23 research outputs found
The cytoskeleton in cell-autonomous immunity: structural determinants of host defence
Host cells use antimicrobial proteins, pathogen-restrictive compartmentalization and cell death in their defence against intracellular pathogens. Recent work has revealed that four components of the cytoskeleton — actin, microtubules, intermediate filaments and septins, which are well known for their roles in cell division, shape and movement — have important functions in innate immunity and cellular self-defence. Investigations using cellular and animal models have shown that these cytoskeletal proteins are crucial for sensing bacteria and for mobilizing effector mechanisms to eliminate them. In this Review, we highlight the emerging roles of the cytoskeleton as a structural determinant of cell-autonomous host defence
Increased expression of keratinase and other peptidases by Candida parapsilosis mutants
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Holocene moisture changes in western China, Central Asia, inferred from stalagmites
Central Asia lies at the convergence between the Mediterranean and Asian monsoon climates, and there is a complex interaction between the westerlies with the monsoon to form the climate of that region and its variability. The region is highly vulnerable to changes in rainfall, highlighting the need to understand the underlying controls. We present a stalagmite-based δ18O record from Kesang Cave in western China, using MC-ICP-MS U-series dating and stable isotope analysis. Stalagmite calcite δ18O largely documents changes in the δ18O of precipitation. δ18O in stalagmites was low during the early and middle Holocene (10.0–3.0 ka BP), and shifted to higher values between 3.0 and 2.0 ka BP. After 2.0 ka BP, δ18O fluctuates with distinct centennial-scale variations. Drawing from results of state-of-the-art atmospheric general circulation model simulations for the preindustrial period and 9 ka BP, we propose that changes in moisture source regions and the wetter climate both contributed to the isotopic depletion of precipitation during the early and middle Holocene. Multiple records from surrounding regions indicate a generally wetter climate during the early and mid- Holocene, supporting our interpretation on the speleothem δ18O. Changes in precipitation seasonality do not appear to be a viable explanation for the observed changes, nor increased penetration of monsoonal moisture to the study site. We speculate that the climatic regime shifted around 3.0–2.0 ka BP towards a drier climate, resulting in temperature having dominant control on precipitation δ18O. The demise of three settlements around 500AD at the margin of Tarim Basin coincided with a period of decreased precipitation and increased temperature that likely affected local water resources, underscoring the potential impact of climate on human habitation in this region
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Role of seasonal transitions and westerly jets in East Asian paleoclimate
The summer rainfall climate of East Asia underwent large and abrupt changes during past climates, in response to precessional forcing, glacial-interglacial cycles as well as abrupt changes to the North Atlantic during the Last Glacial. However, current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity, and do not account for the known complexity in the seasonal evolution of East Asian rainfall, which exhibits sharp transition from the Spring regime to the Meiyu, and then again from the Meiyu to the Summer regime. We explore the interpretation that East Asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes. Following previous suggestions we focus on role of the westerly jet over Asia, namely that its latitude relative to Tibet is critical in determining the stepwise transitions in East Asian rainfall seasons. In support of this linkage, we show from observational data that the interannual co-variation of June (July-August) rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the Meiyu (Summer), and with more northward-shifted westerlies for earlier transitions.We similarly suggest that East Asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions, in particular the transition of the jet from south of the Plateau to the north that determines the seasonal transition from Spring rains to the Meiyu. In an extreme scenario - which we speculate the climate system tended towards during stadial (cold) phases of D/O stadials and periods of low Northern Hemisphere summer insolation - the jet does not jump north of the Plateau, essentially keeping East Asia in prolonged Spring conditions.We argue that this hypothesis provides a viable explanation for a key paleoproxy signature of D/O stadials over East Asia, namely the heavier mean δ18O of precipitation as recorded in speleothem records. The southward jet position prevents the low-level monsoonal flow - which is isotopically light - from penetrating into the interior of East Asia; as such, precipitation there will be heavier, consistent with speleothem records. This hypothesis can also explain other key evidences of East Asian paleoclimate changes, in particular the occurrence of dusty conditions during North Atlantic stadials, and the southward migration of the Holocene optimal rainfall
Role of seasonal transitions and westerly jets in East Asianpaleoclimate
The summer rainfall climate of East Asia underwent large and abrupt changes during past climates, in
response to precessional forcing, glacialeinterglacial cycles as well as abrupt changes to the North
Atlantic during the Last Glacial. However, current interpretations of said changes are typically formulated
in terms of modulation of summer monsoon intensity, and do not account for the known complexity in
the seasonal evolution of East Asian rainfall, which exhibits sharp transition from the Spring regime to
the Meiyu, and then again from the Meiyu to the Summer regime.
We explore the interpretation that East Asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes. Following previous suggestions we focus on role of the westerly
jet over Asia, namely that its latitude relative to Tibet is critical in determining the stepwise transitions in
East Asian rainfall seasons. In support of this linkage, we show from observational data that the interannual co-variation of June (JulyeAugust) rainfall and upper tropospheric zonal winds show properties
consistent with an altered timing of the transition to the Meiyu (Summer), and with more northwardshifted westerlies for earlier transitions.
We similarly suggest that East Asian paleoclimate changes resulted from an altered timing in the
northward evolution of the jet and hence the seasonal transitions, in particular the transition of the jet
from south of the Plateau to the north that determines the seasonal transition from Spring rains to the
Meiyu. In an extreme scenario e which we speculate the climate system tended towards during stadial
(cold) phases of D/O stadials and periods of low Northern Hemisphere summer insolation e the jet does
not jump north of the Plateau, essentially keeping East Asia in prolonged Spring conditions.
We argue that this hypothesis provides a viable explanation for a key paleoproxy signature of D/O
stadials over East Asia, namely the heavier mean d18O of precipitation as recorded in speleothem records.
The southward jet position prevents the low-level monsoonal flow e which is isotopically light e from
penetrating into the interior of East Asia; as such, precipitation there will be heavier, consistent with
speleothem records. This hypothesis can also explain other key evidences of East Asian paleoclimate
changes, in particular the occurrence of dusty conditions during North Atlantic stadials, and the
southward migration of the Holocene optimal rainfall