Carbonic anhydrase seven bundles filamentous actin and regulates dendritic spine morphology and density

Intracellular pH is a potent modulator of neuronal functions. By catalyzing (de)hydration of CO₂, intracellular carbonic anhydrase (CA_i) isoforms CA2 and CA7 contribute to neuronal pH buffering and dynamics. The presence of two highly active isoforms in neurons suggests that they may serve isozyme‐specific functions unrelated to CO₂‐(de)hydration. Here, we show that CA7, unlike CA2, binds to filamentous actin, and its overexpression induces formation of thick actin bundles and membrane protrusions in fibroblasts. In CA7‐overexpressing neurons, CA7 is enriched in dendritic spines, which leads to aberrant spine morphology. We identified amino acids unique to CA7 that are required for direct actin interactions, promoting actin filament bundling and spine targeting. Disruption of CA7 expression in neocortical neurons leads to higher spine density due to increased proportion of small spines. Thus, our work demonstrates highly distinct subcellular expression patterns of CA7 and CA2, and a novel, structural role of CA7.     

Identification of UEA I-binding surface glycoproteins of cultured human endothelial cells

Ulex europaeus agglutinin (UEAI) binds mainly to endothelial cells in human tissues. In cultured human umbilical vein endothelial cells TRITC-UEAI gave an even surface staining but no binding to pericellular material. After permeabilization of the cells UEAI decorated the Golgi apparatus as a juxtanuclear structure. Electrophoresis of Triton X-100 lysates of 35S-methionine labeled cells bound to lectin agarose beads showed that a similar set of polypeptides was recognized by UEA-I and WGA while distinctly different polypeptides were bound to LcA-agarose. Surface labelling revealed major glycoproteins with Mr 220 kD, 160 kD, 140 kD, 120 kD, 80 kD and 50 kD, most of which could be extracted with Triton X-100. However, only the 140 kD gp, 120 kD gp and 80 kD gp showed binding to UEA 140 kD gp, 120 kD gp and 80 kD gp showed binding to UEA I-lectin. The results show that among a distinct set of surface glycoproteins in cultured human endothelial cells only a few have alpha-l-fucosyl moieties capable of binding to UEAI lectin.     

Molecular lineage diversity and inter‐oceanic biogeographical history in Hiatella (Mollusca,Bivalvia)

Hiatella is one of the most widespread marine bivalve genera, occurring in diverse habitats from the temperate to polar latitudes in both hemispheres, and in fossil strata since almost 150 Myr ago. Despite variation in some biological and morphological traits, characters to resolve the current systematic structure consistently across the range of the genus are not known: all samples are often referred to a single species, Hiatella arctica (L.). Exploring the systematics of Hiatella using partial sequences of three genes (mitochondrial COI, and the nuclear ANT and 28S rRNA), we find high diversity of deep lineages (11–22% p‐distance in COI), and identify at least 13 distinct taxa both by heuristic criteria (congruence of the nuclear and mtDNA data) and by coalescence‐based analyses. At several localities, two or three of these cryptic species were found in sympatry. In the framework of previous fossil evidence and of hypotheses of paleoceanographical connections, scenarios of the phylogeny and biogeographical history of the identified species at a range of different time scales are outlined. The distinction between the main North Pacific and North Atlantic Hiatella clades and systematic diversification within each of them seem to have followed a Miocene trans‐Panamanian invasion. Apart from such earlier intra‐basin diversification, the data suggest that three successive counter‐invasions from the Pacific to the Atlantic via the Arctic Ocean route have later contributed to the current North Atlantic Hiatella diversity. These invasions probably took place in connection with (i) the Great Trans‐Arctic Biotic Interchange in the Pliocene, (ii) the last interglacial period c. 120 kya and (iii) the Holocene, postdating the last glaciation. This sequence of trans‐Arctic invasions is largely analogous to that hypothesized for some other boreal‐arctic bivalves.     

Contractile proteins and nonerythroid spectrin in the oogenesis of the clawed toad]

Distribution of contractile proteins, actin and myosin, and spectrin was studied in oogenesis of X. laevis. These proteins are present already at the previtellogenic stages, where they are diffusely distributed. During vitellogenesis actin and myosin are distributed in the animal region in a fibril-like way, while in the vegetal one they are concentrated around the yolk platelets. In the mature oocyte, distribution of actin and myosin again becomes diffuse. Spectrin forms in the vitellogenic oocyte a network all over the cytoplasm, while in the full-grown oocyte it is localized mostly in the subcortex of the animal region and disappears during oocyte maturation. All these proteins are present in the nuclei of oocytes. Changes in distribution of actin, myosin and spectrin during oocyte maturation are discussed with reference to the cortical contractility, spatial distribution of yolk platelets and regional sensitivity to cytochalasin B.     

High focus on threatened species and habitats may undermine biodiversity conservation: Evidence from the northern Baltic Sea

Conservation policies and environmental impact assessments commonly target threatened species and habitats. Nevertheless, macroecological research provides reasons why also common species should be considered. We investigate the consequences of focussing solely on legally protected species and habitats in a spatial conservation planning context using a comprehensive, benthic marine data set from the northern Baltic Sea. Using spatial prioritization and surrogacy analysis, we show that the common approach in conservation planning, where legally listed threatened species and habitats are the focus of conservation efforts, could lead to poor outcomes for common species (and therefore biodiversity as a whole), allowing them to decline in the future. If conservation efforts were aimed solely at threatened species, common species would experience a loss of 62% coverage. In contrast, if conservation plans were based only on common species, threatened species would suffer a loss of 1%. Threatened species are rare and their ecological niches distinct, making them poor surrogates for biodiversity. The best results are achieved by unified planning for all species and habitats. The minimal step towards acknowledging common species in conservation planning would be the inclusion of the richness of common species, complemented by information on indicator species or species of high importance for ecosystem functioning. The trade-off between planning for rare and common species should be evaluated, to minimize losses to biodiversity.     

Drivers of the microbial metabolic quotient across global grasslands

Aim

The microbial metabolic quotient (MMQ; mg CO₂-C/mg MBC/h), defined as the amount of microbial CO₂ respired (MR; mg CO₂-C/kg soil/h) per unit of microbial biomass C (MBC; mg C/kg soil), is a key parameter for understanding the microbial regulation of the carbon (C) cycle, including soil C sequestration. Here, we experimentally tested hypotheses about the individual and interactive effects of multiple nutrient addition (nitrogen + phosphorus + potassium + micronutrients) and herbivore exclusion on MR, MBC and MMQ across 23 sites (five continents). Our sites encompassed a wide range of edaphoclimatic conditions; thus, we assessed which edaphoclimatic variables affected MMQ the most and how they interacted with our treatments.

Location

Australia, Asia, Europe, North/South America.

Time period

2015–2016.

Major taxa

Soil microbes.

Methods

Soils were collected from plots with established experimental treatments. MR was assessed in a 5-week laboratory incubation without glucose addition, MBC via substrate-induced respiration. MMQ was calculated as MR/MBC and corrected for soil temperatures (MMQsoil). Using linear mixed effects models (LMMs) and structural equation models (SEMs), we analysed how edaphoclimatic characteristics and treatments interactively affected MMQsoil.

Results

MMQsoil was higher in locations with higher mean annual temperature, lower water holding capacity and lower soil organic C concentration, but did not respond to our treatments across sites as neither MR nor MBC changed. We attributed this relative homeostasis to our treatments to the modulating influence of edaphoclimatic variables. For example, herbivore exclusion, regardless of fertilization, led to greater MMQsoil only at sites with lower soil organic C (< 1.7%).

Main conclusions

Our results pinpoint the main variables related to MMQsoil across grasslands and emphasize the importance of the local edaphoclimatic conditions in controlling the response of the C cycle to anthropogenic stressors. By testing hypotheses about MMQsoil across global edaphoclimatic gradients, this work also helps to align the conflicting results of prior studies.     

Selective extraction of hemicelluloses from spruce using switchable ionic liquids

Switchable ionic liquids (SILs) made from alcohols, either hexanol or butanol, and CO₂ together with an amidine (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)) were investigated as dissolution/fractionation solvents for wood material. Both native spruce (Picea abies), and pre-extracted spruce were treated with either butanol SIL (SIL1) or hexanol SIL (SIL2) for 5 days at 55 °C under normal pressure. The SILs were formed by bubbling CO₂ through an equimolar mixture of either 1-hexanol or 1-butanol and DBU. The viscosity of the mixture increased from 7.1 mPa s to 2980 mPa s for SIL2 and 5.1 to 1600 mPa s for SIL1. Melting points of the SILs 1 and 2 were at 8 and 14 °C, respectively. After the treatment time (5 days), the undissolved fraction contained 38 wt.% less hemicelluloses compared to native spruce. There was an increase in the glucose content of the milled spruce treated with both SILs, since the milling step reduced the cellulose crystallinity of the wood and facilitated an easier SIL access into the wood. The solvents were very neutral in terms of lignin removal. Consequently, only about 2% of the lignin was removed from native wood. Moreover, a priori removal of the wood extractives did not influence the lignin removal.