Mid-anaphase arrest in S. cerevisiae cells eliminated for the function of Cin8 and dynein

S. cerevisiae anaphase spindle elongation is accomplished by the overlapping function of dynein and the kinesin-5 motor proteins, Cin8 and Kip1. Cin8 and dynein are synthetically lethal, yet the arrest phenotypes of cells eliminated for their function had not been identified. We found that at a non-permissive temperature, dyn1Δ cells that carry a temperature-sensitive cin8 – 3 mutation arrest at mid-anaphase with a unique phenotype, which we named TAN (two microtubule asters in one nucleus). These cells enter anaphase, but fail to proceed through the slow phase of anaphase B. At a permissive temperature, dyn1Δ, cin8 – 3 or dyn1Δcin8 – 3 cells exhibit perturbed spindle midzone morphologies, with dyn1Δcin8 – 3 anaphase spindles also being profoundly bent and nonrigid. Sorbitol, which has been suggested to stabilize microtubules, corrects these defects and suppresses the TAN phenotype. We conclude that dynein and Cin8 cooperate in anaphase midzone organization and influence microtubule dynamics, thus enabling progression through the slow phase of anaphase B. Received 10 August 2008; received after revision 22 October 2008; accepted 27 October 2008     

A new species of Orobdella (Hirudinida: Arhynchobdellida: Orobdellidae) from Primorye Territory,Russian Far East

A quadrannulate leech species, Orobdella ghilarovi sp. nov., from Primorye Territory in the southern Russian Far East is described. Phylogenetic analyses using nuclear 18S rRNA, 28S rRNA, histone H3, mitochondrial cytochrome c oxidase subunit I, tRNA^Cys, tRNA^Met, 12S rRNA, tRNA^Val, 16S rRNA, tRNA^Leu and NADH dehydrogenase subunit 1 markers showed that O. ghilarovi forms a fully supported clade with a monophyletic lineage comprising two species, O. kawakatsuorum and O. koikei, inhabiting Hokkaido, Japan. Quadrannulate Orobdella leeches distributed in the southern Primorye Territory have been identified as O. whitmani, which was originally described in Japan; these past records should be amended based on the taxonomic conclusions of this study.

http://zoobank.org/urn:lsid:zoobank.org:pub:8D91AC1C-5868-4F0B-A09D-423F7B50206C     

Three Cdk1 sites in the kinesin-5 Cin8 catalytic domain coordinate motor localization and activity during anaphase

The bipolar kinesin-5 motors perform essential functions in mitotic spindle dynamics. We previously demonstrated that phosphorylation of at least one of the Cdk1 sites in the catalytic domain of the Saccharomyces cerevisiae kinesin-5 Cin8 (S277, T285, S493) regulates its localization to the anaphase spindle. The contribution of these three sites to phospho-regulation of Cin8, as well as the timing of such contributions, remains unknown. Here, we examined the function and spindle localization of phospho-deficient (serine/threonine to alanine) and phospho-mimic (serine/threonine to aspartic acid) Cin8 mutants. In vitro, the three Cdk1 sites undergo phosphorylation by Clb2-Cdk1. In cells, phosphorylation of Cin8 affects two aspects of its localization to the anaphase spindle, translocation from the spindle-pole bodies (SPBs) region to spindle microtubules (MTs) and the midzone, and detachment from the mitotic spindle. We found that phosphorylation of S277 is essential for the translocation of Cin8 from SPBs to spindle MTs and the subsequent detachment from the spindle. Phosphorylation of T285 mainly affects the detachment of Cin8 from spindle MTs during anaphase, while phosphorylation at S493 affects both the translocation of Cin8 from SPBs to the spindle and detachment from the spindle. Only S493 phosphorylation affected the anaphase spindle elongation rate. We conclude that each phosphorylation site plays a unique role in regulating Cin8 functions and postulate a model in which the timing and extent of phosphorylation of the three sites orchestrates the anaphase function of Cin8.     

树木管胞大小对于西伯利亚南部林草交错带森林生长及环境适应性的指示意义

为了研究木质部细胞、树木个体和森林群落3个尺度之间的关联, 在西伯利亚南部以西伯利亚落叶松(Larix sibirica)和欧洲赤松(Pinus sylvestris)为主的3个采样点37个样地, 测量725根树芯的树木年轮宽度, 采用系统随机的方法选择其中195个树芯进行管胞大小的测量和计算。结果表明, 尽管局地环境和树种组成有所不同, 但在树木个体和森林群落两个水平上, 管胞大小与树木径向生长的年际变化显著相关。较小的平均管胞尺寸指示更低的年际生长量和更高的年际生长波动。平均管胞大小对半干旱区针叶林生境湿度和森林生长适应性具有指示作用, 揭示树木通过调节管胞的大小在生长适应与生长安全性二者间的权衡机制。     

刚性沉水植物影响下波浪传播及泥沙悬浮数值模拟

由于植物引起的紊动作用,含刚性植物床面中悬浮泥沙浓度与无植物裸床相比显著增加,而通过平均流速计算底床切应力的传统泥沙模型无法模拟出该现象。因此,在含植物水流水沙运动物理模型试验的基础上,构建了基于Flow–3D的含刚性沉水植物条件下波浪传播的三维数学模型,模拟了植物影响下波浪动力特征和泥沙悬浮过程,同时从紊动能角度修正希尔兹数,对泥沙模块进行了改进。与实测数据相比,该模型可较精确地模拟出植物引起的整体水流流速减小和局部冠层顶部处的流速增大、水体紊动增强以及紊动能在波周期内出现两个峰值的现象。与原始泥沙模块相比,改进的模型考虑了植物尾流紊动对泥沙运动的影响,可提高含植物床面泥沙悬浮模拟的精度。     

Tubulin chaperone E binds microtubules and proteasomes and protects against misfolded protein stress

Mutation of tubulin chaperone E (TBCE) underlies hypoparathyroidism, retardation, and dysmorphism (HRD) syndrome with defective microtubule (MT) cytoskeleton. TBCE/yeast Pac2 comprises CAP-Gly, LRR (leucine-rich region), and UbL (ubiquitin-like) domains. TBCE folds α-tubulin and promotes α/β dimerization. We show that Pac2 functions in MT dynamics: the CAP-Gly domain binds α-tubulin and MTs, and functions in suppression of benomyl sensitivity of pac2Δ mutants. Pac2 binds proteasomes: the LRR binds Rpn1, and the UbL binds Rpn10; the latter interaction mediates Pac2 turnover. The UbL also binds the Skp1-Cdc53-F-box (SCF) ubiquitin ligase complex; these competing interactions for the UbL may impact on MT dynamics. pac2Δ mutants are sensitive to misfolded protein stress. This is suppressed by ectopic PAC2 with both the CAP-Gly and UbL domains being essential. We propose a novel role for Pac2 in the misfolded protein stress response based on its ability to interact with both the MT cytoskeleton and the proteasomes.     

Bidirectional motility of kinesin-5 motor proteins: structural determinants,cumulative functions and physiological roles

Mitotic kinesin-5 bipolar motor proteins perform essential functions in mitotic spindle dynamics by crosslinking and sliding antiparallel microtubules (MTs) apart within the mitotic spindle. Two recent studies have indicated that single molecules of Cin8, the Saccharomyces cerevisiae kinesin-5 homolog, are minus end-directed when moving on single MTs, yet switch directionality under certain experimental conditions (Gerson-Gurwitz et al., EMBO J 30:4942–4954, 2011; Roostalu et al., Science 332:94–99, 2011). This finding was unexpected since the Cin8 catalytic motor domain is located at the N-terminus of the protein, and such kinesins have been previously thought to be exclusively plus end-directed. In addition, the essential intracellular functions of kinesin-5 motors in separating spindle poles during mitosis can only be accomplished by plus end-directed motility during antiparallel sliding of the spindle MTs. Thus, the mechanism and possible physiological role of the minus end-directed motility of kinesin-5 motors remain unclear. Experimental and theoretical studies from several laboratories in recent years have identified additional kinesin-5 motors that are bidirectional, revealed structural determinants that regulate directionality, examined the possible mechanisms involved and have proposed physiological roles for the minus end-directed motility of kinesin-5 motors. Here, we summarize our current understanding of the remarkable ability of certain kinesin-5 motors to switch directionality when moving along MTs.