Of towers, walls, and fields: perspectives on language in science

Language in science is in the midst of change and appears dominated by two contradictory trends. Globalization of scientific English seems to promise greater international unity, while growth of field-specific jargon suggests communicational diaspora. Real in part, each trend is complex and multileveled, and includes elements of convergence and divergence, along with important implications for the present and future of technical knowledge.     

Microbial activity at gigapascal pressures

We observed physiological and metabolic activity of Shewanella oneidensis strain MR1 and Escherichia coli strain MG1655 at pressures of 68 to 1680 megapascals (MPa) in diamond anvil cells. We measured biological formate oxidation at high pressures (68 to 1060 MPa). At pressures of 1200 to 1600 MPa, living bacteria resided in fluid inclusions in ice-VI crystals and continued to be viable upon subsequent release to ambient pressures (0.1 MPa). Evidence of microbial viability and activity at these extreme pressures expands by an order of magnitude the range of conditions representing the habitable zone in the solar system.     

Early Permian bipedal reptile

A 290-million-year-old reptilian skeleton from the Lower Permian (Asselian) of Germany provides evidence of abilities for cursorial bipedal locomotion, employing a parasagittal digitigrade posture. The skeleton is of a small bolosaurid, Eudibamus cursoris, gen. et sp. nov. and confirms the widespread distribution of Bolosauridae across Laurasia during this early stage of amniote evolution. E. cursoris is the oldest known representative of Parareptilia, a major clade of reptiles.     

PirB is a functional receptor for myelin inhibitors of axonal regeneration

A major barrier to regenerating axons after injury in the mammalian central nervous system is an unfavorable milieu. Three proteins found in myelin--Nogo, MAG, and OMgp--inhibit axon regeneration in vitro and bind to the glycosylphosphatidylinositol-anchored Nogo receptor (NgR). However, genetic deletion of NgR has only a modest disinhibitory effect, suggesting that other binding receptors for these molecules probably exist. With the use of expression cloning, we have found that paired immunoglobulin-like receptor B (PirB), which has been implicated in nervous system plasticity, is a high-affinity receptor for Nogo, MAG, and OMgp. Interfering with PirB activity, either with antibodies or genetically, partially rescues neurite inhibition by Nogo66, MAG, OMgp, and myelin in cultured neurons. Blocking both PirB and NgR activities leads to near-complete release from myelin inhibition. Our results implicate PirB in mediating regeneration block, identify PirB as a potential target for axon regeneration therapies, and provide an explanation for the similar enhancements of visual system plasticity in PirB and NgR knockout mice.     

Enriched Pt-Re-Os isotope systematics in plume lavas explained by metasomatic sulfides

To explain the elevated osmium isotope (186Os-187Os) signatures in oceanic basalts, the possibility of material flux from the metallic core into the crust has been invoked. This hypothesis conflicts with theoretical constraints on Earth's thermal and dynamic history. To test the veracity and uniqueness of elevated 186Os-187Os in tracing core-mantle exchange, we present highly siderophile element analyses of pyroxenites, eclogites plus their sulfides, and new 186Os/188Os measurements on pyroxenites and platinum-rich alloys. Modeling shows that involvement in the mantle source of either bulk pyroxenite or, more likely, metasomatic sulfides derived from either pyroxenite or peridotite melts can explain the 186Os-187Os signatures of oceanic basalts. This removes the requirement for core-mantle exchange and provides an effective mechanism for generating Os isotope diversity in basalt source regions.     

Functional genomic analysis of RNA interference in C. elegans

RNA interference (RNAi) of target genes is triggered by double-stranded RNAs (dsRNAs) processed by conserved nucleases and accessory factors. To identify the genetic components required for RNAi, we performed a genome-wide screen using an engineered RNAi sensor strain of Caenorhabditis elegans. The RNAi screen identified 90 genes. These included Piwi/PAZ proteins, DEAH helicases, RNA binding/processing factors, chromatin-associated factors, DNA recombination proteins, nuclear import/export factors, and 11 known components of the RNAi machinery. We demonstrate that some of these genes are also required for germline and somatic transgene silencing. Moreover, the physical interactions among these potential RNAi factors suggest links to other RNA-dependent gene regulatory pathways.     

The structural basis of ribozyme-catalyzed RNA assembly

Life originated, according to the RNA World hypothesis, from self-replicating ribozymes that catalyzed ligation of RNA fragments. We have solved the 2.6 angstrom crystal structure of a ligase ribozyme that catalyzes regiospecific formation of a 5' to 3' phosphodiester bond between the 5'-triphosphate and the 3'-hydroxyl termini of two RNA fragments. Invariant residues form tertiary contacts that stabilize a flexible stem of the ribozyme at the ligation site, where an essential magnesium ion coordinates three phosphates. The structure of the active site permits us to suggest how transition-state stabilization and a general base may catalyze the ligation reaction required for prebiotic RNA assembly.     

Cryptosporidium and Giardia in locally harvested clams in Iqaluit,Nunavut

High prevalences of Cryptosporidium and Giardia were recently found in enteric illness patients in the Qikiqtaaluk region of Nunavut, Canada, with a foodborne, waterborne or animal source of parasites suspected. Clams (Mya truncata) are a commonly consumed, culturally important and nutritious country food in Iqaluit; however, shellfish may concentrate protozoan pathogens from contaminated waters. The goal of this work was to investigate clams as a potential source of Cryptosporidium and Giardia infections in residents in Iqaluit, Nunavut. The objectives were to estimate the prevalence and genetically characterize Cryptosporidium and Giardia in locally harvested clams. Clams (n = 404) were collected from Iqaluit harvesters in September 2016. Haemolymph (n = 328) and digestive gland (n = 390) samples were screened for Cryptosporidium and Giardia via PCR, and amplified products were further processed for sequence analyses for definitive confirmation. Giardia DNA was found in haemolymph from 2 clams, while Cryptosporidium was not detected. The two Giardia sequences were identified as zoonotic Giardia enterica assemblage B. The overall prevalence of Giardia in clams near Iqaluit was low (0.6%) compared with other studies in southern Canada and elsewhere. The presence of Giardia DNA in clams suggests human or animal faecal contamination of coastal habitat around Iqaluit in shellfish harvesting waters. Results from this study are intended to inform public health practice and planning in Inuit Nunangat.     

Impact-induced seismic activity on asteroid 433 Eros: a surface modification process

High-resolution images of the surface of asteroid 433 Eros revealed evidence of downslope movement of a loose regolith layer, as well as the degradation and erasure of small impact craters (less than approximately 100 meters in diameter). One hypothesis to explain these observations is seismic reverberation after impact events. We used a combination of seismic and geomorphic modeling to analyze the response of regolith-covered topography, particularly craters, to impact-induced seismic shaking. Applying these results to a stochastic cratering model for the surface of Eros produced good agreement with the observed size-frequency distribution of craters, including the paucity of small craters.