Ribonuclease Activity of Dis3 Is Required for Mitotic Progression and Provides a Possible Link between Heterochromatin and Kinetochore Function

BACKGROUND: Cellular RNA metabolism has a broad range of functional aspects in cell growth and division, but its role in chromosome segregation during mitosis is only poorly understood. The Dis3 ribonuclease is a key component of the RNA-processing exosome complex. Previous isolation of the dis3-54 cold-sensitive mutant of fission yeast Schizosaccharomyces pombe suggested that Dis3 is also required for correct chromosome segregation. METHODOLOGY/PRINCIPAL FINDINGS: We show here that the progression of mitosis is arrested in dis3-54, and that segregation of the chromosomes is blocked by activation of the mitotic checkpoint control. This block is dependent on the Mad2 checkpoint protein. Double mutant and inhibitor analyses revealed that Dis3 is required for correct kinetochore formation and function, and that this activity is monitored by the Mad2 checkpoint. Dis3 is a member of the highly conserved RNase II family and is known to be an essential subunit of the exosome complex. The dis3-54 mutation was found to alter the RNaseII domain of Dis3, which caused a reduction in ribonuclease activity in vitro. This was associated with loss of silencing of an ura4(+) reporter gene inserted into the outer repeats (otr) and central core (cnt and imr) regions of the centromere. On the other hand, centromeric siRNA maturation and formation of the RITS RNAi effector complex was normal in the dis3-54 mutant. Micrococcal nuclease assay also suggested the overall chromatin structure of the centromere was not affected in dis3-54 mutant. CONCLUSIONS/SIGNIFICANCE: RNase activity of Dis3, a core subunit of exosome, was found to be required for proper kinetochore formation and establishment of kinetochore-microtubule interactions. Moreover, Dis3 was suggested to contribute to kinetochore formation through an involvement in heterochromatic silencing at both outer centromeric repeats and within the central core region. This activity is likely monitored by the mitotic checkpoint, and distinct from that of RNAi-mediated heterochromatin formation directly targeting outer centromeric repeats

PELAGIC COPEPODA IN THE BERING SEA AND THE NORTHWESTERN NORTH PACIFIC WITH SPECIAL REFERENCE TO THEIR VERTICAL DISTRIBUTION

II. Acknowledgement.............................................. III. General structure of hydrography................................ IV. Samplings of plankton.........................................

Zooplankton community in the cove of Cumberland Bay, South Georgia, in the southern summer from January to February 1973

Zooplankton were collected from the littoral water of South Georgia during the period from late January to late February 1973. Ten species of pelagic copepods were identified, of which Calanus acutus, C. simillimus, Drepanopus forcipatus and Oithona frigida were the main constituents. Most of copepods are known as Subantarctic or Antarctic species. Drepanopus forcipatus was the most numerically important species in the littoral water of South Georgia. Numerical abundance of copepods was observed on 1-4 and 19-20 February. Copepod nauplii and the pelagic larvae of benthic worms gave the evidence of active production during the period of sampling. Serial surface samplings showed that Calanus acutus, C. simillimus and Drepanopus forcipatus swarmed around the water surface at night

Copepods collected along 13゜E longitude of the Antarctic Ocean in the 1973 summer

Zooplankton samplings were conducted at 8 stations in the Indian sector of the Antarctic Ocean along 13°E from 27 February to 3 March in 1973 by the 14th Japanese Antarctic Research Expedition. Vertical hauls from 200m to the surface with a Norpac net (45cm in diameter, 0.33mm mesh openings) were carried out. Copepoda occupied more than 80% of the total individual numbers of zooplankton at all stations. The species composition and abundance of copepods were investigated. A total of 15 species except for Oncaeidae were recorded. Calanus propinquus, Calanoides acutus, Ctenocalanus vanus and Oithona similis were numerically important components. Especially C. propinquus, C. acutus and C. vanus occurred abundantly at three stations between 60°S and 63°S and O. similis was abundant near 56°S and 62°S. Other eleven species, Calanus simillimus, Rhincalanus gigas, Clausocalanus laticeps, Euchirella rostromagna, Euchaeta antarctica, Racovitzanus antarcticus, Scolecithricella glacialis, Metridia lucens, Metridia gerlachei, Heterorhabdus austrinus and Haloptilus oxycephalus were small in numbers

Copepods collected along 33.5゜E longitude of the Antarctic Ocean in the 1976 summer

Zooplankton samplings were conducted at 6 stations along 33.5°E in the Indian sector of the Antarctic Ocean from 25 February to 2 March in 1976 by the 17th Japanese Antarctic Research Expedition. Vertical hauls from a depth of 200m to the surface with a Norpac net (45cm in diameter, 0.33mm mesh openings) were carried out. Copepoda occupied more than 85% of the total individual numbers of zooplankton at all stations. The species composition and abundance of copepods were investigated. A total of 18 species except for Oncaeidae were identified. Calanus propinquus, Calanoides acutus, Rhincalanus gigas, Ctenocalanus vanus, Scolecithricella glacialis and Oithona similis were found commonly at almost all stations. Miclocalanus pygmaeus, Lucicutia sp., Haloptilus ocellatus, Haloptilus oxycephalus and Metridia gerlachei occurred south of 60°S and Calanus simillimus, Clausocalanus laticeps, Metridia lucens and Oithona frigida occurred north of 60°S. Euchaeta antarctica, Racovitzanus antarcticus and Heterorhabdus austrinus occurred sporadically and/or in small number