Арагонитовые и кальцитовые жеоды из пещеры Ботовская

В статье описываются необычные вторичные минеральные образования, обнаруженные в Ботовской пещере в Восточной Сибири, которые представляют собой жеоды, выполненные арагонитом, а в отдельных случаях – кальцитом. Приведены два предположения о формирование жеод: за счет стекающих растворов, размывающих рыхлые пещерные отложения и заполняющих образовавшиеся пустоты, в которых затем происходила кристаллизация минералов, и за счет растворения центрального тела сформированных ранее конкреций и последующего отложения арагонита и кальцита в получившейся полости. Впоследствии жеоды были вскрыты при выносе из пещеры большого объема осадков водными потоками. Вследствие особенностей своей морфологии и генезиса данные образования могут рассматриваться как новый тип спелеотем.У статті описуються незвичайні вторинні мінеральні утворення, виявлені у Ботовской печері у Східному Сибіру, якими є жеоди, виповнені арагонітом, а в окремих випадках - кальцитом. Наведені два припущення про формування жеод: за рахунок стікаючих розчинів, що розмивають пухкі печерні відклади і заповнюють порожнини, що утворилися, в яких потім відбувалася кристалізація мінералів, і за рахунок розчинення центрального тіла сформованих раніше конкрецій і подальшого відкладення арагоніту і кальциту у порожнини, що утворилися. Згодом жеоди були розкриті при винесенні з печери великого об'єму відкладень водними потоками. Внаслідок особливостей своєї морфології і генезису ці утворення можуть розглядатися як новий тип спелеотем.The article describes unusual secondary mineral formation found in Botovskaya Cave in Eastern Siberia, which are geodes, lined byaragonite and, in some cases, by calcite. Two assumptions of the geode formation are put forward: 1) at the expense of draining solutions that erode loose sediments and fill formed cavities, where then mineral crystallization occurs; 2) at the expense of dissolution of the central body of concretions formed earlier, followed by precipitation of aragonite and calcite in the cavity formed. Later on, the geodes were uncovered during erosion of large volumes of sediments by water flows. Due to peculiar features of their morphology and genesis, these formations can be regarded as a new type of speleothems

Chemical Genetic Inhibition of Mps1 in Stable Human Cell Lines Reveals Novel Aspects of Mps1 Function in Mitosis

Proper execution of chromosome segregation relies on tight control of attachment of chromosomes to spindle microtubules. This is monitored by the mitotic checkpoint that allows chromosome segregation only when all chromosomes are stably attached. Proper functioning of the attachment and checkpoint processes is thus important to prevent chromosomal instability. Both processes rely on the mitotic kinase Mps1.We present here two cell lines in which endogenous Mps1 has been stably replaced with a mutant kinase (Mps1-as) that is specifically inhibited by bulky PP1 analogs. Mps1 inhibition in these cell lines is highly penetrant and reversible. Timed inhibition during bipolar spindle assembly shows that Mps1 is critical for attachment error-correction and confirms its role in Aurora B regulation. We furthermore show that Mps1 has multiple controls over mitotic checkpoint activity. Mps1 inhibition precludes Mad1 localization to unattached kinetochores but also accelerates mitosis. This acceleration correlates with absence of detectable mitotic checkpoint complex after Mps1 inhibition. Finally, we show that short-term inhibition of Mps1 catalytic activity is sufficient to kill cells.Mps1 is involved in the regulation of multiple key processes that ensure correct chromosome segregation and is a promising target for inhibition in anti-cancer strategies. We report here two cell lines that allow specific and highly penetrant inhibition of Mps1 in a reproducible manner through the use of chemical genetics. Using these cell lines we confirm previously suggested roles for Mps1 activity in mitosis, present evidence for novel functions and examine cell viability after short and prolonged Mps1 inhibition. These cell lines present the best cellular model system to date for investigations into Mps1 biology and the effects of penetrance and duration of Mps1 inhibition on cell viability

Universal Quantitative Kinase Assay Based on Diagonal SCX Chromatography and Stable Isotope Dimethyl Labeling Provides High-definition Kinase Consensus Motifs for PKA and Human Mps1

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Microtubule nucleation from the fibrous corona by LIC1-pericentrin promotes chromosome congression

Error-free chromosome segregation in mitosis and meiosis relies on the assembly of a microtubule-based spindle that interacts with kinetochores to guide chromosomes to the cell equator before segregation in anaphase. Microtubules sprout from nucleation sites such as centrosomes, but kinetochores can also promote microtubule formation. It is unclear, however, how kinetochore-derived microtubules are generated and what their role is in chromosome segregation. Here, we show that the transient outer-kinetochore meshwork known as the fibrous corona serves as an autonomous microtubule nucleation platform. The fibrous corona is essential for the nucleation of kinetochore-derived microtubules, and when dissociated from the core kinetochore, it retains microtubule nucleation capacity. Nucleation relies on a fibrous-corona-bound pool of the LIC1 subunit of the dynein motor complex, which interacts with the γ-tubulin-tethering protein pericentrin (PCNT). PCNT is essential for microtubule nucleation from fibrous coronas, and in centrosome-depleted cells, where nearly all mitotic nucleation occurs at fibrous coronas, chromosome congression is fully dependent on PCNT. We further show that chromosomes in bovine oocytes, which naturally lack centrosomes, have highly expanded fibrous coronas that drive chromosome-derived microtubule nucleation. Preventing fibrous corona expansion in these cells impairs chromosome congression and causes spindle assembly defects. Our results show that fibrous coronas are autonomous microtubule-organizing centers that are important for spindle assembly, which may be especially relevant in acentrosomal cells such as oocytes

The Molecular Basis of Monopolin Recruitment to the Kinetochore

The monopolin complex is a multifunctional molecular crosslinker, which in S. pombe binds and organises mitotic kinetochores to prevent aberrant kinetochore-microtubule interactions. In the budding yeast S. cerevisiae, whose kinetochores bind a single microtubule, the monopolin complex crosslinks and mono-orients sister kinetochores in meiosis I, enabling the biorientation and segregation of homologs. Here, we show that both the monopolin complex subunit Csm1 and its binding site on the kinetochore protein Dsn1 are broadly distributed throughout eukaryotes, suggesting a conserved role in kinetochore organisation and function. We find that budding yeast Csm1 binds two conserved motifs in Dsn1, one (termed Box 1) representing the ancestral, widely conserved monopolin binding motif and a second (termed Box 2-3) with a likely role in enforcing specificity of sister kinetochore crosslinking. We find that Box 1 and Box 2-3 bind the same conserved hydrophobic cavity on Csm1, suggesting competition or handoff between these motifs. Using structure-based mutants, we also find that both Box 1 and Box 2-3 are critical for monopolin function in meiosis. We identify two conserved serine residues in Box 2-3 that are phosphorylated in meiosis and whose mutation to aspartate stabilises Csm1-Dsn1 binding, suggesting that regulated phosphorylation of these residues may play a role in sister kinetochore crosslinking specificity. Overall, our results reveal the monopolin complex as a broadly conserved kinetochore organiser in eukaryotes, which budding yeast have co-opted to mediate sister kinetochore crosslinking through the addition of a second, regulatable monopolin binding interface

Chromosomal Instability by Inefficient Mps1 Auto-Activation Due to a Weakened Mitotic Checkpoint and Lagging Chromosomes

BACKGROUND: Chromosomal instability (CIN), a feature widely shared by cells from solid tumors, is caused by occasional chromosome missegregations during cell division. Two of the causes of CIN are weakened mitotic checkpoint signaling and persistent merotelic attachments that result in lagging chromosomes during anaphase. PRINCIPAL FINDINGS: Here we identify an autophosphorylation event on Mps1 that is required to prevent these two causes of CIN. Mps1 is phosphorylated in mitotic cells on at least 7 residues, 4 of which by autophosphorylation. One of these, T676, resides in the activation loop of the kinase domain and a mutant that cannot be phosphorylated on T676 is less active than wild-type Mps1 but is not kinase-dead. Strikingly, cells in which endogenous Mps1 was replaced with this mutant are viable but missegregate chromosomes frequently. Anaphase is initiated in the presence of misaligned and lagging chromosomes, indicative of a weakened checkpoint and persistent merotelic attachments, respectively. CONCLUSIONS/SIGNIFICANCE: We propose that full activity of Mps1 is essential for maintaining chromosomal stability by allowing resolution of merotelic attachments and to ensure that single kinetochores achieve the strength of checkpoint signaling sufficient to prevent premature anaphase onset and chromosomal instability. To our knowledge, phosphorylation of T676 on Mps1 is the first post-translational modification in human cells of which the absence causes checkpoint weakening and CIN without affecting cell viability

Chromosomal instability by mutations in the novel minor spliceosome component CENATAC

Aneuploidy is the leading cause of miscarriage and congenital birth defects, and a hallmark of cancer. Despite this strong association with human disease, the genetic causes of aneuploidy remain largely unknown. Through exome sequencing of patients with constitutional mosaic aneuploidy, we identified biallelic truncating mutations in CENATAC (CCDC84). We show that CENATAC is a novel component of the minor (U12-dependent) spliceosome that promotes splicing of a specific, rare minor intron subtype. This subtype is characterized by AT-AN splice sites and relatively high basal levels of intron retention. CENATAC depletion or expression of disease mutants resulted in excessive retention of AT-AN minor introns in similar to 100 genes enriched for nucleocytoplasmic transport and cell cycle regulators, and caused chromosome segregation errors. Our findings reveal selectivity in minor intron splicing and suggest a link between minor spliceosome defects and constitutional aneuploidy in humans.Peer reviewe

Conditional targeting of MAD1 to kinetochores is sufficient to reactivate the spindle assembly checkpoint in metaphase

Fidelity of chromosome segregation is monitored by the spindle assembly checkpoint (SAC). Key components of the SAC include MAD1, MAD2, BUB1, BUB3, BUBR1, and MPS1. These proteins accumulate on kinetochores in early prometaphase but are displaced when chromosomes attach to microtubules and/or biorient on the mitotic spindle. As a result, stable attachment of the final chromosome satisfies the SAC, permitting activation of the anaphase promoting complex/cyclosome (APC/C) and subsequent anaphase onset. SAC satisfaction is reversible, however, as addition of taxol during metaphase stops cyclin B1 degradation by the APC/C. We now show that targeting MAD1 to kinetochores during metaphase is sufficient to reestablish SAC activity after initial silencing. Using rapamycin-induced heterodimerization of FKBP-MAD1 to FRB-MIS12 and live monitoring of cyclin B1 degradation, we show that timed relocalization of MAD1 during metaphase can stop cyclin B1 degradation without affecting chromosome-spindle attachments. APC/C inhibition represented true SAC reactivation, as FKBP-MAD1 required an intact MAD2-interaction motif and MPS1 activity to accomplish this. Our data show that MAD1 kinetochore localization dictates SAC activity and imply that SAC regulatory mechanisms downstream of MAD1 remain functional in metaphase. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00412-014-0458-9) contains supplementary material, which is available to authorized users

Germline mutations in the spindle assembly checkpoint genes BUB1 and BUB3 are infrequent in familial colorectal cancer and polyposis

Germline mutations in BUB1 and BUB3 have been reported to increase the risk of developing colorectal cancer (CRC) at young age, in presence of variegated aneuploidy and reminiscent dysmorphic traits of mosaic variegated aneuploidy syndrome. We performed a mutational analysis of BUB1 and BUB3 in 456 uncharacterized mismatch repair-proficient hereditary non-polyposis CRC families and 88 polyposis cases. Four novel or rare germline variants, one splice-site and three missense, were identified in four families. Neither variegated aneuploidy nor dysmorphic traits were observed in carriers. Evident functional effects in the heterozygous form were observed for c.1965-1G>A, but not for c.2296G>A (p.E766K), in spite of the positive co-segregation in the family. BUB1 c.2473C>T (p.P825S) and BUB3 c.77C>T (p.T26I) remained as variants of uncertain significance. As of today, the rarity of functionally relevant mutations identified in familial and/or early onset series does not support the inclusion of BUB1 and BUB3 testing in routine genetic diagnostics of familial CRC