Vincent Cheng

Support for the immortal strand hypothesis neural stem cells partition DNA asymmetrically in vitro

The immortal strand hypothesis proposes that asymmetrically dividing stem cells (SCs) selectively segregate chromosomes that bear the oldest DNA templates. We investigated cosegregation in neural stem cells (NSCs). After exposure to the thymidine analogue 5-bromo-2-deoxyuridine (BrdU), which labels newly synthesized DNA, a subset of neural precursor cells were shown to retain BrdU signal. It was confirmed that some BrdU-retaining cells divided actively, and that these cells exhibited some characteristics of SCs. This asymmetric partitioning of DNA then was demonstrated during mitosis, and these results were further supported by real time imaging of SC clones, in which older and newly synthesized DNA templates were distributed asymmetrically after DNA synthesis. We demonstrate that NSCs are unique among precursor cells in the uneven partitioning of genetic material during cell divisions.

Probability of Tornado Occurrence across Canada

The number of tornado observations in Canada is believed to be significantly lower than the actual occurrences. To account for this bias, the authors propose a Bayesian modeling approach founded upon the explicit consideration of the population sampling bias in tornado observations and the predictive relationship between cloud-to-ground (CG) lightning flash climatology and tornado occurrence. The latter variable was used as an indicator for quantifying convective storm activity, which is generally a precursor to tornado occurrence. The CG lightning data were generated from an 11-yr lightning climatology survey (1999‐2009) from the Canadian Lightning Detection Network. The results suggest that the predictions of tornado occurrence in populated areas are fairly reliable with no profound underestimation bias. In sparsely populated areas, the analysis shows that the probability of tornado occurrence is significantly higher than what is represented in the 30-yr data record. Areas with low population density but high lightning flash density demonstrate the greatest discrepancy between predicted and observed tornado occurrence. A sensitivity analysis with variousgridsizes was alsoconducted. It wasfound that thepredictivestatementssupportedby themodel are fairlyrobusttothegrid configuration,but thepopulationdensity pergrid cellis more representativetothe actual population density at smaller resolution and therefore more accurately depicts the probability of tornado occurrence. Finally, a tornado probability map is calculated for Canada based on the frequency of tornado occurrence derived from the model and the estimated damage area of individual tornado events.

Neurogenic potential of isolated precursor cells from early post-gastrula somitic tissue.

Adult tissues are known to contain rare populations of stem cells with multilineage differentiation potential that are distinct from other resident tissue-specific stem cells. However, whether multilineage stem cells are involved in tissue development is uncertain, primarily because the identification and characterization of these cells in embryonic tissue primordia is not well established. We tested whether stem cells with multilineage potential are present within the early post-gastrula somite tissue. We show that clonally derived precursor cells generate colonies with self-renewal capacity and have both neurogenic and myogenic lineage potential. Somite colonies contain cells that express Sox2, nestin, and Sca1, but do not express genes indicative of somitic mesoderm specification. Furthermore, we demonstrate that this multilineage potential is not due to colony cells with a pluripotent epiblast identity or the selection of p75 receptor-positive neural crest stem cells. Despite utilizing a highly undifferentiated tissue source, colony formation was not enhanced relative to reported estimates of multilineage stem cells from adult muscle, a derivative of the embryonic somite. Thus, our findings suggest that a permissive in vitro environment is sufficient for the isolation of a discrete population of stem cells in the embryonic somite that may represent the earliest developmental precursor to adult muscle multilineage stem cells.

A Bayesian modelling framework for tornado occurrences in North America

Tornadoes represent one of natures most hazardous phenomena that have been responsible for significant destruction and devastating fatalities. Here we present a Bayesian modelling approach for elucidating the spatiotemporal patterns of tornado activity in North America. Our analysis shows a significant increase in the Canadian Prairies and the Northern Great Plains during the summer, indicating a clear transition of tornado activity from the United States to Canada. The linkage between monthly-averaged atmospheric variables and likelihood of tornado events is characterized by distinct seasonality; the convective available potential energy is the predominant factor in the summer; vertical wind shear appears to have a strong signature primarily in the winter and secondarily in the summer; and storm relative environmental helicity is most influential in the spring. The present probabilistic mapping can be used to draw inference on the likelihood of tornado occurrence in any location in North America within a selected time period of the year.

Implications of projected climate change on winter road systems in Ontario’s Far North, Canada

Understanding climate change impacts on winter road systems in Ontario’s Far North is critical due to the high dependence on such seasonal corridors by local residences, particularly among remote First Nations communities. In recent years, a warmer climate has resulted in a shorter winter road season and an increase in unreliable road conditions, thus limiting access among remote communities. This study focused on examining the future freezing degree day (FDD) accumulations during the preconditioning period of the winter roads at five locations using the multi-model ensembles of general circulation models (GCMs) and regional climate models (RCMs), under the representative concentration pathway (RCP) scenarios. The Statistical DownScaling Model Decision Centric Version 5 (SDSM-DC) was applied to validate the baseline climate. The results from the CMIP5 showed that by mid-century, the trends of FDDs under RCP4.5 for Moosonee and Kapuskasing were projected to decrease below the lowest threshold with the mean FDDs at 376 and 363, respectively. Under RCP8.5, the mean FDDs for Lansdowne House and Red Lake were projected to be below the lowest threshold, at 356 and 305, respectively, by the end of the century. Results of the FDD threshold measure indicated that climate conditions would possibly be unfavorable during the winter road construction period by mid-century for Moosonee and Kapuskasing and for Lansdowne House and Red Lake by the end of the century. For Big Trout Lake, on the other hand, climate conditions are expected to remain favorable for the winter road construction through the end of 2100.

Detection of spatial and temporal hydro-meteorological trends in Lake Michigan, Lake Huron and Georgian Bay

The Laurentian Great Lakes represent the largest freshwater basin on Earth, containing 21% of the worlds surface fresh water by volume. Water level fluctuations are an on-going concern and have received considerable attention in the area. We present a trend analysis of meteorological (air temperature, cloud cover, and wind speed) and hydrological (precipitation, runoff, and evaporation) variables for Lake Michigan, Lake Huron, and Georgian Bay. Using the non-parametric Mann-Kendall test, our analysis identified significant upward trends in daily minimum air temperature, whereas daily maximum air temperature demonstrated weakly decreasing trends in space and time. Evaporation was found to be increasing from late spring until early fall and this pattern may be explained by the shortening of the ice/snow cover period, which results in faster warming of lake surface due to the induced variations in albedo feedback. Time-series analysis of the over-lake precipitation revealed mostly non-significant statistical trends. Recent temperature increases may have led to elevated winter runoff in the Great Lakes region, given that precipitation falls mainly as rain instead of snow. We also provide clear evidence of reduced cloud cover and wind speed. Our study offers critical insights into the patterns of within- and among-year variability of hydro-meteorological variables useful in elucidating the mechanisms that modulate water levels in the Great Lakes.

Near-Time Sea Surface Temperature and Tropical Cyclone Intensity in the Eastern North Pacific Basin

Although a significant relationship between near-time sea surface temperature (SST) and tropical cyclone (TC) intensity has been found for many major TC basins, this topic has not been explored in the eastern North Pacific (ENP) basin. When the main development region of the (ENP) Ocean is subdivided into eastern (EDR) and western (WDR) development regions, SSTs show a weak, yet significant, positive relationship with intensities of the six-hourly TC observations and storms’ maximum strengths only in the WDR. This SST-storm intensity relationship is most apparent for the maximum lifetime TC intensity of WDR major hurricanes. The maximum strength of major hurricanes in the ENP basin is more clearly established in the WDR where SST is at least 25 °C, well below the minimum SST value that is observed in the North Atlantic basin.

Predicting the Climatology of Tornado Occurrences in North America with a Bayesian Hierarchical Modeling Framework

Destruction and fatalities from recent tornado outbreaks in North America have raised considerable concerns regarding their climatic and geographic variability. However, regional characterization of tornado activity in relation to large-scale climatic processes remains highly uncertain. Here, a novel Bayesian hierarchical framework is developed for elucidating the spatiotemporal variability of the factors underlying tornado occurrence in North America. It is demonstrated that regional variability of tornado activity can be characterized using a hierarchical parameterization of convective available potential energy, storm relative helicity,andverticalwindshearquantities.It isshownthatthespatialvariabilityoftornadooccurrenceduring thewarmsummerseasoncanbeexplainedbyconvectiveavailablepotentialenergyandstormrelativehelicity alone, while vertical wind shear is clearly better at capturing the spatial variability of the cool season tornado activity. The results suggest that the Bayesian hierarchical modeling approach is effective for understanding the regional tornadic environment and in forming the basis for establishing tornado prognostic tools in North America.

Erratum: A Bayesian modelling framework for tornado occurrences in North America

Nature Communications 6: Article number:6599 (2015); Published 25 March 2015; Updated 5 June 2015. The captions of Figs 2 and 3 of this Article contain typographical errors that were introduced during the production process. In both Figs 2 and 3, the units for the tornado occurrences should be 10,000 km2·yr−1 rather than 100 km2·yr−1.