Spatial and temporal variations in precipitation and cloud interception in the Sierra Nevada of central California

Spatial and temporal variations in patterns of precipitation and cloud interception were studied for a period of 14 months in the Sierra Nevada of central California. 14 fully automated sampling stations, located at elevations from 800 to 2400 m, were utilized in the study. Both precipitation and cloud interception were observed to increase with elevation. Cloudwater deposition increased at higher elevations due both to a greater frequency of cloud interception and higher wind speeds. Cloudwater deposition, caused primarily by the interception of clouds associated with cold fronts approaching from the north or north-west, is most important at elevations above 1500 m; however, the interception of highly polluted winter “Tule” fogs, lifting above the floor of the San Joaquin Valley, appears to be an important mechanism for cloudwater deposition at lower elevation sites. Observed and estimated hydrological and chemical inputs to the passive cloudwater collectors used in the study were substantial, suggesting that cloud interception may contribute significantly to the same inputs for exposed conifers in the region

Prolonging somatic cell proliferation through constitutive hox gene expression in C. elegans

hox genes encode a conserved family of homeodomain transcription factors that are essential to determine the identity of body segments during embryogenesis and maintain adult somatic stem cells competent to regenerate organs. In contrast to higher organisms, somatic cells in C. elegans irreversibly exit the cell cycle after completing their cell lineage and the adult soma cannot regenerate. Here, we show that hox gene expression levels in C. elegans determine the temporal competence of somatic cells to proliferate. Down-regulation of the central hox gene lin-39 in dividing vulval cells results in their premature cell cycle exit, whereas constitutive lin-39 expression causes precocious Pn.p cell and sex myoblast divisions and prolongs the proliferative phase of the vulval cells past their normal point of arrest. Furthermore, ectopic expression of hox genes in the quiescent anchor cell re-activates the cell cycle and induces proliferation until young adulthood. Thus, constitutive expression of a single hox transcription factor is sufficient to prolong somatic cell proliferation beyond the restriction imposed by the cell lineage. The down-regulation of hox gene expression in most somatic cells at the end of larval development may be one cause for the absence of cell proliferation in adult C. elegans

Cloud water chemistry in Sequoia National Park

Interception of cloudwater by forests in the Sierra Nevada Mountains may contribute significantly to acidic deposition in the region. Cloudwater sampled in Sequoia National Park had pH values ranging from 4.4 to 5.7. The advance of cold fronts into the Park appears to lead to higher aerosol and gas phase concentrations than are seen under normal mountain-valley circulations, producing higher cloud-water concentrations than might otherwise be expected. Estimates of annual deposition rates of NO_3^−, SO_4^(2−), NH_4^+ and H^+ due to cloudwater impaction are comparable to those measured in precipitation

The Caenorhabditis elegans homolog of the Evi1 proto-oncogene, egl-43, coordinates G1 cell cycle arrest with pro-invasive gene expression during anchor cell invasion.

Cell invasion allows cells to migrate across compartment boundaries formed by basement membranes. Aberrant cell invasion is a first step during the formation of metastases by malignant cancer cells. Anchor cell (AC) invasion in C. elegans is an excellent in vivo model to study the regulation of cell invasion during development. Here, we have examined the function of egl-43, the homolog of the human Evi1 proto-oncogene (also called MECOM), in the invading AC. egl-43 plays a dual role in this process, firstly by imposing a G1 cell cycle arrest to prevent AC proliferation, and secondly, by activating pro-invasive gene expression. We have identified the AP-1 transcription factor fos-1 and the Notch homolog lin-12 as critical egl-43 targets. A positive feedback loop between fos-1 and egl-43 induces pro-invasive gene expression in the AC, while repression of lin-12 Notch expression by egl-43 ensures the G1 cell cycle arrest necessary for invasion. Reducing lin-12 levels in egl-43 depleted animals restored the G1 arrest, while hyperactivation of lin-12 signaling in the differentiated AC was sufficient to induce proliferation. Taken together, our data have identified egl-43 Evi1 as an important factor coordinating cell invasion with cell cycle arrest

A DNA replication-independent function of pre-replication complex genes during cell invasion in C. elegans

Cell invasion is an initiating event during tumor cell metastasis and an essential process during development. A screen of C. elegans orthologs of genes overexpressed in invasive human melanoma cells has identified several components of the conserved DNA pre-replication complex (pre-RC) as positive regulators of anchor cell (AC) invasion. The pre-RC genes function cell-autonomously in the G1-arrested AC to promote invasion, independently of their role in licensing DNA replication origins in proliferating cells. While the helicase activity of the pre-RC is necessary for AC invasion, the downstream acting DNA replication initiation factors are not required. The pre-RC promotes the invasive fate by regulating the expression of extracellular matrix genes and components of the PI3K signaling pathway. Increasing PI3K pathway activity partially suppressed the AC invasion defects caused by pre-RC depletion, suggesting that the PI3K pathway is one critical pre-RC target. We propose that the pre-RC, or a part of it, acts in the postmitotic AC as a transcriptional regulator that facilitates the switch to an invasive phenotype

Active cloudwater collector

A cloud water collector is disclosed comprised of a sampler duct having a plurality of spaced Teflon strands, in the form of screens, mounted across the conduit at an acute angle facing the open inlet of the conduit. Droplets in a cloud sample are drawn into the conduit by a fan located at the back end of the conduit, impact upon the Teflon strands and are drawn down to the lower ends of the strands, where they drop and the accumulated droplets are diverted to a sample bottle for collection. The cloud water collector can be automated to collect a plurality of successive cloud water samples by an automated sampler containing a reservoir into which cloud water obtained in the cloud water collector is discharged. A motor-driven turntable is provided which holds a plurality of sample bottles. When the reservoir is filled to a predetermined volume, apparatus, such as a liquid level sensor, actuates a valve to open same and discharge the liquid sample from the reservoir into one of the bottles at a filling station on the turntable. The valve then closes and the turntable rotates to index the next bottle beneath the reservoir at the filling station, and the operation is repeated to fill the latter bottle. When all of the bottles on the turntable have been filled, the indexing mechanism is deactivated and liquid accumulating in the reservoir is diverted to an overflow bottle

Vertical Transport Rates in the Stratosphere in 1993 from Observations of CO2, N2O and CH4

Measurements of CO2, N2O and CH4 are analyzed to define hemispheric average vertical exchange rates in the lower stratosphere from November 1992 to October 1993. Effective vertical diffusion coefficients were small in summer, less than or equal to 1 m(exp 2)/sec at altitudes below 25 km; values were similar near the tropopause in winter, but increased markedly with altitude. The analysis suggests possibly longer residence times for exhaust from stratospheric aircraft, and more efficient transport from 20 km to the middle stratosphere, than predicted by many current models. Seasonally-resolved measurements of stratospheric CO2 and N2O provide significant new constraints on rates for global-scale vertical transport