Archive for December, 2007
Towards predicting streamflow based on SWE, melt timing, and topography in subarctic heterogeneous terrain
Snowmelt onset date and snow water equivalent (SWE) are major factors that influence the spring runoff in high latitude, snow dominated basins. We combine AMSR-E L3 daily SWE from March to June 2003-2006, daily hydrological records from 3 sites on the Pelly and Ross Rivers, Yukon Territory [Pelly Crossing N62.82, W136.58, Faro N62.22,W133.37, and Ross River N61.99,W132.37], and a 1:250,000 DEM to develop a technique to predict streamflow in subarctic heterogeneous terrain. The AMSR-E L3 SWE algorithm was developed for global snow cover distributions; it is not optimized for heterogeneous terrain. Field data suggest that it underestimates the SWE in this area. We assume it represents the minimum SWE per pixel. SWE variations of the Pelly River basin (49,000 km2) and its two nested sub-basins (22,100 km2 and 7,250 km2), show that SWE had an apparent drop shortly after the snowmelt onset date determined from Tb and diurnal amplitude variations (DAV), which are also correlated with temperature change. During the early stage of snowmelt, high and low elevations have no significant SWE difference. After mid-April, the most intense melt period at lower elevations, low elevation SWE drops far below high elevation SWE, which is just beginning the melt process. Initial melt and the drop in low elevation SWE likely cause the first small discharge peak in the hydrograph. When the SWE throughout the basin approaches 0 mm for more than 3 days, it is followed by the peak flow. The largest basin has an ~14 day lag between the SWE drop and the flow increase, while the smaller basins have an about 9 day lag. Snow distribution, melt, runoff, and the lag times vary due to diverse terrain and microclimate factors such as: forest cover, permafrost, temperature and precipitation. By combining topography, snow distribution and melt timing, we have developed an understanding of basin-specific stream discharge response to spring thaw. Passive microwave derived daily SWE data combined with terrain and melt timing have significant potential for constraining and predicting stream flow timing and magnitude during the melt season in subarctic regions.
Direct measurement of hematite individual particle anisotropy: implications for inclination shallowing in red bed DRMs.
Methods to correct for the observed inclination shallowing in sedimentary rocks have been proposed that are based on either models of the geomagnetic field and the resulting directional distribution of paleomagnetic vectors or the magnetic anisotropy of the magnetic minerals carrying the remanence. One limitation of the anisotropy method for hematite-bearing red beds has been the isolation and determination of a rocks detrital hematite individual particle anisotropy. Up to now, our red bed inclination shallowing corrections have been dependent on estimates of hematite individual particle anisotropy using data fit to theoretical correction curves. › Continue reading
The Role of Cohesion Establishment in Genomic Maintenance
Genome fidelity and cell fitness relies on a system that ensures that each daughter cell obtain a single copy and only a single copy of every chromosome while maintaining genomic integrity through repair processes. Previously, cohesion establishment was shown to act during S phase through Ctf7p/Eco1p (Skibbens et al 1999, Toth et al 1999) and more recently during DNA damage repair (Sjogren and Nasmyth 2001, Strom et al2007, Unal et al 2007). Although little is known about the process of cohesion establishment research has linked Ctf7p to replication factors PCNA (Skibbens et al 1999, Moldovan et al 2006) and RFC large subunits Rfc1p, Ctf18p and Rad24p (Skibbens et al 1999, Kenna and Skibbens 2003). This information lead us to hypothesize that Elg1p, the least characterized of large RFC alternative subunits, may also be implicated in cohesion establishment. Genetic screens revealed a role for Elg1p in homologous recombination, replication fork restart, S phase checkpoint pathways and Okazaki fragment maturation (Bellaoui et al 2003, Ben-Aroya et al 2003, Kanellis et al 2003, Banerjee and Myung 2004, Ayora and Kupiec 2005).
Here we show a novel physical and genetic interaction between cohesion establishment factor Ctf7p and alternative RFC large subunit Elg1p. Pull down experiments involving Ctf7p-Gst (Bait) and Elg1p-Myc13 (target) showed a novel physical interaction between these two proteins. Furthermore, ctf7-203 temperature sensitivity is partially suppressed by deletion of ELG1. These results suggest a role for cohesion establishment factor Ctf7p in genome integrity and maintenance.
Loss of Endogenous Oncoprotein18/Stathmin in Mouse Embryo Fibroblasts Induces Changes in Tubulin Isoform Expression with Minimal Changes to Microtubule Dynamics
Op18/Stathmin is a ubiquitous microtubule (MT) destabilizing protein linked to cancer and cell health: Op18 is over-expressed in leukemias and its expression level correlates with breast cancer stage progression. We are using MEFs (mouse embryonic fibroblasts) WT (+/+), heterozygous (+/-), or knockout (-/-) for the Op18 gene to further characterize Op18s roles in MT polymerization and dynamics. MT polymer level and nucleation rate increased with loss of Op18. In contrast, loss of one or both copies of the Op18 gene results in surprisingly modest changes to MT dynamics. For example MT dynamicity, a measure of total tubulin addition and loss from MT ends, and catastrophe frequency were similar in all three lines. Since MT dynamics depend on tubulin (Tb) isotype composition (Panda et al., 1994), we used quantitative reverse transcription-PCR to measure differences in mRNA levels for each Tb isotype. The alpha-Tb I mRNA level did not change across genotypes, but protein level nearly doubled in the (-/-) line compared to WT. Cells (-/-) for Op18 also under-express mRNA for Tbs II (20% less) and IV (36% less) and over-express Tb III (78% more) compared to WT. This change in Tb isotype expression is consistent with that observed in taxol-resistant breast cancer cells (Shalli et al., 2005). Other differentially regulated mRNAs include increases in alpha-Tb VII and VIII, and Tb VII. We conclude that cells respond to loss of Op18 by changing the ratio of tubulin isoforms, allowing cells to maintain dynamic MT turnover. We hypothesize that it is changes to MT polymer content and specific Tb isoform expression, rather than changes to MT dynamics, that are responsible for Op18s role in cancer and cell survival. Thanks to Jutta Marzillier, Lehigh Genomics Facility, and G. Shyumyatsky, Rutgers University (mice).
Funded by NIH.
Inhibition of Gap Junction Intercellular Communication in Response to Activation of G-protein Coupled Receptors is Mediated via Gap Junction Internalization
Communication between adjacent cells through gap junctions (GJs) occurs in nearly every tissue and is fundamental to coordinated cell behavior during development, differentiation, and tissue homeostasis. While both the regulation and complete inhibition of gap junction intercellular communication (GJIC) have been well documented, surprisingly little is known about how this modulation is actually achieved. GJ channels can open and close (gate) in response to physiological parameters, including intracellular pH, Ca2+ concentration, and connexin phosphorylation. However, GJIC could also be rapidly down-regulated through internalization of whole or portions of GJ plaques, as shown recently by our lab (Piehl et al., 2007, MBC 18, 337). Van Zeijl et al., (2007, JCB 177, 881) subsequently reported a rapid inhibition of Cx43-based GJIC in response to activation of the Gαq/PLCβ3-PIP2 hydrolysis pathway; however, they did not investigate how this inhibition is achieved. Here we report that activation of the Gαq/PLCβ3-PIP2 hydrolysis pathway by the inflammatory mediators, thrombin and endothelin (native Gαq agonists), or the wasp toxin mastoparan (a constitutive activator of Gαq) correlates with GJ internalization and concomitant inhibition of GJIC. Immunofluorescence imaging revealed that, in primary vascular endothelial cells (PAECs), in response to stimulation with these G-protein coupled receptor (GPCR) agonists, connexin-43 (Cx43) is rapidly internalized into intracellular GJ vesicles. Statistical analysis shows a significant decrease of GJs at the PM and a significant increase of intracellular vesicular Cx43 as compared to untreated controls. Activation of this signaling pathway results in a complete inhibition of GJIC measured by lucifer yellow scrape loading dye transfer. In controls treated with suramin (a Gαq antagonist) in the presence of thrombin, endothelin and mastoparan, GJIC is restored to wt levels as measured by Lucifer yellow scrape loading dye transfer. Ultrastructural analysis demonstrates the presence of numerous intracellular double-membrane vesicles exhibiting typical morphology of internalized GJs. These results indicate that inhibition of GJIC in response to activation of GPCRs is mediated via the internalization of GJs and suggest that inhibition of GJIC is a physiological function of GJ internalization.