Seasonality of chlorophyll and nutrients in Lake Erken – effects of weather conditions

The effect of submerged macrophytes on interactions among epilimnetic phosphorus, phytoplankton, and heterotrophic bacterioplankton has been acknowledged, but remains poorly understood. Here, we test the hypotheses that the mean summer phytoplankton biomass (chlorophyll a): phosphorus ratios decrease with increased macrophyte cover in a series of nine lakes. Further, we test that both planktonic respiration and bacterioplankton production increase with respect to phytoplankton biomass along the same gradient of increasing macrophyte cover. Increased macrophyte cover was associated with a lower fraction of particulate phosphorus in epilimnia, with total particulate phosphorus declining from over 80% of total phosphorus in a macrophyte free lake to less than 50% in a macrophyte rich lake. Phytoplankton biomass (chlorophyll a) too was lower in macrophyte dominated lakes, despite relatively high levels of total dissolved phosphorus. Planktonic respiration and bacterioplankton production were higher in macrophyte rich lakes than would be expected from phytoplankton biomass alone, pointing to a subsidy of bacterioplankton metabolism by macrophyte beds at the whole lake scale. The results suggest that the classical view of pelagic interactions, which proposes phosphorus determines phytoplankton abundance, which in turn determines bacterial abundance through the production of organic carbon, becomes less relevant as macrophyte cover increases.     

Regional Variability and Drivers of Below Ice CO<Subscript>2</Subscript> in Boreal and Subarctic Lakes

Northern lakes are ice-covered for considerable portions of the year, where carbon dioxide (CO₂) can accumulate below ice, subsequently leading to high CO₂ emissions at ice-melt. Current knowledge on the regional control and variability of below ice partial pressure of carbon dioxide (pCO₂) is lacking, creating a gap in our understanding of how ice cover dynamics affect the CO₂ accumulation below ice and therefore CO₂ emissions from inland waters during the ice-melt period. To narrow this gap, we identified the drivers of below ice pCO₂ variation across 506 Swedish and Finnish lakes using water chemistry, lake morphometry, catchment characteristics, lake position, and climate variables. We found that lake depth and trophic status were the most important variables explaining variations in below ice pCO₂ across the 506 lakes_. Together, lake morphometry and water chemistry explained 53% of the site-to-site variation in below ice pCO₂. Regional climate (including ice cover duration) and latitude only explained 7% of the variation in below ice pCO₂. Thus, our results suggest that on a regional scale a shortening of the ice cover period on lakes may not directly affect the accumulation of CO₂ below ice but rather indirectly through increased mobility of nutrients and carbon loading to lakes. Thus, given that climate-induced changes are most evident in northern ecosystems, adequately predicting the consequences of a changing climate on future CO₂ emission estimates from northern lakes involves monitoring changes not only to ice cover but also to changes in the trophic status of lakes.     

Breastfeeding and Its Prospective Association with Components of the GH-IGF-Axis,Insulin Resistance and Body Adiposity Measures in Young Adulthood – Insights from Linear and Quantile Regression Analysis

Background

Breastfeeding may lower chronic disease risk by long-term effects on hormonal status and adiposity, but the relations remain uncertain.

Objective

To prospectively investigate the association of breastfeeding with the growth hormone- (GH) insulin-like growth factor- (IGF) axis, insulin sensitivity, body composition and body fat distribution in younger adulthood (18–37 years).

Design

Data from 233 (54% female) participants of a German cohort, the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study, with prospective data on infant feeding were analyzed. Multivariable linear as well as quantile regression were performed with full breastfeeding (not: ≤2, short: 3–17, long: >17 weeks) as exposure and adult IGF-I, IGF binding proteins (IGFBP) -1, -2, -3, homeostasis model assessment of insulin resistance (HOMA-IR), fat mass index, fat-free mass index, and waist circumference as outcomes.

Results

After adjustment for early life and socio-economic factors, women who had been breastfed longer displayed higher adult IGFBP-2 (p_trend = 0.02) and lower values of HOMA-IR (p_trend = 0.004). Furthermore, in women breastfeeding duration was associated with a lower mean fat mass index (p_trend = 0.01), fat-free mass index (p_trend = 0.02) and waist circumference (p_trend = 0.004) in young adulthood. However, there was no relation to IGF-I, IGFBP-1 and IGFBP-3 (all p_trend>0.05). Associations for IGFBP-2 and fat mass index were more pronounced at higher, for waist circumference at very low or high percentiles of the distribution. In men, there was no consistent relation of breastfeeding with any outcome.

Conclusions

Our data suggest that breastfeeding may have long-term, favorable effects on extremes of adiposity and insulin metabolism in women, but not in men. In both sexes, breastfeeding does not seem to induce programming of the GH-IGF-axis.     

Peroxisome Proliferator-activated Receptor γ Coactivator 1α (PGC-1α) Promotes Skeletal Muscle Lipid Refueling in Vivo by Activating de Novo Lipogenesis and the Pentose Phosphate Pathway

Exercise induces a pleiotropic adaptive response in skeletal muscle, largely through peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α). PGC-1α enhances lipid oxidation and thereby provides energy for sustained muscle contraction. Its potential implication in promoting muscle refueling remains unresolved, however. Here, we investigated a possible role of elevated PGC-1α levels in skeletal muscle lipogenesis in vivo and the molecular mechanisms that underlie PGC-1α-mediated de novo lipogenesis. To this end, we studied transgenic mice with physiological overexpression of PGC-1α and human muscle biopsies pre- and post-exercise. We demonstrate that PGC-1α enhances lipogenesis in skeletal muscle through liver X receptor α-dependent activation of the fatty acid synthase (FAS) promoter and by increasing FAS activity. Using chromatin immunoprecipitation, we establish a direct interaction between PGC-1α and the liver X receptor-responsive element in the FAS promoter. Moreover, we show for the first time that increased glucose uptake and activation of the pentose phosphate pathway provide substrates for RNA synthesis and cofactors for de novo lipogenesis. Similarly, we observed increased lipogenesis and lipid levels in human muscle biopsies that were obtained post-exercise. Our findings suggest that PGC-1α coordinates lipogenesis, intramyocellular lipid accumulation, and substrate oxidation in exercised skeletal muscle in vivo.     

Syllis onkylochaeta sp. n., ein korallenfressender Polychaet (Syllidae) aus dem Korallenaquarium des Löbbecke-Museums

A new species of the genusSyllis is described feeding on a colony of corals of the genusXenia (Xeniidae, Alcyonaria) in the coral aquarium of the Löbbecke Museum Düsseldorf. The origin of the corals is very probably Bali (Indonesia).     

Fasergliastruktur der dorsalen Wand des Aquaeductus cerebri bei einigen Primaten

Zusammenfassung Bei Ateles, Cebus, Macaca und Pan wird die Architektonik der subependymalen Astroglia im ersten dorsalen Drittel des Aquaeductus cerebri und der marginalen Glia in der Commissura posterior und im Tectum beschrieben. Am Dach des Aquaeductus cerebri sind regionale Unterschiede in der subependymalen Fasertextur zu erkennen; den einzelnen Regionen entsprechen bestimmte Gliazelltypen. Verschiedenheiten zeigt auch die Anordnung der marginalen Glia der Commissura posterior und des Tectum. Zwischen der subependymalen Gliafaserdeckschicht des Subcommissuralorgans bzw. des Recessus mesocoelicus und der marginalen Glia der Commissura posterior besteht ein direkter Strukturzusammenhang. Diesen vermitteln kräftige perivasculäre Radiärfaserbündel, an die sich z.T. auch noch bipolare Tanycytenformen (Recessus mesocoelicus) anschließen. Zwischen der subependymalen Gliafaserdeckschicht des Aquaeductus cerebri und der marginalen Glia des Tectum läßt sich dagegen keine direkte Verbindung nachweisen. Eine mechanische (statische) Funktion der in der vorliegenden und in einer früheren Studie (Merker, 1968) beobachteten Gliatexturen wird diskutiert.

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The structure of fibrous astroglia in the dorsal wall of the cerebral aqueduct in some primates

Summary The structure and architecture of the subependymal astrocytes of the first third of the roof of the cerebral aqueduct and the marginal glia of the posterior commissure and of the tectum were studied in Ateles, Cebus, Macaca, and Pan. Regional differences in the types of subependymal astrocytes were observed in the roof of the cerebral aqueduct. The marginal glia of the posterior commissure and of the tectum also had special structural patterns. A direct structural connexion was found to exist between the subependymal glial layer of the subcommissural complex, or the recessus mesocoelicus, and the marginal glia of the posterior commissure. The connexion was characterized by coarse radial perivascular fiber bundles, supported to some extent by bipolar gliocytes. No junctional arrangement, however, was seen between the subependymal fiber layer of the cerebral aqueduct and the marginal fibrous glia of the tectum. The observations suggested that the astroglial formations may have a mechanical function.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Trisomy of human chromosome 18: Molecular studies on parental origin and cell stage of nondisjunction

We investigated the parent and cell division of origin of the extra chromosome 18 in 62 aneuploids with a free trisomy 18 by using chromosome-18-specific pericentromeric short-sequence repeats. In 46 cases, DNA of patients was recovered from archival specimens, such as paraffin-embedded tissues and fixed chromosomal spreads. In 56 families, the supernumerary chromosome was maternal in origin; in six families, it was paternal. Among the 56 maternally derived aneuploids, we could exclude a postzygotic mitotic error in 52 cases. Among those in which the nondisjunction was attributable to an error at meiosis, 11 were the result of a meiosis I nondisjunction and 17 were caused by a meiosis II error. This result differs markedly from findings in acrocentric chromosomes where nondisjunction at maternal meiosis I predominates. Among the six paternally derived cases, two originated from a meiotic error, indicating that a nondisjunction in paternal meiosis is not as rare as previously suggested.Dedicated to Professor Dr. W. Gottschalk on the occasion of his 75th birthday     

Early remodelling of the extracellular matrix proteins tenascin‐C and phosphacan in retina and optic nerve of an experimental autoimmune glaucoma model

Glaucoma is characterized by the loss of retinal ganglion cells (RGCs) and optic nerve fibres. Previous studies noted fewer RGCs after immunization with ocular antigens at 28 days. It is known that changes in extracellular matrix (ECM) components conduct retina and optic nerve degeneration. Here, we focused on the remodelling of tenascin‐C and phosphacan/receptor protein tyrosine phosphatase β/ζ in an autoimmune glaucoma model. Rats were immunized with optic nerve homogenate (ONA) or S100B protein (S100). Controls received sodium chloride (Co). After 14 days, no changes in RGC number were noted in all groups. An increase in GFAP mRNA expression was observed in the S100 group, whereas no alterations were noted via immunohistochemistry in both groups. Extracellular matrix remodelling was analyzed after 3, 7, 14 and 28 days. Tenascin‐C and 473HD immunoreactivity in retinae and optic nerves was unaltered in both immunized groups at 3 days. At 7 days, tenascin‐C staining increased in both tissues in the ONA group. Also, in the optic nerves of the S100 group, an intense tenascin‐C staining could be shown. In the retina, an increased tenascin‐C expression was also observed in ONA animals via Western blot. 473HD immunoreactivity was elevated in the ONA group in both tissues and in the S100 optic nerves at 7 days. At 14 days, tenascin‐C and 473HD immunoreactivity was up‐regulated in the ONA retinae, whereas phosphacan expression was up‐regulated in both groups. We conclude that remodelling of tenascin‐C and phosphacan occurred shortly after immunization, already before RGC loss. We assume that both ECM molecules represent early indicators of neurodegeneration.