The decline and fate of an iron-induced subarctic phytoplankton bloom

Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters. However, the fate of the carbon fixed by these blooms, and how efficiently it is exported into the ocean's interior, remains largely unknown. Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska. The bloom terminated on day 18, following the depletion of iron and then silicic acid, after which mixed-layer particulate organic carbon (POC) concentrations declined over six days. Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21, yet increased POC export was not evident until day 24. Only a small proportion of the mixed-layer POC was intercepted by the traps, with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing. The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past, and also for proposed geo-engineering schemes to increase oceanic carbon sequestration.     

Pummerer-type Functionalization of Aryl and Alkenyl Selenoxides

Heteroatom-stabilized carbenium ions have been widely recognized as potential electrophilic reagents. However, in contrast with the extensive works on thionium ion series, the highly labile character of selenoxide functionalities has caused serious limitation in the synthetic use in spite of their wide potentiality as synthetic equivalents of electrophilic selonium ions. In this paper, novel generation of selonium ions and the synthetic uses of the species for Pummerer-type α-functionalization and for cycloaddition by using the novel dienophilic behavior of π-conjugated selonium cations.     

Green chemistry: biodiesel made with sugar catalyst

The production of diesel from vegetable oil calls for an efficient solid catalyst to make the process fully ecologically friendly. Here we describe the preparation of such a catalyst from common, inexpensive sugars. This high-performance catalyst, which consists of stable sulphonated amorphous carbon, is recyclable and its activity markedly exceeds that of other solid acid catalysts tested for 'biodiesel' production.     

Genome sequence of the endocellular bacterial symbiont of aphids Buchnera sp. APS

Almost all aphid species (Homoptera, Insecta) have 60-80 huge cells called bacteriocytes, within which are round-shaped bacteria that are designated Buchnera. These bacteria are maternally transmitted to eggs and embryos through host generations, and the mutualism between the host and the bacteria is so obligate that neither can reproduce independently. Buchnera is a close relative of Escherichia coli, but it contains more than 100 genomic copies per cell, and its genome size is only a seventh of that of E. coli. Here we report the complete genome sequence of Buchnera sp. strain APS, which is composed of one 640,681-base-pair chromosome and two small plasmids. There are genes for the biosyntheses of amino acids essential for the hosts in the genome, but those for non-essential amino acids are missing, indicating complementarity and syntrophy between the host and the symbiont. In addition, Buchnera lacks genes for the biosynthesis of cell-surface components, including lipopolysaccharides and phospholipids, regulator genes and genes involved in defence of the cell. These results indicate that Buchnera is completely symbiotic and viable only in its limited niche, the bacteriocyte.     

Giant magneto-elastic coupling in multiferroic hexagonal manganites

The motion of atoms in a solid always responds to cooling or heating in a way that is consistent with the symmetry of the given space group of the solid to which they belong. When the atoms move, the electronic structure of the solid changes, leading to different physical properties. Therefore, the determination of where atoms are and what atoms do is a cornerstone of modern solid-state physics. However, experimental observations of atomic displacements measured as a function of temperature are very rare, because those displacements are, in almost all cases, exceedingly small. Here we show, using a combination of diffraction techniques, that the hexagonal manganites RMnO3 (where R is a rare-earth element) undergo an isostructural transition with exceptionally large atomic displacements: two orders of magnitude larger than those seen in any other magnetic material, resulting in an unusually strong magneto-elastic coupling. We follow the exact atomic displacements of all the atoms in the unit cell as a function of temperature and find consistency with theoretical predictions based on group theories. We argue that this gigantic magneto-elastic coupling in RMnO3 holds the key to the recently observed magneto-electric phenomenon in this intriguing class of materials.     

Self-formation of functional adenohypophysis in three-dimensional culture

The adenohypophysis (anterior pituitary) is a major centre for systemic hormones. At present, no efficient stem-cell culture for its generation is available, partly because of insufficient knowledge about how the pituitary primordium (Rathke's pouch) is induced in the embryonic head ectoderm. Here we report efficient self-formation of three-dimensional adenohypophysis tissues in an aggregate culture of mouse embryonic stem (ES) cells. ES cells were stimulated to differentiate into non-neural head ectoderm and hypothalamic neuroectoderm in adjacent layers within the aggregate, and treated with hedgehog signalling. Self-organization of Rathke's-pouch-like three-dimensional structures occurred at the interface of these two epithelia, as seen in vivo, and various endocrine cells including corticotrophs and somatotrophs were subsequently produced. The corticotrophs efficiently secreted adrenocorticotropic hormone in response to corticotrophin releasing hormone and, when grafted in vivo, these cells rescued the systemic glucocorticoid level in hypopituitary mice. Thus, functional anterior pituitary tissue self-forms in ES cell culture, recapitulating local tissue interactions.     

Cdc42 and mDia3 regulate microtubule attachment to kinetochores

During mitosis, the mitotic spindle, a bipolar structure composed of microtubules (MTs) and associated motor proteins, segregates sister chromatids to daughter cells. Initially some MTs emanating from one centrosome attach to the kinetochore at the centromere of one of the duplicated chromosomes. This attachment allows rapid poleward movement of the bound chromosome. Subsequent attachment of the sister kinetochore to MTs growing from the other centrosome results in the bi-orientation of the chromosome, in which interactions between kinetochores and the plus ends of MTs are formed and stabilized. These processes ensure alignment of chromosomes during metaphase and their correct segregation during anaphase. Although many proteins constituting the kinetochore have been identified and extensively studied, the signalling responsible for MT capture and stabilization is unclear. Small GTPases of the Rho family regulate cell morphogenesis by organizing the actin cytoskeleton and regulating MT alignment and stabilization. We now show that one member of this family, Cdc42, and its effector, mDia3, regulate MT attachment to kinetochores.     

7-Dehydrosterols in prothoracic glands of the silkworm,Bombyx mori

Summary Sterol analysis of prothoracic glands of the silkworm,Bombyx mori revealed the presence of 7-dehydrocampesterol and 7-dehydrositosterol together with 7-dehydrocholesterol. It was also found that the amounts of these 7-dehydrosterols were increased in proportion to the ecdysone titer.     

Radixin deficiency causes conjugated hyperbilirubinemia with loss of Mrp2 from bile canalicular membranes

The ezrin-radixin-moesin (ERM) family of proteins crosslink actin filaments and integral membrane proteins. Radixin (encoded by Rdx) is the dominant ERM protein in the liver of wildtype mice and is concentrated at bile canalicular membranes (BCMs). Here we show that Rdx(-/-) mice are normal at birth, but their serum concentrations of conjugated bilirubin begin to increase gradually around 4 weeks, and they show mild liver injury after 8 weeks. This phenotype is similar to human conjugated hyperbilirubinemia in Dubin-Johnson syndrome, which is caused by mutations in the multidrug resistance protein 2 (MRP2, gene symbol ABCC2), although this syndrome is not associated with overt liver injury. In wildtype mice, Mrp2 concentrates at BCMs to secrete conjugated bilirubin into bile. In the BCMs of Rdx(-/-) mice, Mrp2 is decreased compared with other BCM proteins such as dipeptidyl peptidase IV (CD26) and P-glycoproteins. In vitro binding studies show that radixin associates directly with the carboxy-terminal cytoplasmic domain of human MRP2. These findings indicate that radixin is required for secretion of conjugated bilirubin through its support of Mrp2 localization at BCMs.