Pub Date : 2024-08-05Epub Date: 2024-06-12DOI: 10.1083/jcb.202311073
Ivan R Nabi, Ben Cardoen, Ismail M Khater, Guang Gao, Timothy H Wong, Ghassan Hamarneh
Super-resolution microscopy, or nanoscopy, enables the use of fluorescent-based molecular localization tools to study molecular structure at the nanoscale level in the intact cell, bridging the mesoscale gap to classical structural biology methodologies. Analysis of super-resolution data by artificial intelligence (AI), such as machine learning, offers tremendous potential for the discovery of new biology, that, by definition, is not known and lacks ground truth. Herein, we describe the application of weakly supervised paradigms to super-resolution microscopy and its potential to enable the accelerated exploration of the nanoscale architecture of subcellular macromolecules and organelles.
{"title":"AI analysis of super-resolution microscopy: Biological discovery in the absence of ground truth.","authors":"Ivan R Nabi, Ben Cardoen, Ismail M Khater, Guang Gao, Timothy H Wong, Ghassan Hamarneh","doi":"10.1083/jcb.202311073","DOIUrl":"10.1083/jcb.202311073","url":null,"abstract":"<p><p>Super-resolution microscopy, or nanoscopy, enables the use of fluorescent-based molecular localization tools to study molecular structure at the nanoscale level in the intact cell, bridging the mesoscale gap to classical structural biology methodologies. Analysis of super-resolution data by artificial intelligence (AI), such as machine learning, offers tremendous potential for the discovery of new biology, that, by definition, is not known and lacks ground truth. Herein, we describe the application of weakly supervised paradigms to super-resolution microscopy and its potential to enable the accelerated exploration of the nanoscale architecture of subcellular macromolecules and organelles.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.8,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11169916/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141305976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-05Epub Date: 2024-07-16DOI: 10.1083/jcb.202311153
Alexandre Thomas, Patrick Meraldi
Centrosomes are the main microtubule-organizing centers in animal cells. Due to the semiconservative nature of centrosome duplication, the two centrosomes differ in age. In asymmetric stem cell divisions, centrosome age can induce an asymmetry in half-spindle lengths. However, whether centrosome age affects the symmetry of the two half-spindles in tissue culture cells thought to divide symmetrically is unknown. Here, we show that in human epithelial and fibroblastic cell lines centrosome age imposes a mild spindle asymmetry that leads to asymmetric cell daughter sizes. At the mechanistic level, we show that this asymmetry depends on a cenexin-bound pool of the mitotic kinase Plk1, which favors the preferential accumulation on old centrosomes of the microtubule nucleation-organizing proteins pericentrin, γ-tubulin, and Cdk5Rap2, and microtubule regulators TPX2 and ch-TOG. Consistently, we find that old centrosomes have a higher microtubule nucleation capacity. We postulate that centrosome age breaks spindle size symmetry via microtubule nucleation even in cells thought to divide symmetrically.
{"title":"Centrosome age breaks spindle size symmetry even in cells thought to divide symmetrically.","authors":"Alexandre Thomas, Patrick Meraldi","doi":"10.1083/jcb.202311153","DOIUrl":"10.1083/jcb.202311153","url":null,"abstract":"<p><p>Centrosomes are the main microtubule-organizing centers in animal cells. Due to the semiconservative nature of centrosome duplication, the two centrosomes differ in age. In asymmetric stem cell divisions, centrosome age can induce an asymmetry in half-spindle lengths. However, whether centrosome age affects the symmetry of the two half-spindles in tissue culture cells thought to divide symmetrically is unknown. Here, we show that in human epithelial and fibroblastic cell lines centrosome age imposes a mild spindle asymmetry that leads to asymmetric cell daughter sizes. At the mechanistic level, we show that this asymmetry depends on a cenexin-bound pool of the mitotic kinase Plk1, which favors the preferential accumulation on old centrosomes of the microtubule nucleation-organizing proteins pericentrin, γ-tubulin, and Cdk5Rap2, and microtubule regulators TPX2 and ch-TOG. Consistently, we find that old centrosomes have a higher microtubule nucleation capacity. We postulate that centrosome age breaks spindle size symmetry via microtubule nucleation even in cells thought to divide symmetrically.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.4,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11252449/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141620073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-05Epub Date: 2024-05-10DOI: 10.1083/jcb.202403020
Gabriella S Darmasaputra, Cindy C Geerlings, Susana M Chuva de Sousa Lopes, Hans Clevers, Matilde Galli
Binucleated polyploid cells are common in many animal tissues, where they arise by endomitosis, a non-canonical cell cycle in which cells enter M phase but do not undergo cytokinesis. Different steps of cytokinesis have been shown to be inhibited during endomitosis M phase in rodents, but it is currently unknown how human cells undergo endomitosis. In this study, we use fetal-derived human hepatocyte organoids (Hep-Orgs) to investigate how human hepatocytes initiate and execute endomitosis. We find that cells in endomitosis M phase have normal mitotic timings, but lose membrane anchorage to the midbody during cytokinesis, which is associated with the loss of four cortical anchoring proteins, RacGAP1, Anillin, SEPT9, and citron kinase (CIT-K). Moreover, reduction of WNT activity increases the percentage of binucleated cells in Hep-Orgs, an effect that is dependent on the atypical E2F proteins, E2F7 and E2F8. Together, we have elucidated how hepatocytes undergo endomitosis in human Hep-Orgs, providing new insights into the mechanisms of endomitosis in mammals.
双核多倍体细胞在许多动物组织中都很常见,它们是通过内异生产生的,内异生是一种非规范细胞周期,细胞进入 M 期但不进行细胞分裂。在啮齿类动物中,细胞分裂的不同步骤已被证明在内生 M 期受到抑制,但目前还不清楚人类细胞是如何进行内生的。在本研究中,我们利用胎儿衍生的人类肝细胞器官组织(Hep-Orgs)来研究人类肝细胞如何启动和执行内膜形成。我们发现,处于内膜有丝分裂 M 期的细胞具有正常的有丝分裂时间,但在细胞分裂过程中会失去与中体的膜锚定,这与四种皮质锚定蛋白 RacGAP1、Anillin、SEPT9 和柠檬激酶(CIT-K)的缺失有关。此外,减少 WNT 活性会增加 Hep-Orgs 中双核细胞的比例,这种效应依赖于非典型 E2F 蛋白 E2F7 和 E2F8。综上所述,我们阐明了人类 Hep-Orgs 中的肝细胞是如何发生内异症的,从而为哺乳动物的内异症机制提供了新的见解。
{"title":"Binucleated human hepatocytes arise through late cytokinetic regression during endomitosis M phase.","authors":"Gabriella S Darmasaputra, Cindy C Geerlings, Susana M Chuva de Sousa Lopes, Hans Clevers, Matilde Galli","doi":"10.1083/jcb.202403020","DOIUrl":"10.1083/jcb.202403020","url":null,"abstract":"<p><p>Binucleated polyploid cells are common in many animal tissues, where they arise by endomitosis, a non-canonical cell cycle in which cells enter M phase but do not undergo cytokinesis. Different steps of cytokinesis have been shown to be inhibited during endomitosis M phase in rodents, but it is currently unknown how human cells undergo endomitosis. In this study, we use fetal-derived human hepatocyte organoids (Hep-Orgs) to investigate how human hepatocytes initiate and execute endomitosis. We find that cells in endomitosis M phase have normal mitotic timings, but lose membrane anchorage to the midbody during cytokinesis, which is associated with the loss of four cortical anchoring proteins, RacGAP1, Anillin, SEPT9, and citron kinase (CIT-K). Moreover, reduction of WNT activity increases the percentage of binucleated cells in Hep-Orgs, an effect that is dependent on the atypical E2F proteins, E2F7 and E2F8. Together, we have elucidated how hepatocytes undergo endomitosis in human Hep-Orgs, providing new insights into the mechanisms of endomitosis in mammals.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.8,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11090133/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140898469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The double-stranded RNA-binding protein Staufen1 (STAU1) regulates a variety of physiological and pathological events via mediating RNA metabolism. STAU1 overabundance was observed in tissues from mouse models and fibroblasts from patients with neurodegenerative diseases, accompanied by enhanced mTOR signaling and impaired autophagic flux, while the underlying mechanism remains elusive. Here, we find that endogenous STAU1 forms dynamic cytoplasmic condensate in normal and tumor cell lines, as well as in mouse Huntington's disease knockin striatal cells. STAU1 condensate recruits target mRNA MTOR at its 5'UTR and promotes its translation both in vitro and in vivo, and thus enhanced formation of STAU1 condensate leads to mTOR hyperactivation and autophagy-lysosome dysfunction. Interference of STAU1 condensate normalizes mTOR levels, ameliorates autophagy-lysosome function, and reduces aggregation of pathological proteins in cellular models of neurodegenerative diseases. These findings highlight the importance of balanced phase separation in physiological processes, suggesting that modulating STAU1 condensate may be a strategy to mitigate the progression of neurodegenerative diseases with STAU1 overabundance.
{"title":"Excessive STAU1 condensate drives mTOR translation and autophagy dysfunction in neurodegeneration.","authors":"Ruiqian Zhao, Shijing Huang, Jingyu Li, Aihong Gu, Minjie Fu, Wei Hua, Ying Mao, Qun-Ying Lei, Boxun Lu, Wenyu Wen","doi":"10.1083/jcb.202311127","DOIUrl":"10.1083/jcb.202311127","url":null,"abstract":"<p><p>The double-stranded RNA-binding protein Staufen1 (STAU1) regulates a variety of physiological and pathological events via mediating RNA metabolism. STAU1 overabundance was observed in tissues from mouse models and fibroblasts from patients with neurodegenerative diseases, accompanied by enhanced mTOR signaling and impaired autophagic flux, while the underlying mechanism remains elusive. Here, we find that endogenous STAU1 forms dynamic cytoplasmic condensate in normal and tumor cell lines, as well as in mouse Huntington's disease knockin striatal cells. STAU1 condensate recruits target mRNA MTOR at its 5'UTR and promotes its translation both in vitro and in vivo, and thus enhanced formation of STAU1 condensate leads to mTOR hyperactivation and autophagy-lysosome dysfunction. Interference of STAU1 condensate normalizes mTOR levels, ameliorates autophagy-lysosome function, and reduces aggregation of pathological proteins in cellular models of neurodegenerative diseases. These findings highlight the importance of balanced phase separation in physiological processes, suggesting that modulating STAU1 condensate may be a strategy to mitigate the progression of neurodegenerative diseases with STAU1 overabundance.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.4,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11194678/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141442741","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-05Epub Date: 2024-05-20DOI: 10.1083/jcb.202402046
Jennifer E Gilda, Asrafun Nahar, Dharanibalan Kasiviswanathan, Nadav Tropp, Tamar Gilinski, Tamar Lahav, Dina Alexandrovich, Yael Mandel-Gutfreund, Soyeon Park, Shenhav Shemer
Proteasome activity is crucial for cellular integrity, but how tissues adjust proteasome content in response to catabolic stimuli is uncertain. Here, we demonstrate that transcriptional coordination by multiple transcription factors is required to increase proteasome content and activate proteolysis in catabolic states. Using denervated mouse muscle as a model system for accelerated proteolysis in vivo, we reveal that a two-phase transcriptional program activates genes encoding proteasome subunits and assembly chaperones to boost an increase in proteasome content. Initially, gene induction is necessary to maintain basal proteasome levels, and in a more delayed phase (7-10 days after denervation), it stimulates proteasome assembly to meet cellular demand for excessive proteolysis. Intriguingly, the transcription factors PAX4 and α-PALNRF-1 control the expression of proteasome among other genes in a combinatorial manner, driving cellular adaptation to muscle denervation. Consequently, PAX4 and α-PALNRF-1 represent new therapeutic targets to inhibit proteolysis in catabolic diseases (e.g., type-2 diabetes, cancer).
{"title":"Proteasome gene expression is controlled by coordinated functions of multiple transcription factors.","authors":"Jennifer E Gilda, Asrafun Nahar, Dharanibalan Kasiviswanathan, Nadav Tropp, Tamar Gilinski, Tamar Lahav, Dina Alexandrovich, Yael Mandel-Gutfreund, Soyeon Park, Shenhav Shemer","doi":"10.1083/jcb.202402046","DOIUrl":"10.1083/jcb.202402046","url":null,"abstract":"<p><p>Proteasome activity is crucial for cellular integrity, but how tissues adjust proteasome content in response to catabolic stimuli is uncertain. Here, we demonstrate that transcriptional coordination by multiple transcription factors is required to increase proteasome content and activate proteolysis in catabolic states. Using denervated mouse muscle as a model system for accelerated proteolysis in vivo, we reveal that a two-phase transcriptional program activates genes encoding proteasome subunits and assembly chaperones to boost an increase in proteasome content. Initially, gene induction is necessary to maintain basal proteasome levels, and in a more delayed phase (7-10 days after denervation), it stimulates proteasome assembly to meet cellular demand for excessive proteolysis. Intriguingly, the transcription factors PAX4 and α-PALNRF-1 control the expression of proteasome among other genes in a combinatorial manner, driving cellular adaptation to muscle denervation. Consequently, PAX4 and α-PALNRF-1 represent new therapeutic targets to inhibit proteolysis in catabolic diseases (e.g., type-2 diabetes, cancer).</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.8,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11104393/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141065337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-05Epub Date: 2024-06-12DOI: 10.1083/jcb.202401112
Anda Huna, Amélie Massemin, Gabriela Makulyte, Jean-Michel Flaman, Nadine Martin, David Bernard
During aging and in some contexts, like embryonic development, wound healing, and diseases such as cancer, senescent cells accumulate and play a key role in different pathophysiological functions. A long-held belief was that cellular senescence decreased normal cell functions, given the loss of proliferation of senescent cells. This view radically changed following the discovery of the senescence-associated secretory phenotype (SASP), factors released by senescent cells into their microenvironment. There is now accumulating evidence that cellular senescence also promotes gain-of-function effects by establishing, reinforcing, or changing cell identity, which can have a beneficial or deleterious impact on pathophysiology. These effects may involve both proliferation arrest and autocrine SASP production, although they largely remain to be defined. Here, we provide a historical overview of the first studies on senescence and an insight into emerging trends regarding the effects of senescence on cell identity.
{"title":"Regulation of cell function and identity by cellular senescence.","authors":"Anda Huna, Amélie Massemin, Gabriela Makulyte, Jean-Michel Flaman, Nadine Martin, David Bernard","doi":"10.1083/jcb.202401112","DOIUrl":"10.1083/jcb.202401112","url":null,"abstract":"<p><p>During aging and in some contexts, like embryonic development, wound healing, and diseases such as cancer, senescent cells accumulate and play a key role in different pathophysiological functions. A long-held belief was that cellular senescence decreased normal cell functions, given the loss of proliferation of senescent cells. This view radically changed following the discovery of the senescence-associated secretory phenotype (SASP), factors released by senescent cells into their microenvironment. There is now accumulating evidence that cellular senescence also promotes gain-of-function effects by establishing, reinforcing, or changing cell identity, which can have a beneficial or deleterious impact on pathophysiology. These effects may involve both proliferation arrest and autocrine SASP production, although they largely remain to be defined. Here, we provide a historical overview of the first studies on senescence and an insight into emerging trends regarding the effects of senescence on cell identity.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.8,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11169915/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141305987","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Eukaryotic ribosomal proteins contain extended regions essential for translation coordination. Dedicated chaperones stabilize the associated ribosomal proteins. We identified Bcp1 as the chaperone of uL14 in Saccharomyces cerevisiae. Rkm1, the lysine methyltransferase of uL14, forms a ternary complex with Bcp1 and uL14 to protect uL14. Rkm1 is transported with uL14 by importins to the nucleus, and Bcp1 disassembles Rkm1 and importin from uL14 simultaneously in a RanGTP-independent manner. Molecular docking, guided by crosslinking mass spectrometry and validated by a low-resolution cryo-EM map, reveals the correlation between Bcp1, Rkm1, and uL14, demonstrating the protection model. In addition, the ternary complex also serves as a surveillance point, whereas incorrect uL14 is retained on Rkm1 and prevented from loading to the pre-60S ribosomal subunits. This study reveals the molecular mechanism of how uL14 is protected and quality checked by serial steps to ensure its safe delivery from the cytoplasm until its incorporation into the 60S ribosomal subunit.
{"title":"Dual protection by Bcp1 and Rkm1 ensures incorporation of uL14 into pre-60S ribosomal subunits.","authors":"Min-Chi Yeh, Ning-Hsiang Hsu, Hao-Yu Chu, Cheng-Han Yang, Pang-Hung Hsu, Chi-Chi Chou, Jing-Ting Shie, Wei-Ming Lee, Meng-Chiao Ho, Kai-Yin Lo","doi":"10.1083/jcb.202306117","DOIUrl":"10.1083/jcb.202306117","url":null,"abstract":"<p><p>Eukaryotic ribosomal proteins contain extended regions essential for translation coordination. Dedicated chaperones stabilize the associated ribosomal proteins. We identified Bcp1 as the chaperone of uL14 in Saccharomyces cerevisiae. Rkm1, the lysine methyltransferase of uL14, forms a ternary complex with Bcp1 and uL14 to protect uL14. Rkm1 is transported with uL14 by importins to the nucleus, and Bcp1 disassembles Rkm1 and importin from uL14 simultaneously in a RanGTP-independent manner. Molecular docking, guided by crosslinking mass spectrometry and validated by a low-resolution cryo-EM map, reveals the correlation between Bcp1, Rkm1, and uL14, demonstrating the protection model. In addition, the ternary complex also serves as a surveillance point, whereas incorrect uL14 is retained on Rkm1 and prevented from loading to the pre-60S ribosomal subunits. This study reveals the molecular mechanism of how uL14 is protected and quality checked by serial steps to ensure its safe delivery from the cytoplasm until its incorporation into the 60S ribosomal subunit.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.4,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11248248/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141616497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Microtubules are dynamic polymers that interconvert between phases of growth and shrinkage, yet they provide structural stability to cells. Growth involves hydrolysis of GTP-tubulin to GDP-tubulin, which releases energy that is stored within the microtubule lattice and destabilizes it; a GTP cap at microtubule ends is thought to prevent GDP subunits from rapidly dissociating and causing catastrophe. Here, using in vitro reconstitution assays, we show that GDP-tubulin, usually considered inactive, can itself assemble into microtubules, preferentially at the minus end, and promote persistent growth. GDP-tubulin-assembled microtubules are highly stable, displaying no detectable spontaneous shrinkage. Strikingly, islands of GDP-tubulin within dynamic microtubules stop shrinkage events and promote rescues. Microtubules thus possess an intrinsic capacity for stability, independent of accessory proteins. This finding provides novel mechanisms to explain microtubule dynamics.
微管是一种动态聚合物,可在生长和收缩两个阶段之间相互转换,但却能为细胞提供结构稳定性。生长过程中,GTP-微管蛋白水解为 GDP-微管蛋白,释放出储存在微管晶格中的能量,从而破坏微管晶格的稳定性;微管末端的 GTP 盖被认为能防止 GDP 亚基迅速解离并导致灾难。在这里,我们利用体外重组实验表明,通常被认为是无活性的 GDP-微管蛋白本身可以组装成微管,优先组装在负端,并促进持续生长。GDP-微管蛋白组装的微管高度稳定,不会出现可检测到的自发收缩。令人吃惊的是,动态微管中的 GDP-微管蛋白岛能阻止收缩事件并促进挽救。因此,微管具有内在的稳定性,不受附属蛋白的影响。这一发现为解释微管动力学提供了新的机制。
{"title":"Stable GDP-tubulin islands rescue dynamic microtubules.","authors":"Nassiba Bagdadi, Juliette Wu, Julie Delaroche, Laurence Serre, Christian Delphin, Manon De Andrade, Marion Carcel, Homaira Nawabi, Benoît Pinson, Claire Vérin, Yohann Couté, Sylvie Gory-Fauré, Annie Andrieux, Virginie Stoppin-Mellet, Isabelle Arnal","doi":"10.1083/jcb.202307074","DOIUrl":"10.1083/jcb.202307074","url":null,"abstract":"<p><p>Microtubules are dynamic polymers that interconvert between phases of growth and shrinkage, yet they provide structural stability to cells. Growth involves hydrolysis of GTP-tubulin to GDP-tubulin, which releases energy that is stored within the microtubule lattice and destabilizes it; a GTP cap at microtubule ends is thought to prevent GDP subunits from rapidly dissociating and causing catastrophe. Here, using in vitro reconstitution assays, we show that GDP-tubulin, usually considered inactive, can itself assemble into microtubules, preferentially at the minus end, and promote persistent growth. GDP-tubulin-assembled microtubules are highly stable, displaying no detectable spontaneous shrinkage. Strikingly, islands of GDP-tubulin within dynamic microtubules stop shrinkage events and promote rescues. Microtubules thus possess an intrinsic capacity for stability, independent of accessory proteins. This finding provides novel mechanisms to explain microtubule dynamics.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11101955/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140957646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-05Epub Date: 2024-07-03DOI: 10.1083/jcb.202404013
Vivek Malhotra
Export of secretory cargoes from the endoplasmic reticulum (ER) requires COPII proteins, which were first identified for their ability to coat small vesicles that bud from the ER. Recent data indicate that COPII proteins can also organize into a collar at the necks of tubules, as well as phase-separate into liquid-like condensates. Thus, COPII assemblies seem to be tailored to accommodate variations in the size and quantities of cargo secreted.
从内质网(ER)导出分泌货物需要 COPII 蛋白,人们最初发现 COPII 蛋白能够包裹从 ER 萌发的小囊泡。最近的数据表明,COPII 蛋白还能在小管的颈部组织成环,以及相分离成液体状凝聚体。因此,COPII 的组装似乎是量身定制的,以适应分泌货物的大小和数量的变化。
{"title":"Tailored assemblies of COPII proteins in secretion.","authors":"Vivek Malhotra","doi":"10.1083/jcb.202404013","DOIUrl":"10.1083/jcb.202404013","url":null,"abstract":"<p><p>Export of secretory cargoes from the endoplasmic reticulum (ER) requires COPII proteins, which were first identified for their ability to coat small vesicles that bud from the ER. Recent data indicate that COPII proteins can also organize into a collar at the necks of tubules, as well as phase-separate into liquid-like condensates. Thus, COPII assemblies seem to be tailored to accommodate variations in the size and quantities of cargo secreted.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.4,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11222725/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141492063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-05Epub Date: 2024-06-12DOI: 10.1083/jcb.202402144
Anja Göder, Chrystelle Antoinat Maric, Michael D Rainey, Aisling O'Connor, Chiara Cazzaniga, Daniel Shamavu, Jean-Charles Cadoret, Corrado Santocanale
CDC7 kinase is crucial for DNA replication initiation and is involved in fork processing and replication stress response. Human CDC7 requires the binding of either DBF4 or DRF1 for its activity. However, it is unclear whether the two regulatory subunits target CDC7 to a specific set of substrates, thus having different biological functions, or if they act redundantly. Using genome editing technology, we generated isogenic cell lines deficient in either DBF4 or DRF1: these cells are viable but present signs of genomic instability, indicating that both can independently support CDC7 for bulk DNA replication. Nonetheless, DBF4-deficient cells show altered replication efficiency, partial deficiency in MCM helicase phosphorylation, and alterations in the replication timing of discrete genomic regions. Notably, we find that CDC7 function at replication forks is entirely dependent on DBF4 and not on DRF1. Thus, DBF4 is the primary regulator of CDC7 activity, mediating most of its functions in unperturbed DNA replication and upon replication interference.
{"title":"DBF4, not DRF1, is the crucial regulator of CDC7 kinase at replication forks.","authors":"Anja Göder, Chrystelle Antoinat Maric, Michael D Rainey, Aisling O'Connor, Chiara Cazzaniga, Daniel Shamavu, Jean-Charles Cadoret, Corrado Santocanale","doi":"10.1083/jcb.202402144","DOIUrl":"10.1083/jcb.202402144","url":null,"abstract":"<p><p>CDC7 kinase is crucial for DNA replication initiation and is involved in fork processing and replication stress response. Human CDC7 requires the binding of either DBF4 or DRF1 for its activity. However, it is unclear whether the two regulatory subunits target CDC7 to a specific set of substrates, thus having different biological functions, or if they act redundantly. Using genome editing technology, we generated isogenic cell lines deficient in either DBF4 or DRF1: these cells are viable but present signs of genomic instability, indicating that both can independently support CDC7 for bulk DNA replication. Nonetheless, DBF4-deficient cells show altered replication efficiency, partial deficiency in MCM helicase phosphorylation, and alterations in the replication timing of discrete genomic regions. Notably, we find that CDC7 function at replication forks is entirely dependent on DBF4 and not on DRF1. Thus, DBF4 is the primary regulator of CDC7 activity, mediating most of its functions in unperturbed DNA replication and upon replication interference.</p>","PeriodicalId":15211,"journal":{"name":"Journal of Cell Biology","volume":"223 8","pages":""},"PeriodicalIF":7.8,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11169917/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141305986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}