Chlorophyll a concentration of phytoplankton during a cruise of the 51st Japanese Antarctic Research Expedition in 2009-2010

Measurements of phytoplankton chlorophyll a concentration in seawater at depths less than 200 m were made in the Indian sector of the Southern Ocean during the 51st Japanese Antarctic Research Expedition (JARE) in the austral summer of 2009–2010. This expedition was the first cruise of the new icebreaker Shirase

Role of the Schizosaccharomyces pombe F-box DNA helicase in processing recombination intermediates.

In an effort to identify novel genes involved in recombination repair, we isolated fission yeast Schizosaccharomyces pombe mutants sensitive to methyl methanesulfonate (MMS) and a synthetic lethal with rad2. A gene that complements such mutations was isolated from the S. pombe genomic library, and subsequent analysis identified it as the fbh1 gene encoding the F-box DNA helicase, which is conserved in mammals but not conserved in Saccharomyces cerevisiae. An fbh1 deletion mutant is moderately sensitive to UV, MMS, and ¿ rays. The rhp51 (RAD51 ortholog) mutation is epistatic to fbh1. fbh1 is essential for viability in stationary-phase cells and in the absence of either Srs2 or Rqh1 DNA helicase. In each case, lethality is suppressed by deletion of the recombination gene rhp57. These results suggested that fbh1 acts downstream of rhp51 and rhp57. Following UV irradiation or entry into the stationary phase, nuclear chromosomal domains of the fbh1¿ mutant shrank, and accumulation of some recombination intermediates was suggested by pulsed-field gel electrophoresis. Focus formation of Fbh1 protein was induced by treatment that damages DNA. Thus, the F-box DNA helicase appears to process toxic recombination intermediates, the formation of which is dependent on the function of Rhp51

Schizosaccharomyces pombe Cds1 regulates homologous recombination at stalled replication forks through the phosphorylation of recombination protein Rad60

The Schizosaccharomyces pombe rad60 gene is essential for cell growth and is involved in repairing DNA double-strand breaks. Rad60 physically interacts with, and is functionally related to, the structural maintenance of chromosomes 5 and 6 protein complex (Smc5/6). Rad60 is phosphorylated in response to hydroxyurea (HU)-induced DNA replication arrest in a Cds1Chk2- dependent manner. Rad60 localizes in nucleus in unchallenged cells, but becomes diffused throughout the cell in response to HU. To understand the role of Rad60 phosphorylation, we mutated the putative phosphorylation target motifs of Cds1Chk2 and have identified two Cds1Chk2 target residues responsible for Rad60 dispersal in response to HU. We show that the phosphorylationdefective rad60 mutation partially suppresses HU sensitivity and the elevated recombination frequency of smc6-X. Our data suggest that Rad60 phosphorylation is required to regulate homologous recombination at stalled replication forks, probably by regulating Smc5/6. Supplementary material available online at http://jcs.biologists.org/cgi/content/full/122/20/3638/DC

Composition and Architecture of the Schizosaccharomyces pombe Rad18 (Smc5-6) Complex

The rad18 gene of Schizosaccharomyces pombe is an essential gene that is involved in several different DNA repair processes. Rad18 (Smc6) is a member of the structural maintenance of chromosomes (SMC) family and, together with its SMC partner Spr18 (Smc5), forms the core of a high-molecular-weight complex. We show here that both S. pombe and human Smc5 and -6 interact through their hinge domains and that four independent temperature-sensitive mutants of Rad18 (Smc6) are all mutated at the same glycine residue in the hinge region. This mutation abolishes the interactions between the hinge regions of Rad18 (Smc6) and Spr18 (Smc5), as does mutation of a conserved glycine in the hinge region of Spr18 (Smc5). We purified the Smc5-6 complex from S. pombe and identified four non-SMC components, Nse1, Nse2, Nse3, and Rad62. Nse3 is a novel protein which is related to the mammalian MAGE protein family, many members of which are specifically expressed in cancer tissue. In initial steps to understand the architecture of the complex, we identified two subcomplexes containing Rad18-Spr18-Nse2 and Nse1-Nse3-Rad62. The subcomplexes are probably bridged by a weaker interaction between Nse2 and Nse3

Early development and neurogenesis of Temnopleurus reevesii

Sea urchins are model non-chordate deuterostomes, and studying the nervous system of their embryos can aid in the understanding of the universal mechanisms of neurogenesis. However, despite the long history of sea urchin embryology research, the molecular mechanisms of their neurogenesis have not been well investigated, in part because neurons appear relatively late during embryogenesis. In this study, we used the species Temnopleurus reevesii as a new sea urchin model and investigated the detail of its development and neurogenesis during early embryogenesis. We found that the embryos of T. reevesii were tolerant of high temperatures and could be cultured successfully at 15–30°C during early embryogenesis. At 30°C, the embryos developed rapidly enough that the neurons appeared at just after 24 h. This is faster than the development of other model urchins, such as Hemicentrotus pulcherrimus or Strongylocentrotus purpuratus. In addition, the body of the embryo was highly transparent, allowing the details of the neural network to be easily captured by ordinary epifluorescent and confocal microscopy without any additional treatments. Because of its rapid development and high transparency during embryogenesis, T. reevesii may be a suitable sea urchin model for studying neurogenesis. Moreover, the males and females are easily distinguishable, and the style of early cleavages is intriguingly unusual, suggesting that this sea urchin might be a good candidate for addressing not only neurology but also cell and developmental biology