Neural network based tomographic approach to detect earthquake-related ionospheric anomalies

A tomographic approach is used to investigate the fine structure of electron density in the ionosphere. In the present paper, the Residual Minimization Training Neural Network (RMTNN) method is selected as the ionospheric tomography with which to investigate the detailed structure that may be associated with earthquakes. The 2007 Southern Sumatra earthquake (<i>M</i> = 8.5) was selected because significant decreases in the Total Electron Content (TEC) have been confirmed by GPS and global ionosphere map (GIM) analyses. The results of the RMTNN approach are consistent with those of TEC approaches. With respect to the analyzed earthquake, we observed significant decreases at heights of 250–400 km, especially at 330 km. However, the height that yields the maximum electron density does not change. In the obtained structures, the regions of decrease are located on the southwest and southeast sides of the Integrated Electron Content (IEC) (altitudes in the range of 400–550 km) and on the southern side of the IEC (altitudes in the range of 250–400 km). The global tendency is that the decreased region expands to the east with increasing altitude and concentrates in the Southern hemisphere over the epicenter. These results indicate that the RMTNN method is applicable to the estimation of ionospheric electron density

CENP-C Is Involved in Chromosome Segregation, Mitotic Checkpoint Function, and Kinetochore Assembly

CENP-C is a conserved inner kinetochore component. To understand the precise roles of CENP-C in the kinetochore, we created a cell line with a conditional knockout of CENP-C with the tetracycline-inducible system in which the target protein is inactivated at the level of transcription. We found that CENP-C inactivation causes mitotic delay. However, observations of living cells showed that CENP-C-knockout cells progressed to the next cell cycle without normal cell division after mitotic delay. Interphase cells with two nuclei before subsequent cell death were sometimes observed. We also found that ∼60% of CENP-C–deficient cells had no Mad2 signals even after treatment with nocodazole, suggesting that lack of CENP-C impairs the Mad2 spindle checkpoint pathway. We also observed significant reductions in the signal intensities of Mis12 complex proteins at centromeres in CENP-C–deficient cells. CENP-C signals were also weak in interphase nuclei but not in mitotic chromosomes of cells with a knockout of CENP-K, a member of CENP-H complex proteins. These results suggest that centromere localization of CENP-C in interphase nuclei occurs upstream of localization of the Mis12 complex and downstream of localization of the CENP-H complex

Molecular architecture of a kinetochore–microtubule attachment site

Kinetochore attachment to spindle microtubule plus-ends is necessary for accurate chromosome segregation during cell division in all eukaryotes. The centromeric DNA of each chromosome is linked to microtubule plus-ends by eight structural-protein complexes1–9. Knowing the copy number of each of these complexes at one kinetochore–microtubule attachment site is necessary to understand the molecular architecture of the complex, and to elucidate the mechanisms underlying kinetochore function. We have counted, with molecular accuracy, the number of structural protein complexes in a single kinetochore–microtubule attachment using quantitative fluorescence microscopy of GFP-tagged kinetochore proteins in the budding yeast Saccharomyces cerevisiae. We find that relative to the two Cse4p molecules in the centromeric histone1, the copy number ranges from one or two for inner kinetochore proteins such as Mif2p2, to 16 for the DAM–DASH complex8,9 at the kinetochore–microtubule interface. These counts allow us to visualize the overall arrangement of a kinetochore–microtubule attachment. As most of the budding yeast kinetochore proteins have homologues in higher eukaryotes, including humans, this molecular arrangement is likely to be replicated in more complex kinetochores that have multiple microtubule attachments

The CENP-A NAC/CAD kinetochore complex controls chromosome congression and spindle bipolarity

Kinetochores are complex protein machines that link chromosomes to spindle microtubules and contain a structural core composed of two conserved protein–protein interaction networks: the well-characterized KMN (KNL1/MIND/NDC80) and the recently identified CENP-A NAC/CAD. Here we show that the CENP-A NAC/CAD subunits can be assigned to one of two different functional classes; depletion of Class I proteins (Mcm21RCENP−O and Fta1RCENP−L) causes a failure in bipolar spindle assembly. In contrast, depletion of Class II proteins (CENP-H, Chl4RCENP−N, CENP-I and Sim4RCENP−K) prevents binding of Class I proteins and causes chromosome congression defects, but does not perturb spindle formation. Co-depletion of Class I and Class II proteins restores spindle bipolarity, suggesting that Class I proteins regulate or counteract the function of Class II proteins. We also demonstrate that CENP-A NAC/CAD and KMN regulate kinetochore–microtubule attachments independently, even though CENP-A NAC/CAD can modulate NDC80 levels at kinetochores. Based on our results, we propose that the cooperative action of CENP-A NAC/CAD subunits and the KMN network drives efficient chromosome segregation and bipolar spindle assembly during mitosis