Linking gene expression in the intestine to production of gametes through the phosphate transporter PITR-1 in Caenorhabditis elegans

Inorganic phosphate is an essential mineral for both prokaryotic and eukaryotic cell metabolism and structure. Its uptake into the cell is mediated by membrane bound transporters and coupled to Na+ transport. Mammalian sodium-dependent Pi co-transporters have been grouped into three families NaPi-I, NaPi-II, and NaPi-III. Despite being discovered more than 2 decades ago, very little is known about requirements for NaPi-III transporters in vivo, in the context of intact animal models. Here we find that impaired function of the C. elegans NaPi-III transporter, pitr-1, results in decreased brood size and dramatically increased expression of vitellogenin by the worm intestine. Unexpectedly, we found that the effects of pitr-1 mutation on vitellogenin expression in the intestine could only be rescued by expression of pitr-1 in the germline, and not by expression of pitr-1 in the intestine itself. Our results indicate the existence of a signal from the germline that regulates gene expression in the intestine, perhaps linking nutrient export from the intestine to production of gametes by the germline

Glacier maxima in Baffin Bay during the Medieval Warm Period coeval with Norse settlement

The climatic mechanisms driving the shift from the Medieval Warm Period (MWP) to the Little Ice Age (LIA) in the North Atlantic region are debated. We use cosmogenic beryllium-10 dating to develop a moraine chronology with century-scale resolution over the last millennium and show that alpine glaciers in Baffin Island and western Greenland were at or near their maximum LIA configurations during the proposed general timing of the MWP. Complimentary paleoclimate proxy data suggest that the western North Atlantic region remained cool, whereas the eastern North Atlantic region was comparatively warmer during the MWP—a dipole pattern compatible with a persistent positive phase of the North Atlantic Oscillation. These results demonstrate that over the last millennium, glaciers approached their eventual LIA maxima before what is considered the classic LIA in the Northern Hemisphere. Furthermore, a relatively cool western North Atlantic region during the MWP has implications for understanding Norse migration patterns during the MWP. Our results, paired with other regional climate records, point to nonclimatic factors as contributing to the Norse exodus from the western North Atlantic region

Effect of selection on ancestry: an exactly soluble case and its phenomenological generalization

We consider a family of models describing the evolution under selection of a population whose dynamics can be related to the propagation of noisy traveling waves. For one particular model, that we shall call the exponential model, the properties of the traveling wave front can be calculated exactly, as well as the statistics of the genealogy of the population. One striking result is that, for this particular model, the genealogical trees have the same statistics as the trees of replicas in the Parisi mean-field theory of spin glasses. We also find that in the exponential model, the coalescence times along these trees grow like the logarithm of the population size. A phenomenological picture of the propagation of wave fronts that we introduced in a previous work, as well as our numerical data, suggest that these statistics remain valid for a larger class of models, while the coalescence times grow like the cube of the logarithm of the population size.Comment: 26 page

Survival of near-critical branching Brownian motion

Consider a system of particles performing branching Brownian motion with negative drift $\mu = \sqrt{2 - \epsilon}$ and killed upon hitting zero. Initially there is one particle at $x>0$. Kesten showed that the process survives with positive probability if and only if $\epsilon>0$. Here we are interested in the asymptotics as \eps\to 0 of the survival probability $Q_\mu(x)$. It is proved that if $L= \pi/\sqrt{\epsilon}$ then for all $x \in \R$, $\lim_{\epsilon \to 0} Q_\mu(L+x) = \theta(x) \in (0,1)$ exists and is a travelling wave solution of the Fisher-KPP equation. Furthermore, we obtain sharp asymptotics of the survival probability when $x<L$ and $L-x \to \infty$. The proofs rely on probabilistic methods developed by the authors in a previous work. This completes earlier work by Harris, Harris and Kyprianou and confirms predictions made by Derrida and Simon, which were obtained using nonrigorous PDE methods

The Egg Surface LDL Receptor Repeat-Containing Proteins EGG-1 and EGG-2 Are Required for Fertilization in Caenorhabditis elegans

SummaryThe molecular machinery that mediates sperm-egg interactions at fertilization is largely unknown. We identify two partially redundant egg surface LDL receptor repeat-containing proteins (EGG-1 and EGG-2) that are required for Caenorhabditis elegans fertility in hermaphrodites, but not males. Wild-type sperm cannot enter the morphologically normal oocytes produced by hermaphrodites that lack egg-1 and egg-2 function despite direct gamete contact. Furthermore, we find that levels of meiotic maturation/ovulation and sperm migratory behavior are altered in egg-1 mutants. These observations suggest an unexpected regulatory link between fertilization and other events necessary for reproductive success. egg-1 and egg-2 are the result of a gene duplication in the nematode lineage leading to C. elegans. The two closely related species C. briggsae and C. remanei encode only a single egg-1/egg-2 homolog that is required for hermaphrodite/female fertility. In addition to being the first identified egg components of the nematode fertilization machinery, the egg-1 and egg-2 gene duplication could be vital with regards to maximizing C. elegans fecundity and understanding the evolutionary differentiation of molecular function and speciation

Pinedale Glacial History of the Upper Arkansas River Valley: New Moraine Chronologies, Modeling Results and Geologic Mapping

This field trip guidebook chapter outlines the glacial history of the upper Arkansas River valley, Colorado, and builds on a previous GSA field trip to the same area in 2010. The following will be presented: (1) new cosmogenic 10Be exposure ages of moraine boulders from the Pinedale and Bull Lake glaciations (Marine Isotope Stages 2 and 6, respectively) located adjacent to the Twin Lakes Reservoir, (2) numerical modeling of glaciers during the Pinedale glaciation in major tributaries draining into the upper Arkansas River, (3) discharge estimates for glacial-lake outburst floods in the upper Arkansas River valley, and (4) 10Be ages on flood boulders deposited downvalley from the moraine sequences. This research was stimulated by a new geologic map of the Granite 7.5’ quadrangle, in which the mapping of surficial deposits was revised based in part on the interpretation of newly acquired LiDAR data and field investigations. The new 10Be ages of the Pinedale terminal moraine at Twin Lakes average 21.8 ± 0.7 ka (n=14), which adds to nearby Pinedale terminal moraine ages of 23.6 ± 1.4 ka (n=5), 20.5 ± 0.2 ka (n=3) and 16.6 ± 1.0 ka, and downvalley outburst flood terraces that date to 20.9 ± 0.9 ka (n=4) and 19.0 ± 0.6 ka (n=4). This growing chronology leads to improved understanding of the controls and timing of glaciation in the western U.S., the modeling of glacial-lake outburst flooding, and the reconstruction of paleo-temperature through glacier modeling

Cutting edges at random in large recursive trees

We comment on old and new results related to the destruction of a random recursive tree (RRT), in which its edges are cut one after the other in a uniform random order. In particular, we study the number of steps needed to isolate or disconnect certain distinguished vertices when the size of the tree tends to infinity. New probabilistic explanations are given in terms of the so-called cut-tree and the tree of component sizes, which both encode different aspects of the destruction process. Finally, we establish the connection to Bernoulli bond percolation on large RRT's and present recent results on the cluster sizes in the supercritical regime.Comment: 29 pages, 3 figure

Exploring student engagement in sustainability education and study abroad

This paper specifically outlines an investigation of the influence of sustainability education and study abroad coursework on levels of a key component of academic success, student engagement. A quasi-experimental design compared pretest and posttest levels of engagement (measured by the Deep Learning Scale) among undergraduate students enrolled in four types of courses). Data were analyzed using a repeated measures MANOVA and supported two significant 2-way interactions (Sustainability * Time and Study Abroad * Time) suggesting that student engagement (Deep Learning) is more likely to increase with sustainability (than non-sustainability) courses and with study abroad (than non-study abroad/campus courses). Findings provide empirical support for university initiatives that seek to incorporate sustainability coursework and study abroad opportunities into the undergraduate curriculum as means to enhance students’ overall engagement and academic success. The paper provides insights into where sustainability education and study abroad courses have broad potential to promote engagement and, as such, should be considered part of the general learning requirement of university education. In terms of study limitations, the sample is drawn from one university and self-selection bias is possible for students choosing to enroll in study abroad and sustainability-focused courses