Ion Permeabilities in Mouse Sperm Reveal an External Trigger for SLO3-Dependent Hyperpolarization

Unlike most cells of the body which function in an ionic environment controlled within narrow limits, spermatozoa must function in a less controlled external environment. In order to better understand how sperm control their membrane potential in different ionic conditions, we measured mouse sperm membrane potentials under a variety of conditions and at different external K⁺ concentrations, both before and after capacitation. Experiments were undertaken using both wild-type, and mutant mouse sperm from the knock-out strain of the sperm-specific, pH-sensitive, SLO3 K⁺ channel. Membrane voltage data were fit to the Goldman-Hodgkin-Katz equation. Our study revealed a significant membrane permeability to both K⁺ and Cl⁻ before capacitation, as well as Na⁺. The permeability to both K⁺ and Cl⁻ has the effect of preventing large changes in membrane potential when the extracellular concentration of either ion is changed. Such a mechanism may protect against undesired shifts in membrane potential in changing ionic environments. We found that a significant portion of resting membrane potassium permeability in wild-type sperm was contributed by SLO3 K⁺ channels. We also found that further activation of SLO3 channels was the essential mechanism producing membrane hyperpolarization under two separate conditions, 1) elevation of external pH prior to capacitation and 2) capacitating conditions. Both conditions produced a significant membrane hyperpolarization in wild-type which was absent in SLO3 mutant sperm. Hyperpolarization in both conditions may result from activation of SLO3 channels by raising intracellular pH; however, demonstrating that SLO3-dependent hyperpolarization is achieved by an alkaline environment alone shows that SLO3 channel activation might occur independently of other events associated with capacitation. For example sperm may undergo stages of membrane hyperpolarization when reaching alkaline regions of the female genital tract. Significantly, other events associated with sperm capacitation, occur in SLO3 mutant sperm and thus proceed independently of hyperpolarization.     

ECOPHYSIOLOGY OF TROPICAL RHODOPHYTES. I. MICROSCALE ACCLIMATION IN PIGMENTATION1,2

Microscale pigment adjustments to a tropical photosynthetically active radiation and ultraviolet (UV) environment by the intertidal turf algae Ahnfeltiopsis concinna (J. Ag.) Silva et DeCew and Laurencia mcdermidiae (J. Ag) Abbott were promoted by thalli densities that self-shade the under story portions of the same diminutive axes. Tissues of A. concinna from canopy microsites had significantly reduced levels of phycoerythrin, phycocyanin, and allophycocyanin compared to tissues from understory microsites of the same axes. Tissues of L. mcdermidiae from canopy microsites had reduced levels of only phycoerythrin compared to tissues from understory microsites. These alterations coupled with enhanced levels of carotenoid and UV-absorbing compounds in tissues from canopy compared to tissues from understory microsites indicated a pattern of remarkably sensitive photoacclimation over the ≤10-cm axes of these turf-forming rhodophytes. Microscale variation in the in vivo UV absorbance capabilities for turfs of A. concinna and L. mcdermidiae was directly related to the amount of extractable UV-absorbing compounds. An in vivo absorbance signature at ～345 nm appears to provide a method to quickly and accurately gauge the potential UV-shielding capacity of primary producers even at remarkably fine ecological scales. The capacity for highly responsive biochemical adjustments that result in marked canopy–understory distinctions coupled with a turf morphology may be crucial for macroalgal tolerance of physiological stresses associated with tropical intertidal zones. This responsive capacity allows for enhanced photoprotective mechanisms in tissues from canopy microsites while optimizing irradiance capture in deeply shaded tissues from understory microsites < 10 cm away.     

Functional microbiome deficits associated with ageing: Chronological age threshold

Composition of the gut microbiota changes during ageing, but questions remain about whether age is also associated with deficits in microbiome function and whether these changes occur sharply or progressively. The ability to define these deficits in populations of different ages may help determine a chronological age threshold at which deficits occur and subsequently identify innovative dietary strategies for active and healthy ageing. Here, active gut microbiota and associated metabolic functions were evaluated using shotgun proteomics in three well‐defined age groups consisting of 30 healthy volunteers, namely, ten infants, ten adults and ten elderly individuals. Samples from each volunteer at intervals of up to 6 months (n = 83 samples) were used for validation. Ageing gradually increases the diversity of gut bacteria that actively synthesize proteins, that is by 1.4‐fold from infants to elderly individuals. An analysis of functional deficits consistently identifies a relationship between tryptophan and indole metabolism and ageing (p < 2.8e^?8). Indeed, the synthesis of proteins involved in tryptophan and indole production and the faecal concentrations of these metabolites are directly correlated (r² > .987) and progressively decrease with age (r² > .948). An age threshold for a 50% decrease is observed ca. 11–31 years old, and a greater than 90% reduction is observed from the ages of 34–54 years. Based on recent investigations linking tryptophan with abundance of indole and other “healthy” longevity molecules and on the results from this small cohort study, dietary interventions aimed at manipulating tryptophan deficits since a relatively “young” age of 34 and, particularly, in the elderly are recommended.     

PEATmoss (Physcomitrella Expression Atlas Tool): a unified gene expression atlas for the model plant Physcomitrella patens

Physcomitrella patens is a bryophyte model plant that is often used to study plant evolution and development. Its resources are of great importance for comparative genomics and evo‐devo approaches. However, expression data from Physcomitrella patens were so far generated using different gene annotation versions and three different platforms: CombiMatrix and NimbleGen expression microarrays and RNA sequencing. The currently available P. patens expression data are distributed across three tools with different visualization methods to access the data. Here, we introduce an interactive expression atlas, Physcomitrella Expression Atlas Tool (PEATmoss), that unifies publicly available expression data for P. patens and provides multiple visualization methods to query the data in a single web‐based tool. Moreover, PEATmoss includes 35 expression experiments not previously available in any other expression atlas. To facilitate gene expression queries across different gene annotation versions, and to access P. patens annotations and related resources, a lookup database and web tool linked to PEATmoss was implemented. PEATmoss can be accessed at https://peatmoss.online.uni-marburg.de     

Sierra Nevada mountain lake microbial communities are structured by temperature,resources and geographic location

Warming, eutrophication (nutrient fertilization) and brownification (increased loading of allochthonous organic matter) are three global trends impacting lake ecosystems. However, the independent and synergistic effects of resource addition and warming on autotrophic and heterotrophic microorganisms are largely unknown. In this study, we investigate the independent and interactive effects of temperature, dissolved organic carbon (DOC, both allochthonous and autochthonous) and nitrogen (N) supply, in addition to the effect of spatial variables, on the composition, richness, and evenness of prokaryotic and eukaryotic microbial communities in lakes across elevation and N deposition gradients in the Sierra Nevada mountains of California, USA. We found that both prokaryotic and eukaryotic communities are structured by temperature, terrestrial (allochthonous) DOC and latitude. Prokaryotic communities are also influenced by total and aquatic (autochthonous) DOC, while eukaryotic communities are also structured by nitrate. Additionally, increasing N availability was associated with reduced richness of prokaryotic communities, and both lower richness and evenness of eukaryotes. We did not detect any synergistic or antagonistic effects as there were no interactions among temperature and resource variables. Together, our results suggest that (a) organic and inorganic resources, temperature, and geographic location (based on latitude and longitude) independently influence lake microbial communities; and (b) increasing N supply due to atmospheric N deposition may reduce richness of both prokaryotic and eukaryotic microbes, probably by reducing niche dimensionality. Our study provides insight into abiotic processes structuring microbial communities across environmental gradients and their potential roles in material and energy fluxes within and between ecosystems.