Positioning and assembly of division machinery in fission yeast

Ph.DDOCTOR OF PHILOSOPH

Assembly of normal actomyosin rings in the absence of Mid1p and cortical nodes in fission yeast

Cytokinesis in many eukaryotes depends on the function of an actomyosin contractile ring. The mechanisms regulating assembly and positioning of this ring are not fully understood. The fission yeast Schizosaccharomyces pombe divides using an actomyosin ring and is an attractive organism for the study of cytokinesis. Recent studies in S. pombe (Wu, J.Q., V. Sirotkin, D.R. Kovar, M. Lord, C.C. Beltzner, J.R. Kuhn, and T.D. Pollard. 2006. J. Cell Biol. 174:391–402; Vavylonis, D., J.Q. Wu, S. Hao, B. O'Shaughnessy, and T.D. Pollard. 2008. Science. 319:97–100) have suggested that the assembly of the actomyosin ring is initiated from a series of cortical nodes containing several components of this ring. These studies have proposed that actomyosin interactions bring together the cortical nodes to form a compacted ring structure. In this study, we test this model in cells that are unable to assemble cortical nodes. Although the cortical nodes play a role in the timing of ring assembly, we find that they are dispensable for the assembly of orthogonal actomyosin rings. Thus, a mechanism that is independent of cortical nodes is sufficient for the assembly of normal actomyosin rings

In Vitro Contraction of Cytokinetic Ring Depends on Myosin II but not on Actin Dynamics

10.1038/ncb2781Nature Cell Biology157853-859NCBI

Assembly of microtubules and actomyosin rings in the absence of nuclei and spindle pole bodies revealed by a novel genetic method

The nucleus and the centrosomes (spindle pole bodies; SPBs in yeast) are believed to play key roles in the organization of various cellular structures, such as the actomyosin ring and microtubules. The ability to generate cells lacking nuclei and centrosomes (SPBs) is key to the elucidation of the role of these structures in various cellular processes.Here we describe a genetic method, using the Schizosaccharomyces pombe cdc16-116 mutant, to reliably and efficiently generate fission yeast cells lacking nuclei and SPBs. We use this approach to show that the assembly of microtubules does not require nuclear associated microtubule organizing centers and SPBs. We also show that actomyosin rings can assemble albeit inefficiently in the absence of nuclei and SPBs.We conclude that key cytoskeletal elements can be assembled in the absence of nuclei and SPBs. In addition, the approach we describe, taken together with physical approaches such as centrifugation, should facilitate the investigation of the role of the nucleus and SPBs in the assembly and inheritance of various cellular structures and organelles

Potassium Application Alleviated Negative Effects of Soil Waterlogging Stress on Photosynthesis and Dry Biomass in Cotton

Soil waterlogging is one of the most serious abiotic stresses on plant growth and crop productivity. In this study, two potassium application levels (0 and 150 kg K2O hm−2) with three types of soil waterlogging treatments (0 d, 3 d and 6 d) were established during cotton flowering and boll-forming stages. The results showed that soil waterlogging markedly reduced RWC (relative water content), gas exchange parameters and cotton biomass. However, potassium application considerably improved the aforementioned parameters. Specifically, 3 d soil waterlogging with potassium increased Pn (net photosynthetic rate), Gs (stomatal conductance), Ci (intercellular CO2 concentration) and Tr (transpiration rate) by 4.55%, 27.27%, 5.74% and 3.82%, respectively, compared with 3 d soil waterlogging under no potassium, while the abscission rate reduced by 2.96%. Additionally, the number of bolls and fruit nodes under 6 d soil waterlogging with potassium increased by 16.17% and 4.38%, compared with 6 d soil waterlogging under no potassium. Therefore, it was concluded that regardless of 3 d or 6 d soil waterlogging, potassium application alleviated the negative effects of waterlogging by regulating the plant water status, photosynthetic capacity and plant growth in cotton. These results are expected to provide theoretical references and practical applications for cotton production to mitigate the damage of soil waterlogging

Detecting Snowfall Events over Mountainous Areas Using Optical Imagery

Snowfall over mountainous areas not only has important implications on the water cycle and the Earth’s radiation balance, but also causes potentially hazardous weather. However, snowfall detection remains one of the most difficult problems in modern hydrometeorology. We present a method for detecting snowfall events from optical satellite data for seasonal snow in mountainous areas. The proposed methodology is based on identifying expanded snow cover or suddenly declined snow grain size using time series images, from which it is possible to detect the location and time of snowfall events. The methodology was tested with Moderate Resolution Imaging Spectroradiometer (MODIS) daily radiance data for an entire hydrologic year from July 2014 to June 2015 in the mountainous area of the Manas River Basin, Northwest China. The study evaluated the recordings of precipitation events at eighteen meteorological stations in the study area prove the effectiveness of the proposed method, showing that there was more liquid precipitation in the second and third quarter, and more solid precipitation in the first and fourth quarter

Hsp90 Protein in Fission Yeast Swo1p and UCS Protein Rng3p Facilitate Myosin II Assembly and Function

The F-actin-based molecular motor myosin II is involved in a variety of cellular processes such as muscle contraction, cell motility, and cytokinesis. In recent years, a family of myosin II-specific cochaperones of the UCS family has been identified from work with yeasts, fungi, worms, and humans. Biochemical analyses have shown that a complex of Hsp90 and the Caenorhabditis elegans UCS domain protein UNC-45 prevent myosin head aggregation, thereby allowing it to assume a proper structure. Here we demonstrate that a temperature-sensitive mutant of the fission yeast Hsp90 (Swo1p), swo1-w1, is defective in actomyosin ring assembly at the restrictive temperature. Two alleles of swo1, swo1-w1 and swo1-26, showed synthetic lethality with a specific mutant allele of the fission yeast type II myosin head, myo2-E1, but not with two other mutant alleles of myo2 or with mutations affecting 14 other genes important for cytokinesis. swo1-w1 also showed a strong genetic interaction with rng3-65, a gene encoding a mutation in the fission yeast UCS domain protein Rng3p, which has previously been shown to be important for myosin II assembly. A similar deleterious effect was found when myo2-E1, swo1-w1, and rng3-65 were pharmacologically treated with geldanamycin to partially inhibit Hsp90 function. Interestingly, Swo1p-green fluorescent protein is detected at the improperly assembled actomyosin rings in myo2-E1 but not in a wild-type strain. Yeast two-hybrid and coimmunoprecipitation analyses verified interactions between Rng3p and the myosin head domain as well as interactions between Rng3p and Swo1p. Our analyses of Myo2p, Swo1p, and the UCS domain protein Rng3p establish that Swo1p and Rng3p collaborate in vivo to modulate myosin II function