抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

The important advances and current trends in the stereocontrolled ring-opening polymerisation of lactide are discussed in this tutorial review. Microstructures, structural characterisation methods and the properties of stereoregular poly(lactide)s are examined. The application of metal-based catalysts dominates this area although simple anionic polymerisation and organocatalytic routes that demonstrate control of the polymer tacticity are discussed.

Stereocontrolled ring-opening polymerisation of lactide

Large igneous provinces (LIPs) are intraplate magmatic events, involving volumes of mainly mafic magma upwards of 100,000 km3, and often above 1 million km3. They are linked to continental break-up, global environmental catastrophes, regional uplift and a variety of ore deposit types. In this up-to-date, fascinating book, leading expert Richard E. Ernst explores all aspects of LIPs, beginning by introducing their definition and essential characteristics. Topics covered include continental and oceanic LIPs; their origins, structures, and geochemistry; geological and environmental effects; association with silicic, carbonatite and kimberlite magmatism; and analogues of LIPs in the Archean, and on other planets. The book concludes with an assessment of LIPs' influence on natural resources such as mineral deposits, petroleum and aquifers. This is a one-stop resource for researchers and graduate students in a wide range of disciplines, including tectonics, igneous petrology, geochemistry, geophysics, Earth history, and planetary geology, and for mining industry professionals.

Large Igneous Provinces

The review summarizes recent developments in the preparation and use of new initiators for the ring opening polymerization of lactide. The review compares different classes of initiator including metal complexes, classed according to their group in the periodic table, and carbon‐based initiators/organocatalysts. Emphasis is placed on the polymerization kinetics and the control exhibited by the different types of initiators. Where useful properties, such as high rates or stereocontrol, have been observed a more detailed examination of the initiator is provided. A further focus of the review is initiators displaying low toxicity and biocompatibility.

Biocompatible Initiators for Lactide Polymerization

There have been five Mass Extinction events in the history of Earth's biodiversity, all caused by dramatic but natural phenomena. It has been claimed that the Sixth Mass Extinction may be underway, this time caused entirely by humans. Although considerable evidence indicates that there is a biodiversity crisis of increasing extinctions and plummeting abundances, some do not accept that this amounts to a Sixth Mass Extinction. Often, they use the IUCN Red List to support their stance, arguing that the rate of species loss does not differ from the background rate. However, the Red List is heavily biased: almost all birds and mammals but only a minute fraction of invertebrates have been evaluated against conservation criteria. Incorporating estimates of the true number of invertebrate extinctions leads to the conclusion that the rate vastly exceeds the background rate and that we may indeed be witnessing the start of the Sixth Mass Extinction. As an example, we focus on molluscs, the second largest phylum in numbers of known species, and, extrapolating boldly, estimate that, since around AD 1500, possibly as many as 7.5–13% (150,000–260,000) of all ~2 million known species have already gone extinct, orders of magnitude greater than the 882 (0.04%) on the Red List. We review differences in extinction rates according to realms: marine species face significant threats but, although previous mass extinctions were largely defined by marine invertebrates, there is no evidence that the marine biota has reached the same crisis as the non‐marine biota. Island species have suffered far greater rates than continental ones. Plants face similar conservation biases as do invertebrates, although there are hints they may have suffered lower extinction rates. There are also those who do not deny an extinction crisis but accept it as a new trajectory of evolution, because humans are part of the natural world; some even embrace it, with a desire to manipulate it for human benefit. We take issue with these stances. Humans are the only species able to manipulate the Earth on a grand scale, and they have allowed the current crisis to happen. Despite multiple conservation initiatives at various levels, most are not species oriented (certain charismatic vertebrates excepted) and specific actions to protect every living species individually are simply unfeasible because of the tyranny of numbers. As systematic biologists, we encourage the nurturing of the innate human appreciation of biodiversity, but we reaffirm the message that the biodiversity that makes our world so fascinating, beautiful and functional is vanishing unnoticed at an unprecedented rate. In the face of a mounting crisis, scientists must adopt the practices of preventive archaeology, and collect and document as many species as possible before they disappear. All this depends on reviving the venerable study of natural history and taxonomy. Denying the crisis, simply accepting it and doing nothing, or even embracing it for the ostensible benefit of humanity, are not appropriate options and pave the way for the Earth to continue on its sad trajectory towards a Sixth Mass Extinction.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/brv.12816

The Sixth Mass Extinction: fact, fiction or speculation?

Mass extinctions manifest in Earth’s geologic record were turning points in biotic evolution. We present 40 Ar/ 39 Ar data that establish synchrony between the Cretaceous-Paleogene boundary and associated mass extinctions with the Chicxulub bolide impact to within 32,000 years. Perturbation of the atmospheric carbon cycle at the boundary likely lasted less than 5000 years, exhibiting a recovery time scale two to three orders of magnitude shorter than that of the major ocean basins. Low-diversity mammalian fauna in the western Williston Basin persisted for as little as 20,000 years after the impact. The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress.

/pdf/time-scales-of-critical-events-around-the-cretaceous-1piu0w7mcf.pdf

Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary

Stereoselective Controlled Polymerization of dl-Lactide with [Ti(trisphenolate)O-i-Pr]2 Initiators

Plesiadapiform mammals, as stem primates, are key to understanding the evolutionary and ecological origins of Pan-Primates and Euarchonta. The Purgatoriidae, as the geologically oldest and most pri...

https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.210050

Earliest Palaeocene purgatoriids and the initial radiation of stem primates.

The Whitehorse Group and Quartermaster Formation are extensive red-bed terrestrial sequences representing the final episode of sedimentation in the Palo Duro Basin in north-central Texas, U.S.A. Regionally, these strata record the culmination of a long-term regression sequence beginning in the middle to late Permian. The Whitehorse Group includes beds of abundant laminated to massive red quartz siltstone to fine sandstone and rare dolomite, laminated to massive gypsum, and claystones, as well as diagenetic gypsum. The Quartermaster Formation exhibits a change from nearly equal amounts of thin planar and lenticular fine sandstone and laminated to massive mudstone in its lower half to overlying strata with coarser-grained, cross-bedded sandstones indicative of meandering channels up to 7 m deep and rare overbank mudstones. Paleosols are absent in the Upper Whitehorse Group and only poorly developed in the Quartermaster Formation. Volcanic ash-fall deposits (tuffs) present in uppermost Whitehorse Group and lower Quartermaster Formation strata permit correlation among five stratigraphic sections distributed over ∼150 km and provide geochronologic age information for these rocks. Both the Whitehorse Group and Quartermaster Formation have traditionally been assigned to the late Permian Ochoan (Changhsingian) stage, and workers assumed that the Permian-Triassic boundary is characterized by a regionally significant unconformity. Chemostratigraphic or biostratigraphic evidence for this age assignment, however, have been lacking to date. Single zircon U-Pb CA-TIMS analyses from at least two distinct volcanic ash fall layers in the lower Quartermaster Formation, which were identified and collected from five different localities across the Palo Duro Basin, yield interpreted depositional ages ranging from 252.19 ± 0.30 to 251.74 ± 0.28 Ma. Single zircon U-Pb CA-TIMS analyses of detrital zircons from sandstones located only a few meters beneath the top of the Quartermaster Formation yield a range of dates from Mesoproterozoic (1418 Ma) to Middle Triassic (244.5 Ma; Anisian), the latter of which is interpreted as a maximum depositional age, which is no older than Anisian, thus indicating the Permian-Triassic boundary to lie somewhere within the lower Quartermaster Formation/upper Whitehorse Group succession. Stable carbon isotope data from 180 samples of early-burial dolomicrite cements preserve a chemostratigraphic signal that is similar among sections, with a large ∼−8‰ negative isotope excursion ∼20 m beneath the Whitehorse Group-Quartermaster Formation boundary. This large negative carbon isotope excursion is interpreted to be the same excursion associated with the end-Permian extinction and this is in concert with the new high precision radioisotopic age data presented and the fact that the excursion lies within a normal polarity stratigraphic magnetozone. Dolomite cement δ13C values remain less negative (between about −5 and −8 permil) into the lower part of the Quartermaster Formation before becoming more positive toward the top of the section. This long interval of negative δ13C values in the Quartermaster Formation is interpreted to represent the earliest Triassic (Induan) inception of biotic and ecosystem “recovery.” Oxygen isotope values of dolomicrite cements show a progressive trend toward more positive values through the boundary interval, suggesting substantially warmer conditions around the end-Permian extinction event and a trend toward cooler conditions after the earliest Triassic. Our observations on these strata show that the paleoenvironment and paleoclimate across the Permian-Triassic boundary in western, sub-equatorial Pangea was characterized by depositional systems that were not conducive to plant preservation.

Evidence of a Continuous Continental Permian-Triassic Boundary Section in western Equatorial Pangea, Palo Duro Basin, Northwest Texas, U.S.A.

Retreat of Stephenson Glacier, Heard Island, from Remote Sensing and Field Observations

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