromosomes, and they have been intensely studied in recent years. Despite their importance, the detailed molecular mechanism for DNA loop extrusion by SMC complexes remains unresolved. Here, we describe the roles of SMCs in chromosome biology and particularly review in vitro single-molecule studies that have recently advanced our understanding of SMC proteins. We describe the mechanistic biophysical aspects of loop extrusion that govern genome organization and its consequences.
Assuntos
Proteínas Cromossômicas não Histona , Complexos Multiproteicos , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/metabolismo , Complexos Multiproteicos/química , Cromossomos/genética , Cromossomos/metabolismo , DNA/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismoRESUMO
In eukaryotes, DNA replication initiation requires assembly and activation of the minichromosome maintenance (MCM) 2-7 double hexamer (DH) to melt origin DNA strands. However, the mechanism for this initial melting is unknown. Here, we report a 2.59-Å cryo-electron microscopy structure of the human MCM-DH (hMCM-DH), also known as the pre-replication complex. In this structure, the hMCM-DH with a constricted central channel untwists and stretches the DNA strands such that almost a half turn of the bound duplex DNA is distorted with 1 base pair completely separated, generating an initial open structure (IOS) at the hexamer junction. Disturbing the IOS inhibits DH formation and replication initiation. Mapping of hMCM-DH footprints indicates that IOSs are distributed across the genome in large clusters aligning well with initiation zones designed for stochastic origin firing. This work unravels an intrinsic mechanism that couples DH formation with initial DNA melting to license replication initiation in human cells.
Assuntos
Replicação do DNA , Humanos , Proteínas de Ciclo Celular/metabolismo , Microscopia Crioeletrônica , Proteínas de Ligação a DNA/metabolismo , Proteínas de Manutenção de Minicromossomo/metabolismo , Origem de ReplicaçãoRESUMO
CDK2 is a core cell-cycle kinase that phosphorylates many substrates to drive progression through the cell cycle. CDK2 is hyperactivated in multiple cancers and is therefore an attractive therapeutic target. Here, we use several CDK2 inhibitors in clinical development to interrogate CDK2 substrate phosphorylation, cell-cycle progression, and drug adaptation in preclinical models. Whereas CDK1 is known to compensate for loss of CDK2 in Cdk2-/- mice, this is not true of acute inhibition of CDK2. Upon CDK2 inhibition, cells exhibit a rapid loss of substrate phosphorylation that rebounds within several hours. CDK4/6 activity backstops inhibition of CDK2 and sustains the proliferative program by maintaining Rb1 hyperphosphorylation, active E2F transcription, and cyclin A2 expression, enabling re-activation of CDK2 in the presence of drug. Our results augment our understanding of CDK plasticity and indicate that co-inhibition of CDK2 and CDK4/6 may be required to suppress adaptation to CDK2 inhibitors currently under clinical assessment.
Assuntos
Proteínas de Ciclo Celular , Quinases Ciclina-Dependentes , Animais , Camundongos , Quinases Ciclina-Dependentes/metabolismo , Ciclo Celular/fisiologia , Quinase 2 Dependente de Ciclina/genética , Quinase 2 Dependente de Ciclina/metabolismo , Proteínas de Ciclo Celular/metabolismo , Fosforilação , Divisão CelularRESUMO
Human inherited disorders of interferon-gamma (IFN-γ) immunity underlie severe mycobacterial diseases. We report X-linked recessive MCTS1 deficiency in men with mycobacterial disease from kindreds of different ancestries (from China, Finland, Iran, and Saudi Arabia). Complete deficiency of this translation re-initiation factor impairs the translation of a subset of proteins, including the kinase JAK2 in all cell types tested, including T lymphocytes and phagocytes. JAK2 expression is sufficiently low to impair cellular responses to interleukin-23 (IL-23) and partially IL-12, but not other JAK2-dependent cytokines. Defective responses to IL-23 preferentially impair the production of IFN-γ by innate-like adaptive mucosal-associated invariant T cells (MAIT) and γδ T lymphocytes upon mycobacterial challenge. Surprisingly, the lack of MCTS1-dependent translation re-initiation and ribosome recycling seems to be otherwise physiologically redundant in these patients. These findings suggest that X-linked recessive human MCTS1 deficiency underlies isolated mycobacterial disease by impairing JAK2 translation in innate-like adaptive T lymphocytes, thereby impairing the IL-23-dependent induction of IFN-γ.
Assuntos
Interferon gama , Janus Quinase 2 , Infecções por Mycobacterium , Humanos , Masculino , Proteínas de Ciclo Celular/metabolismo , Interferon gama/imunologia , Interleucina-12 , Interleucina-23 , Janus Quinase 2/metabolismo , Mycobacterium/fisiologia , Infecções por Mycobacterium/imunologia , Infecções por Mycobacterium/metabolismo , Proteínas Oncogênicas/metabolismoRESUMO
Concomitant with DNA replication, the chromosomal cohesin complex establishes cohesion between newly replicated sister chromatids. Cohesion establishment requires acetylation of conserved cohesin lysine residues by Eco1 acetyltransferase. Here, we explore how cohesin acetylation is linked to DNA replication. Biochemical reconstitution of replication-coupled cohesin acetylation reveals that transient DNA structures, which form during DNA replication, control the acetylation reaction. As polymerases complete lagging strand replication, strand displacement synthesis produces DNA flaps that are trimmed to result in nicked double-stranded DNA. Both flaps and nicks stimulate cohesin acetylation, while subsequent nick ligation to complete Okazaki fragment maturation terminates the acetylation reaction. A flapped or nicked DNA substrate constitutes a transient molecular clue that directs cohesin acetylation to a window behind the replication fork, next to where cohesin likely entraps both sister chromatids. Our results provide an explanation for how DNA replication is linked to sister chromatid cohesion establishment.
Assuntos
Cromátides , Proteínas de Saccharomyces cerevisiae , Cromátides/metabolismo , Proteínas Nucleares/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Replicação do DNA , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , DNA , Acetiltransferases/genética , Acetiltransferases/metabolismoRESUMO
The mechanism that initiates autophagosome formation on the ER in multicellular organisms is elusive. Here, we showed that autophagy stimuli trigger Ca2+ transients on the outer surface of the ER membrane, whose amplitude, frequency, and duration are controlled by the metazoan-specific ER transmembrane autophagy protein EPG-4/EI24. Persistent Ca2+ transients/oscillations on the cytosolic ER surface in EI24-depleted cells cause accumulation of FIP200 autophagosome initiation complexes on the ER. This defect is suppressed by attenuating ER Ca2+ transients. Multi-modal SIM analysis revealed that Ca2+ transients on the ER trigger the formation of dynamic and fusion-prone liquid-like FIP200 puncta. Starvation-induced Ca2+ transients on lysosomes also induce FIP200 puncta that further move to the ER. Multiple FIP200 puncta on the ER, whose association depends on the ER proteins VAPA/B and ATL2/3, assemble into autophagosome formation sites. Thus, Ca2+ transients are crucial for triggering phase separation of FIP200 to specify autophagosome initiation sites in metazoans.
Assuntos
Autofagossomos , Cálcio , Animais , Autofagossomos/metabolismo , Cálcio/metabolismo , Retículo Endoplasmático/metabolismo , Proteínas Relacionadas à Autofagia/metabolismo , Autofagia , Proteínas de Ciclo Celular/metabolismoRESUMO
Treatment of severe COVID-19 is currently limited by clinical heterogeneity and incomplete description of specific immune biomarkers. We present here a comprehensive multi-omic blood atlas for patients with varying COVID-19 severity in an integrated comparison with influenza and sepsis patients versus healthy volunteers. We identify immune signatures and correlates of host response. Hallmarks of disease severity involved cells, their inflammatory mediators and networks, including progenitor cells and specific myeloid and lymphocyte subsets, features of the immune repertoire, acute phase response, metabolism, and coagulation. Persisting immune activation involving AP-1/p38MAPK was a specific feature of COVID-19. The plasma proteome enabled sub-phenotyping into patient clusters, predictive of severity and outcome. Systems-based integrative analyses including tensor and matrix decomposition of all modalities revealed feature groupings linked with severity and specificity compared to influenza and sepsis. Our approach and blood atlas will support future drug development, clinical trial design, and personalized medicine approaches for COVID-19.
Assuntos
Biomarcadores/sangue , COVID-19/patologia , Proteoma/análise , Adulto , Proteínas Sanguíneas/metabolismo , COVID-19/sangue , COVID-19/virologia , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Feminino , Humanos , Influenza Humana/sangue , Influenza Humana/patologia , Linfócitos/imunologia , Linfócitos/metabolismo , Aprendizado de Máquina , Masculino , Pessoa de Meia-Idade , Proteína Quinase 14 Ativada por Mitógeno/genética , Proteína Quinase 14 Ativada por Mitógeno/metabolismo , Monócitos/imunologia , Monócitos/metabolismo , Análise de Componente Principal , SARS-CoV-2/isolamento & purificação , Sepse/sangue , Sepse/patologia , Índice de Gravidade de Doença , Fator de Transcrição AP-1/genética , Fator de Transcrição AP-1/metabolismoRESUMO
Lymphocyte development consists of sequential and mutually exclusive cell states of proliferative selection and antigen receptor gene recombination. Transitions between each state require large, coordinated changes in epigenetic landscapes and transcriptional programs. How this occurs remains unclear. Here we demonstrate that in small pre-B cells, the lineage and stage-specific epigenetic reader bromodomain and WD repeat-containing protein 1 (BRWD1) reorders three-dimensional chromatin topology to affect the transition between proliferative and gene recombination molecular programs. BRWD1 regulated the switch between poised and active enhancers interacting with promoters, and coordinated this switch with Igk locus contraction. BRWD1 did so by converting chromatin-bound static to dynamic cohesin competent to mediate long-range looping. ATP-depletion revealed cohesin conversion to be the main energetic mechanism dictating dynamic chromatin looping. Our findings provide a new mechanism of cohesin regulation and reveal how cohesin function can be dictated by lineage contextual mechanisms to facilitate specific cell fate transitions.
Assuntos
Cromatina , Coesinas , Cromatina/genética , Células Precursoras de Linfócitos B , Regulação da Expressão Gênica , Diferenciação Celular , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismoRESUMO
Structural maintenance of chromosomes (SMC) complexes organize genome topology in all kingdoms of life and have been proposed to perform this function by DNA loop extrusion. How this process works is unknown. Here, we have analyzed how loop extrusion is mediated by human cohesin-NIPBL complexes, which enable chromatin folding in interphase cells. We have identified DNA binding sites and large-scale conformational changes that are required for loop extrusion and have determined how these are coordinated. Our results suggest that DNA is translocated by a spontaneous 50 nm-swing of cohesin's hinge, which hands DNA over to the ATPase head of SMC3, where upon binding of ATP, DNA is clamped by NIPBL. During this process, NIPBL "jumps ship" from the hinge toward the SMC3 head and might thereby couple the spontaneous hinge swing to ATP-dependent DNA clamping. These results reveal mechanistic principles of how cohesin-NIPBL and possibly other SMC complexes mediate loop extrusion.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , DNA/química , Conformação de Ácido Nucleico , Adenosina Trifosfatases/metabolismo , Trifosfato de Adenosina/metabolismo , Sítios de Ligação , Proteínas de Ciclo Celular/química , DNA/metabolismo , Transferência Ressonante de Energia de Fluorescência , Células HeLa , Humanos , Hidrólise , Cinética , Microscopia de Força Atômica , Modelos Moleculares , Proteínas Nucleares/metabolismo , Conformação Proteica , CoesinasRESUMO
Searching for factors to improve knockin efficiency for therapeutic applications, biotechnology, and generation of non-human primate models of disease, we found that the strand exchange protein RAD51 can significantly increase Cas9-mediated homozygous knockin in mouse embryos through an interhomolog repair (IHR) mechanism. IHR is a hallmark of meiosis but only occurs at low frequencies in somatic cells, and its occurrence in zygotes is controversial. Using multiple approaches, we provide evidence for an endogenous IHR mechanism in the early embryo that can be enhanced by RAD51. This process can be harnessed to generate homozygotes from wild-type zygotes using exogenous donors and to convert heterozygous alleles into homozygous alleles without exogenous templates. Furthermore, we identify additional IHR-promoting factors and describe features of IHR events. Together, our findings show conclusive evidence for IHR in mouse embryos and describe an efficient method for enhanced gene conversion.
Assuntos
Reparo do DNA/genética , Conversão Gênica , Rad51 Recombinase/metabolismo , Alelos , Animais , Sequência de Bases , Proteína 9 Associada à CRISPR/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Proteínas de Ciclo Celular/metabolismo , Cromossomos de Mamíferos/genética , Quebras de DNA de Cadeia Dupla , Embrião de Mamíferos , Feminino , Loci Gênicos , Recombinação Homóloga/genética , Homozigoto , Humanos , Mutação INDEL/genética , Camundongos Endogâmicos C57BL , Mosaicismo , Proteínas Nucleares/metabolismo , Polimorfismo de Nucleotídeo Único/genética , Ribonucleoproteínas/metabolismo , Zigoto/metabolismoRESUMO
Cardiac injury and dysfunction occur in COVID-19 patients and increase the risk of mortality. Causes are ill defined but could be through direct cardiac infection and/or inflammation-induced dysfunction. To identify mechanisms and cardio-protective drugs, we use a state-of-the-art pipeline combining human cardiac organoids with phosphoproteomics and single nuclei RNA sequencing. We identify an inflammatory "cytokine-storm", a cocktail of interferon gamma, interleukin 1ß, and poly(I:C), induced diastolic dysfunction. Bromodomain-containing protein 4 is activated along with a viral response that is consistent in both human cardiac organoids (hCOs) and hearts of SARS-CoV-2-infected K18-hACE2 mice. Bromodomain and extraterminal family inhibitors (BETi) recover dysfunction in hCOs and completely prevent cardiac dysfunction and death in a mouse cytokine-storm model. Additionally, BETi decreases transcription of genes in the viral response, decreases ACE2 expression, and reduces SARS-CoV-2 infection of cardiomyocytes. Together, BETi, including the Food and Drug Administration (FDA) breakthrough designated drug, apabetalone, are promising candidates to prevent COVID-19 mediated cardiac damage.
Assuntos
COVID-19/complicações , Cardiotônicos/uso terapêutico , Proteínas de Ciclo Celular/antagonistas & inibidores , Cardiopatias/tratamento farmacológico , Quinazolinonas/uso terapêutico , Fatores de Transcrição/antagonistas & inibidores , Enzima de Conversão de Angiotensina 2/metabolismo , Animais , Proteínas de Ciclo Celular/metabolismo , Linhagem Celular , Citocinas/metabolismo , Feminino , Cardiopatias/etiologia , Células-Tronco Embrionárias Humanas , Humanos , Inflamação/complicações , Inflamação/tratamento farmacológico , Camundongos , Camundongos Endogâmicos C57BL , Fatores de Transcrição/metabolismo , Tratamento Farmacológico da COVID-19RESUMO
Although oxidative phosphorylation is best known for producing ATP, it also yields reactive oxygen species (ROS) as invariant byproducts. Depletion of ROS below their physiological levels, a phenomenon known as reductive stress, impedes cellular signaling and has been linked to cancer, diabetes, and cardiomyopathy. Cells alleviate reductive stress by ubiquitylating and degrading the mitochondrial gatekeeper FNIP1, yet it is unknown how the responsible E3 ligase CUL2FEM1B can bind its target based on redox state and how this is adjusted to changing cellular environments. Here, we show that CUL2FEM1B relies on zinc as a molecular glue to selectively recruit reduced FNIP1 during reductive stress. FNIP1 ubiquitylation is gated by pseudosubstrate inhibitors of the BEX family, which prevent premature FNIP1 degradation to protect cells from unwarranted ROS accumulation. FEM1B gain-of-function mutation and BEX deletion elicit similar developmental syndromes, showing that the zinc-dependent reductive stress response must be tightly regulated to maintain cellular and organismal homeostasis.
Assuntos
Estresse Fisiológico , Aminoácidos/química , Animais , Proteínas de Transporte/química , Proteínas de Transporte/metabolismo , Proteínas de Ciclo Celular/química , Proteínas de Ciclo Celular/metabolismo , Linhagem Celular , Feminino , Humanos , Íons , Camundongos , Proteínas Mutantes/metabolismo , Mutação/genética , Ligação Proteica/efeitos dos fármacos , Estabilidade Proteica/efeitos dos fármacos , Espécies Reativas de Oxigênio/metabolismo , Estresse Fisiológico/efeitos dos fármacos , Relação Estrutura-Atividade , Especificidade por Substrato/efeitos dos fármacos , Complexos Ubiquitina-Proteína Ligase/química , Complexos Ubiquitina-Proteína Ligase/metabolismo , Ubiquitinação/efeitos dos fármacos , Zinco/farmacologiaRESUMO
The anaphase-promoting complex/cyclosome (APC/C) represents a large multisubunit E3-ubiquitin ligase complex that controls the unidirectional progression through the cell cycle by the ubiquitination of specific target proteins, marking them for proteasomal destruction. Although the APC/C's role is largely conserved among eukaryotes, its subunit composition and target spectrum appear to be species specific. In this review, we focus on the plant APC/C complex, whose activity correlates with different developmental processes, including polyploidization and gametogenesis. After an introduction into proteolytic control by ubiquitination, we discuss the composition of the plant APC/C and the essential nature of its core subunits for plant development. Subsequently, we describe the APC/C activator subunits and interactors, most being plant specific. Finally, we provide a comprehensive list of confirmed and suspected plant APC/C target proteins. Identification of growth-related targets might offer opportunities to increase crop yield and resilience of plants to climate change by manipulating APC/C activity.
Assuntos
Anáfase , Plantas , Ciclossomo-Complexo Promotor de Anáfase/genética , Ciclossomo-Complexo Promotor de Anáfase/metabolismo , Ciclo Celular , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Plantas/genética , Plantas/metabolismo , Ubiquitinação , Ubiquitinas/metabolismoRESUMO
In eukaryotes, heterochromatin is generally located at the nuclear periphery. This study investigates the biological significance of perinuclear positioning for heterochromatin maintenance and gene silencing. We identify the nuclear rim protein Amo1NUPL2 as a factor required for the propagation of heterochromatin at endogenous and ectopic sites in the fission yeast genome. Amo1 associates with the Rix1PELP1-containing RNA processing complex RIXC and with the histone chaperone complex FACT. RIXC, which binds to heterochromatin protein Swi6HP1 across silenced chromosomal domains and to surrounding boundary elements, connects heterochromatin with Amo1 at the nuclear periphery. In turn, the Amo1-enriched subdomain is critical for Swi6 association with FACT that precludes histone turnover to promote gene silencing and preserve epigenetic stability of heterochromatin. In addition to uncovering conserved factors required for perinuclear positioning of heterochromatin, these analyses elucidate a mechanism by which a peripheral subdomain enforces stable gene repression and maintains heterochromatin in a heritable manner.
Assuntos
Epigênese Genética/genética , Heterocromatina/genética , Heterocromatina/metabolismo , Proteínas de Ciclo Celular/metabolismo , Núcleo Celular/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Repressão Epigenética/genética , Inativação Gênica , Hereditariedade , Histonas/genética , Histonas/metabolismo , Metilação , Proteínas Nucleares/metabolismo , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismo , Proteínas de Schizosaccharomyces pombe/genética , Proteínas de Schizosaccharomyces pombe/metabolismoRESUMO
The accurate timing and execution of organelle biogenesis is crucial for cell physiology. Centriole biogenesis is regulated by Polo-like kinase 4 (Plk4) and initiates in S-phase when a daughter centriole grows from the side of a pre-existing mother. Here, we show that a Plk4 oscillation at the base of the growing centriole initiates and times centriole biogenesis to ensure that centrioles grow at the right time and to the right size. The Plk4 oscillation is normally entrained to the cell-cycle oscillator but can run autonomously of it-potentially explaining why centrioles can duplicate independently of cell-cycle progression. Mathematical modeling indicates that the Plk4 oscillation can be generated by a time-delayed negative feedback loop in which Plk4 inactivates the interaction with its centriolar receptor through multiple rounds of phosphorylation. We hypothesize that similar organelle-specific oscillations could regulate the timing and execution of organelle biogenesis more generally.