| 1. |
- Klionsky, Daniel J., et al.
(författare)
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Guidelines for the use and interpretation of assays for monitoring autophagy
- 2012
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Ingår i: Autophagy. - : Informa UK Limited. - 1554-8635 .- 1554-8627. ; 8:4, s. 445-544
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Forskningsöversikt (refereegranskat)abstract
- In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
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| 2. |
- Margold, Martin, et al.
(författare)
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Retreat pattern of the Cordilleran Ice Sheet in central British Columbia at the end of the last glaciation reconstructed from glacial meltwater landforms
- 2013
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 42:4, s. 830-847
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Tidskriftsartikel (refereegranskat)abstract
- The Cordilleran Ice Sheet (CIS) covered much of the mountainous northwestern part of North America at least several times during the Pleistocene. The pattern and timing of its growth and decay are, however, poorly understood. Here, we present a reconstruction of the pattern of ice-sheet retreat in central British Columbia at the end of the last glaciation based on a palaeoglaciological interpretation of ice-marginal meltwater channels, eskers and deltas mapped from satellite imagery and digital elevation models. A consistent spatial pattern of high-elevation (1600-2400m a.s.l.), ice-marginal meltwater channels is evident across central British Columbia. These landforms indicate the presence of ice domes over the Skeena Mountains and the central Coast Mountains early during deglaciation. Ice sourced in the Coast Mountains remained dominant over the southern and east-central parts of the Interior Plateau during deglaciation. Our reconstruction shows a successive westward retreat of the ice margin from the western foot of the Rocky Mountains, accompanied by the formation and rapid evolution of a glacial lake in the upper Fraser River basin. The final stage of deglaciation is characterized by the frontal retreat of ice lobes through the valleys of the Skeena and Omineca Mountains and by the formation of large esker systems in the most prominent topographic lows of the Interior Plateau. We conclude that the CIS underwent a large-scale reconfiguration early during deglaciation and was subsequently diminished by thinning and complex frontal retreat towards the Coast Mountains.
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| 3. |
- Margold, Martin, et al.
(författare)
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Timing of terminal Pleistocene deglaciation at high elevations in southern and central British Columbia constrained by Be-10 exposure dating
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 99, s. 193-202
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Tidskriftsartikel (refereegranskat)abstract
- The Cordilleran Ice Sheet (CIS) covered most of British Columbia and southern Yukon Territory at the local Last Glacial Maximum (ILGM) during Marine Oxygen Isotope Stage 2. However, its subsequent demise is not well understood, particularly at high elevations east of its ocean-terminating margin. We present Be-10 exposure ages from two high-elevation sites in southern and central British Columbia that help constrain the time of initial deglaciation at these sites. We sampled granodiorite erratics at elevations of 2126-2230 m a.s.l. in the Marble Range and 1608-1785 m a.s.l. in the Telkwa Range at the western margin of the Interior Plateau. The erratics at both sites are near ice-marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation. The locations of the erratics and their relations to meltwater channels ensure that the resulting Be-10 ages date CIS deglaciation and not the retreat of local montane glaciers. Our sample sites emerged above the surface of the CIS as its divide migrated westward from the Interior Plateau to the axis of the Coast Mountains. Two of the four samples from the summit area of the Marble Range yielded apparent exposure ages of 14.0 +/- 0.7 and 15.2 +/- 0.8 ka. These ages are 1.8-3.0 ka younger than the well-established ILGM age of ca 17 ka for the Puget lobe of the CIS in Washington State; they are 1.7 ka younger than the ILGM age for the Puget lobe if a snow-shielding correction to their uncertainty-weighted mean age is applied. The other two samples yielded much older apparent exposure ages (20.6 +/- 1.4 and 33.0 +/- 1.5 ka), indicating the presence of inherited isotopes. Four samples collected from the summit area of the Telkwa Range in the Hazelton Mountains yielded well clustered apparent exposure ages of 10.1 +/- 0.6, 10.2 +/- 0.7, 10.4 +/- 0.5, and 11.5 +/- 1.1 ka. Significant present-day snow cover introduces a large uncertainty in the apparent exposure ages from this site. A snow-shielding correction based on present-day snow cover data increases the uncertainty-weighted mean exposure age of the Telkwa Range erratics to 12.4 +/- 0.7 ka, consistent with deglacial C-14 ages from areas near sea level to the west. Our exposure ages show a thinning of the southern portion of the CIS shortly after the ILGM and persistence of a remnant mountain ice cap in the central Coast Mountains into the Younger Dryas Chronozone. Our data also show that the summit area of the Marble Range was ice-covered during the ILGM. The presence of an ice body of considerable dimension in north-central British Columbia until, or possibly even after, the Younger Dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the Skeena Mountains in northwest British Columbia and the need for better understanding of the response of the CIS to Lateglacial climate fluctuations.
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| 4. |
- Stroeven, Arjen, 1963-, et al.
(författare)
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Investigating the glacial history of the northern sector of the Cordilleran Ice Sheet with cosmogenic 10Be concentrations in quartz
- 2010
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3630-3643
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Tidskriftsartikel (refereegranskat)abstract
- Exposure durations of glacial landforms in widely separated areas of central Yukon Territory affected bythe northern sector of the Cordilleran Ice Sheet (CIS) and alpine glaciers have been determined usingcosmogenic 10Be in quartz. The aim of our research is to test previous reconstructions of glacial historyand to begin to address the paucity of chronological control for the lateral and vertical extent of thenorthern CIS. Chronological evidence for CIS expansion predating the Last Glacial Maximum comes fromminimum surface exposure durations of c 100 ka for two bedrock samples within the Reid glacial limit,indicating a possible marine Oxygen Isotope Stage (OIS) 6 age for this event, and from minimumexposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatakwithin the McConnell glacial limit (OIS 2), indicating a possible OIS 4 age. High elevation minimumsurface exposure durations within the McConnell limit indicate that some areas formerly mapped asnunataks were covered by cold-based ice prior to 30 ka. Montane glaciation in the Mackenzie Mountains,outside the McConnell glacial limit, was contemporaneous with nearby CIS advance at 17 ka, with CISretreat by 15 ka. Deglaciation of the Tintina Trench, a major ice discharge route, was completed by 12 ka.At this time ice in an adjacent discharge route to the south was still entering higher-elevation valleys inthe Pelly Mountains. A Lateglacial readvance may have peaked at ca 10 ka in the Ogilvie Mountains.Considerable variation in ages from individual landforms, and possible complex histories, requireadditional cosmogenic nuclide measurements to confirm interpretations.
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| 5. |
- Stroeven, Arjen P., et al.
(författare)
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Investigating absolute chronologies of glacial advances in the NW sector of the Cordilleran Ice Sheet with terrestrial in situ cosmogenic nuclides
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 92, s. 429-443
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Tidskriftsartikel (refereegranskat)abstract
- Geologic mapping in Yukon Territory, Canada, over the past 100 years has revealed a consistent pattern of diminishing Cordilleran Ice Sheet (CIS) extent during successively younger glaciations. Although this pattern is generally accepted, there is still much uncertainty about the number of glaciations, their ages, and the dynamics of the different lobes that constituted the digitate ice sheet margin, their subglacial thermal regimes, and ice thicknesses. We address uncertainties in the timing of glaciation using cosmogenic nuclide exposure dating at key localities that straddle several major lobes of the CIS in west-central Yukon Territory. Differences in exposure duration within what are thought to be the same map units are perhaps due to inheritance (older than expected), but more likely result from postglacial shielding (younger than expected) or surface erosion. Despite a significant spread in exposure durations on moraines and within map units, and tending to rely on longest exposure durations on moraines due to postglacial degradation and shielding, our results indicate that the McConnell glacial advance occurred during Marine Oxygen Isotope Stage (MIS) 2, judging from oldest minimum apparent exposure ages of 15.7 +/- 1.5 and 17.7 +/- 1.6 ka, a Gladstone glacial advance occurred before 51.8 +/- 4.7 ka (MIS 4) and Reid glacial advances before 79.8 +/- 7.3 and 82.8 +/- 7.5 ka (consistent with MIS 6). Traces of even older glacial advances predate 100 ka (107.5 +/- 9.9-154.3 +/- 14.2 ka).
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