Continental flood basalts derived from the hydrous mantle transition zone

It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can potentially account for the chemical diversity of many continental flood basalts

Spermatogenesis-Specific Features of the Meiotic Program in Caenorhabditis elegans

In most sexually reproducing organisms, the fundamental process of meiosis is implemented concurrently with two differentiation programs that occur at different rates and generate distinct cell types, sperm and oocytes. However, little is known about how the meiotic program is influenced by such contrasting developmental programs. Here we present a detailed timeline of late meiotic prophase during spermatogenesis in Caenorhabditis elegans using cytological and molecular landmarks to interrelate changes in chromosome dynamics with germ cell cellularization, spindle formation, and cell cycle transitions. This analysis expands our understanding C. elegans spermatogenesis, as it identifies multiple spermatogenesis-specific features of the meiotic program and provides a framework for comparative studies. Post-pachytene chromatin of spermatocytes is distinct from that of oocytes in both composition and morphology. Strikingly, C. elegans spermatogenesis includes a previously undescribed karyosome stage, a common but poorly understood feature of meiosis in many organisms. We find that karyosome formation, in which chromosomes form a constricted mass within an intact nuclear envelope, follows desynapsis, involves a global down-regulation of transcription, and may support the sequential activation of multiple kinases that prepare spermatocytes for meiotic divisions. In spermatocytes, the presence of centrioles alters both the relative timing of meiotic spindle assembly and its ultimate structure. These microtubule differences are accompanied by differences in kinetochores, which connect microtubules to chromosomes. The sperm-specific features of meiosis revealed here illuminate how the underlying molecular machinery required for meiosis is differentially regulated in each sex

The elegans of spindle assembly

The Caenorhabditis elegans one-cell embryo is a powerful system in which to study microtubule organization because this large cell assembles both meiotic and mitotic spindles within the same cytoplasm over the course of 1 h in a stereotypical manner. The fertilized oocyte assembles two consecutive acentrosomal meiotic spindles that function to reduce the replicated maternal diploid set of chromosomes to a single-copy haploid set. The resulting maternal DNA then unites with the paternal DNA to form a zygotic diploid complement, around which a centrosome-based mitotic spindle forms. The early C. elegans embryo is amenable to live-cell imaging and electron tomography, permitting a detailed structural comparison of the meiotic and mitotic modes of spindle assembly

Lateral and End-On Kinetochore Attachments Are Coordinated to Achieve Bi-orientation in Drosophila Oocytes

In oocytes, where centrosomes are absent, the chromosomes direct the assembly of a bipolar spindle. Interactions between chromosomes and microtubules are essential for both spindle formation and chromosome segregation, but the nature and function of these interactions is not clear. We have examined oocytes lacking two kinetochore proteins, NDC80 and SPC105R, and a centromere-associated motor protein, CENP-E, to characterize the impact of kinetochore-microtubule attachments on spindle assembly and chromosome segregation in Drosophila oocytes. We found that the initiation of spindle assembly results from chromosome-microtubule interactions that are kinetochore-independent. Stabilization of the spindle, however, depends on both central spindle and kinetochore components. This stabilization coincides with changes in kinetochore-microtubule attachments and bi-orientation of homologs. We propose that the bi-orientation process begins with the kinetochores moving laterally along central spindle microtubules towards their minus ends. This movement depends on SPC105R, can occur in the absence of NDC80, and is antagonized by plus-end directed forces from the CENP-E motor. End-on kinetochore-microtubule attachments that depend on NDC80 are required to stabilize bi-orientation of homologs. A surprising finding was that SPC105R but not NDC80 is required for co-orientation of sister centromeres at meiosis I. Together, these results demonstrate that, in oocytes, kinetochore-dependent and -independent chromosome-microtubule attachments work together to promote the accurate segregation of chromosomes

Environmental Control on Biotic Development in Siberia (Verkhoyansk Region) and Neighbouring Areas During Permian-Triassic Large Igneous Province Activity

We propose an updated ammonoid zonation for the Permian-Triassic boundary succession (the lower Nekuchan Formation) in the Verkhoyansk region of Siberia: (1) Otoceras concavum zone (uppermost Changhsingian); (2) Otoceras boreale zone (lowermost Induan); (3) Tompophiceras morpheous zone (lower Induan); and (4) Wordieoceras decipiens zone (lower Induan). The Tompophiceras pascoei zone, previously defined between the Otoceras boreale and Tompophiceras morpheous zones, is removed in our scheme. Instead of this the Tompophiceras pascoei epibole zone is proposed for the lower part of the Tompophiceras morpheous zone. New and previously published nitrogen isotope records are interpreted as responses to climatic fluctuations in the middle to higher palaeolatitudes of Northeastern Asia and these suggest a relatively cool climatic regime for the Boreal Superrealm; however the trend towards warming across the Permian-Triassic boundary transition is also seen. The evolutionary development and geographical differentiation of otoceratid ammonoids and associated groups are considered. It is likely that the Boreal Superrealm was their main refugium, where otocerid, dzhulfitid and some other ammonoids survived the major biotic crisis at the end of the Permian. The similarity of ontogenetic development of suture lines of Otoceras woodwardi Griesbach and O. boreale Spath gives some grounds for suggesting a monophyletic origin of the genus Otoceras, having bipolar distribution

Does 'Political Bias' Undermine the Korea Investment Corporation?

Based on “in-depth study”, the aim of the chapter is to analyze Korea Investment Corporation (KIC), a non-commodity Sovereign Wealth Fund, in order to investigate its investment strategies over the time (2005-2012) and evaluate any form of ‘political bias’. Our results suggest that KIC pursues financial objectives, aiming to maximize the portfolio risk/return relationship, as it manages foreign excess reserves of those managed by Bank of Korea. We also argue that a form of ‘internal political bias’ affects investment process, as most of the financial resources are managed in-house. Overall, we support the hypothesis that in Korea Investment Corporation both financial and political objectives coexist

A novel chromosome segregation mechanism during female meiosis

In a wide range of eukaryotes, chromosome segregation occurs through anaphase A, in which chromosomes move toward stationary spindle poles, anaphase B, in which chromosomes move at the same velocity as outwardly moving spindle poles, or both. In contrast, Caenorhabditis elegans female meiotic spindles initially shorten in the pole-to-pole axis such that spindle poles contact the outer kinetochore before the start of anaphase chromosome separation. Once the spindle pole-to-kinetochore contact has been made, the homologues of a 4-μm-long bivalent begin to separate. The spindle shortens an additional 0.5 μm until the chromosomes are embedded in the spindle poles. Chromosomes then separate at the same velocity as the spindle poles in an anaphase B–like movement. We conclude that the majority of meiotic chromosome movement is caused by shortening of the spindle to bring poles in contact with the chromosomes, followed by separation of chromosome-bound poles by outward sliding