The axial element protein HTP-3 promotes cohesin loading and meiotic axis assembly in C. elegans to implement the meiotic program of chromosome segregation

Centromeres are chromosomal regions that serve as sites for kinetochore formation and microtubule attachment, processes that are essential for chromosome segregation during mitosis. Centromeres are almost universally defined by the histone variant CENP-A. In the holocentric nematode C. elegans, CENP-A deposition depends on the loading factor KNL-2. Depletion of either CENP-A or KNL-2 results in defects in centromere maintenance, chromosome condensation and kinetochore formation, leading to chromosome segregation failure. Here, we show that KNL-2 is phosphorylated by CDK-1, and that mutation of three C-terminal phosphorylation sites causes chromosome segregation defects and an increase in embryonic lethality. In strains expressing phosphodeficient KNL-2, CENP-A and kinetochore proteins are properly localised, indicating that the role of KNL-2 in centromere maintenance is not affected. Instead, the mutant embryos exhibit reduced mitotic levels of condensin II on chromosomes and significant chromosome condensation impairment. Our findings separate the functions of KNL-2 in CENP-A loading and chromosome condensation and demonstrate that KNL-2 phosphorylation regulates the cooperation between centromeric regions and the condensation machinery in C. elegans.

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Repurposing of Synaptonemal Complex Proteins for Kinetochores in Kinetoplastida

10.1101/2021.02.06.430040 ◽

2021 ◽

Cited By ~ 1

Author(s):

Eelco C. Tromer ◽

Thomas A. Wemyss ◽

Ross F. Waller ◽

Bungo Akiyoshi

Keyword(s):

Gene Family ◽

Synaptonemal Complex ◽

Chromosome Segregation ◽

Homology Detection ◽

Homologous Chromosomes ◽

Chromosome Synapsis ◽

Core Set ◽

History Of ◽

Macromolecular Protein ◽

Axial Element

AbstractChromosome segregation in eukaryotes is driven by a macromolecular protein complex called the kinetochore that connects centromeric DNA to microtubules of the spindle apparatus. Kinetochores in well-studied model eukaryotes consist of a core set of proteins that are broadly conserved among distant eukaryotic phyla. In contrast, unicellular flagellates of the class Kinetoplastida have a unique set of kinetochore components. The evolutionary origin and history of these kinetochores remains unknown. Here, we report evidence of homology between three kinetoplastid kinetochore proteins KKT16–18 and axial element components of the synaptonemal complex, such as the SYCP2:SYCP3 multimers found in vertebrates. The synaptonemal complex is a zipper-like structure that assembles between homologous chromosomes during meiosis to promote recombination. Using a sensitive homology detection protocol, we identify divergent orthologues of SYCP2:SYCP3 in most eukaryotic supergroups including other experimentally established axial element components, such as Red1 and Rec10 in budding and fission yeast, and the ASY3:ASY4 multimers in land plants. These searches also identify KKT16–18 as part of this rapidly evolving protein family. The widespread presence of the SYCP2-3 gene family in extant eukaryotes suggests that the synaptonemal complex was likely present in the last eukaryotic common ancestor. We found at least twelve independent duplications of the SYCP2-3 gene family throughout the eukaryotic tree of life, providing opportunities for new functional complexes to arise, including KKT16–18 in Trypanosoma brucei. We propose that kinetoplastids evolved their unique kinetochore system by repurposing meiotic components of the chromosome synapsis and homologous recombination machinery that were already present in early eukaryotes.

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Male meiotic spindle features that efficiently segregate paired and lagging chromosomes

10.1101/737494 ◽

2019 ◽

Author(s):

Gunar Fabig ◽

Robert Kiewisz ◽

Norbert Lindow ◽

James A. Powers ◽

Vanessa Cota ◽

...

Keyword(s):

Chromosome Segregation ◽

Chromosome Pairing ◽

Electron Tomography ◽

Male Meiosis ◽

Meiotic Spindle ◽

Sperm Production ◽

C Elegans ◽

Anaphase Onset ◽

Unpaired Chromosome ◽

Anaphase B

AbstractChromosome segregation during male meiosis is tailored to rapidly generate multitudes of sperm. Little, however, is known about the mechanisms that efficiently segregate chromosomes to produce sperm. Using live imaging in Caenorhabditis elegans, we find that spermatocytes exhibit simultaneous pole-to-chromosome shortening (anaphase A) and pole-to-pole elongation (anaphase B). Electron tomography unexpectedly revealed that spermatocyte anaphase A does not stem from kinetochore microtubule shortening. Instead, movement is driven by changes in distance between chromosomes, microtubules, and centrosomes upon tension release at anaphase onset. We also find that the lagging X chromosome, a distinctive feature of anaphase I in C. elegans males, is due to lack of chromosome pairing. The unpaired chromosome remains tethered to centrosomes by continuously lengthening kinetochore microtubules which are under tension, suggesting a ‘tug of war’ that can reliably resolve chromosome lagging. Overall, we define features that partition both paired and lagging chromosomes for optimal sperm production.

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Condensin DC spreads linearly and bidirectionally from recruitment sites to create loop-anchored TADs in C. elegans

10.1101/2021.03.23.436694 ◽

2021 ◽

Cited By ~ 1

Author(s):

David Sebastian Jimenez ◽

Jun Kim ◽

Bhavana Ragipani ◽

Bo Zhang ◽

Lena Annika Street ◽

...

Keyword(s):

Chromosome Segregation ◽

X Chromosome ◽

Molecular Motors ◽

Sequence Motif ◽

X Chromosomes ◽

C Elegans ◽

Eukaryotic Chromosome ◽

Multiple Copies

AbstractCondensins are molecular motors that compact DNA for chromosome segregation and gene regulation. In vitro experiments have begun to elucidate the mechanics of condensin function but how condensin loading and translocation along DNA controls eukaryotic chromosome structure in vivo remains poorly understood. To address this question, we took advantage of a specialized condensin, which organizes the 3D conformation of X chromosomes to mediate dosage compensation (DC) in C. elegans. Condensin DC is recruited and spreads from a small number of recruitment elements on the X chromosome (rex). We found that ectopic insertion of rex sites on an autosome leads to bidirectional spreading of the complex over hundreds of kilobases. On the X chromosome, strong rex sites contain multiple copies of a 12-bp sequence motif and act as TAD borders. Inserting a strong rex and ectopically recruiting the complex on the X chromosome or an autosome creates a loop-anchored TAD. Unlike the CTCF system, which controls TAD formation by cohesin, direction of the 12-bp motif does not control the specificity of loops. In an X;V fusion chromosome, condensin DC linearly spreads into V and increases 3D DNA contacts, but fails to form TADs in the absence of rex sites. Finally, we provide in vivo evidence for the loop extrusion hypothesis by targeting multiple dCas9-Suntag complexes to an X chromosome repeat region. Consistent with linear translocation along DNA, condensin DC accumulates at the block site. Together, our results support a model whereby strong rex sites act as insulation elements through recruitment and bidirectional spreading of condensin DC molecules and form loop-anchored TADs.

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Intertwined Functions of Separase and Caspase in Cell Division and Programmed Cell Death

10.1101/653584 ◽

2019 ◽

Author(s):

Pan-Young Jeong ◽

Ashish Kumar ◽

Pradeep Joshi ◽

Joel H. Rothman

Keyword(s):

Cell Proliferation ◽

Cell Division ◽

Chromosome Segregation ◽

Meiotic Chromosome ◽

Cysteine Proteases ◽

Embryonic Lethality ◽

Substrate Specificities ◽

C Elegans ◽

Cell Suicide ◽

Chromosome Disjunction

AbstractTimely sister chromatid separation, promoted by separase, is essential for faithful chromosome segregation. Separase is a member of the CD clan of cysteine proteases, which also includes the pro-apoptotic enzymes known as caspases. We report that the C. elegans separase SEP-1, primarily known for its role in cell division, is required for apoptosis when the predominant pro-apoptotic caspase CED-3 is compromised. Loss of SEP-1 results in extra surviving cells in a weak ced-3(−) mutant, and suppresses the embryonic lethality of a mutant defective for the apoptotic suppressor ced-9/Bcl-2. We also report apparent non-apoptotic roles for CED-3 in promoting germ cell proliferation and germline meiotic chromosome disjunction and the normal rate of embryonic development. Moreover, loss of the soma-specific (CSP-3) and germline-specific (CSP-2) caspase inhibitors results in CED-3-dependent suppression of embryonic lethality and meiotic chromosome non-disjunction respectively, when separase function is compromised. Thus, while caspases and separases have evolved different substrate specificities associated with their specialized functions in apoptosis and cell division respectively, they appear to have retained the residual ability to participate in both processes, supporting the view that co-option of components in cell division may have led to the innovation of programmed cell suicide early in metazoan evolution.

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The MAP kinase pathway coordinates crossover designation with disassembly of synaptonemal complex proteins during meiosis

eLife ◽

10.7554/elife.12039 ◽

2016 ◽

Vol 5 ◽

Cited By ~ 11

Author(s):

Saravanapriah Nadarajan ◽

Firaz Mohideen ◽

Yonatan B Tzur ◽

Nuria Ferrandiz ◽

Oliver Crawley ◽

...

Keyword(s):

Map Kinase ◽

Synaptonemal Complex ◽

Chromosome Segregation ◽

Meiotic Chromosome ◽

Late Pachytene ◽

C Elegans ◽

Map Kinase Pathway ◽

Rho Gef ◽

Kinase Signaling Pathway ◽

Kinase Pathway

Asymmetric disassembly of the synaptonemal complex (SC) is crucial for proper meiotic chromosome segregation. However, the signaling mechanisms that directly regulate this process are poorly understood. Here we show that the mammalian Rho GEF homolog, ECT-2, functions through the conserved RAS/ERK MAP kinase signaling pathway in the C. elegans germline to regulate the disassembly of SC proteins. We find that SYP-2, a SC central region component, is a potential target for MPK-1-mediated phosphorylation and that constitutively phosphorylated SYP-2 impairs the disassembly of SC proteins from chromosomal domains referred to as the long arms of the bivalents. Inactivation of MAP kinase at late pachytene is critical for timely disassembly of the SC proteins from the long arms, and is dependent on the crossover (CO) promoting factors ZHP-3/RNF212/Zip3 and COSA-1/CNTD1. We propose that the conserved MAP kinase pathway coordinates CO designation with the disassembly of SC proteins to ensure accurate chromosome segregation.

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A highly conserved centrosomal kinase, AIR-1, is required for accurate cell cycle progression and segregation of developmental factors in Caenorhabditis elegans embryos

Development ◽

10.1242/dev.125.22.4391 ◽

1998 ◽

Vol 125 (22) ◽

pp. 4391-4402 ◽

Cited By ~ 9

Author(s):

J.M. Schumacher ◽

N. Ashcroft ◽

P.J. Donovan ◽

A. Golden

Keyword(s):

Chromosome Segregation ◽

Mitotic Spindle ◽

Cell Cycle Progression ◽

Cycle Progression ◽

Centrosomal Protein ◽

C Elegans ◽

Developmental Factors ◽

Centrosome Separation ◽

Spindle Dynamics ◽

Bipolar Spindles

S. cerevisiae Ipl1, Drosophila Aurora, and the mammalian centrosomal protein IAK-1 define a new subfamily of serine/threonine kinases that regulate chromosome segregation and mitotic spindle dynamics. Mutations in ipl1 and aurora result in the generation of severely aneuploid cells and, in the case of aurora, monopolar spindles arising from a failure in centrosome separation. Here we show that a related, essential protein from C. elegans, AIR-1 (Aurora/Ipl1 related), is localized to mitotic centrosomes. Disruption of AIR-1 protein expression in C. elegans embryos results in severe aneuploidy and embryonic lethality. Unlike aurora mutants, this aneuploidy does not arise from a failure in centrosome separation. Bipolar spindles are formed in the absence of AIR-1, but they appear to be disorganized and are nucleated by abnormal-looking centrosomes. In addition to its requirement during mitosis, AIR-1 may regulate microtubule-based developmental processes as well. Our data suggests AIR-1 plays a role in P-granule segregation and the association of the germline factor PIE-1 with centrosomes.

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CSC-1

The Journal of Cell Biology ◽

10.1083/jcb.200207117 ◽

2003 ◽

Vol 161 (2) ◽

pp. 229-236 ◽

Cited By ~ 67

Author(s):

Alper Romano ◽

Annika Guse ◽

Ivica Krascenicova ◽

Heinke Schnabel ◽

Ralf Schnabel ◽

...

Keyword(s):

Caenorhabditis Elegans ◽

Genetic Analysis ◽

Chromosome Segregation ◽

Kinase Activity ◽

Aurora B ◽

Aurora B Kinase ◽

C Elegans ◽

The Individual

The Aurora B kinase complex is a critical regulator of chromosome segregation and cytokinesis. In Caenorhabditis elegans, AIR-2 (Aurora B) function requires ICP-1 (Incenp) and BIR-1 (Survivin). In various systems, Aurora B binds to orthologues of these proteins. Through genetic analysis, we have identified a new subunit of the Aurora B kinase complex, CSC-1. C. elegans embryos depleted of CSC-1, AIR-2, ICP-1, or BIR-1 have identical phenotypes. CSC-1, BIR-1, and ICP-1 are interdependent for their localization, and all are required for AIR-2 localization. In vitro, CSC-1 binds directly to BIR-1. The CSC-1/BIR-1 complex, but not the individual subunits, associates with ICP-1. CSC-1 associates with ICP-1, BIR-1, and AIR-2 in vivo. ICP-1 dramatically stimulates AIR-2 kinase activity. This activity is not stimulated by CSC-1/BIR-1, suggesting that these two subunits function as targeting subunits for AIR-2 kinase.

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RMD-1, a novel microtubule-associated protein, functions in chromosome segregation in Caenorhabditis elegans

The Journal of Cell Biology ◽

10.1083/jcb.200705108 ◽

2007 ◽

Vol 179 (6) ◽

pp. 1149-1162 ◽

Cited By ~ 18

Author(s):

Kumiko Oishi ◽

Hideyuki Okano ◽

Hitoshi Sawa

Keyword(s):

Caenorhabditis Elegans ◽

Chromosome Segregation ◽

Growth Defect ◽

Aurora B ◽

C Elegans ◽

Spindle Poles ◽

Protein Functions ◽

Microtubule Growth ◽

Mild Defect

For proper chromosome segregation, the sister kinetochores must attach to microtubules extending from the opposite spindle poles. Any errors in microtubule attachment can induce aneuploidy. In this study, we identify a novel conserved Caenorhabditis elegans microtubule-associated protein, regulator of microtubule dynamics 1 (RMD-1), that localizes to spindle microtubules and spindle poles. Depletion of RMD-1 induces severe defects in chromosome segregation, probably through merotelic attachments between microtubules and chromosomes. Although rmd-1 embryos also have a mild defect in microtubule growth, we find that mutants of the microtubule growth regulator XMAP215/ZYG-9 show much weaker segregation defects. This suggests that the microtubule growth defect in rmd-1 embryos does not cause abnormal chromosome segregation. We also see that RMD-1 interacts with aurora B in vitro. Our results suggest that RMD-1 functions in chromosome segregation in C. elegans embryos, possibly through the aurora B–mediated pathway. Human homologues of RMD-1 could also bind microtubules, which would suggest a function for these proteins in chromosome segregation during mitosis in other organisms as well.

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