Stable isotope fractionation by phytoplankton in response to daylength, growth rate, and CO2 availability

Stable carbon isotope fractionation (ε p) of 7 marine phytoplankton species grown in different irradiance cycles was measured under nutrient-replete conditions at a high light intensity in batch cultures. Compared to experiments under continuous light, all species exhibited a significantly higher instantaneous growth rate (μi), defined as the rate of carbon fixation during the photoperiod, when cultivated at 12:12 h, 16:8 h, or 18:6 h light:dark (L/D) cycles. Isotopic fractionation by the diatoms Skeletonema costatum, Asterionella glacialis, Thalassiosira punctigera, and Coscinodiscus wailesii (Group I) was 4 to 6o/oo lower in a 16:8 h L/D cycle than under continuous light, which we attribute to differences in μi. In contrast, ε p in Phaeodactylum tricornutum, Thalassiosira weissflogii, and in the dinoflagellate Scrippsiella trochoidea (Group II) was largely insensitive to daylength-related differences in instantaneous growth rate. Since other studies have reported growth-rate dependent fractionation under N-limited conditions in P. tricornutum, μi-related effects on fractionation apparently depend on the factor controlling growth rate. We suggest that a general relationship between εi and μi/[CO2,aq] may not exist. For 1 species of each group we tested the effect of variable CO2 concentration, [CO2,aq], on isotopic fractionation. A decrease in [CO2,aq] from ca 26 to 3 µmol kg-1 caused a decrease in ε p by less than 3o/oo. This indicates that variation in μi in response to changes in daylength has a similar or even greater effect on isotopic fractionation than [CO2,aq] in some of the species tested. In both groups ε p tended to be higher in smaller species at comparable growth rates. In 24 and 48 h time series the algal cells became progressively enriched in 13C during the day and the first hours of the dark period, followed by 13C depletion in the 2 h before beginning of the following light period. The daily amplitude of the algal isotopic composition (δ13C), however, was <=1.5o/oo, which demonstrates that diurnal variation in δ13C is relatively small

Large-scale meta-analysis highlights the hypothalamic–pituitary–gonadal axis in the genetic regulation of menstrual cycle length

The normal menstrual cycle requires a delicate interplay between the hypothalamus, pituitary and ovary. Therefore, its length is an important indicator of female reproductive health. Menstrual cycle length has been shown to be partially controlled by genetic factors, especially in the follicle-stimulating hormone beta-subunit (FSHB) locus. A genome-wide association study meta-analysis of menstrual cycle length in 44 871 women of European ancestry confirmed the previously observed association with the FSHB locus and identified four additional novel signals in, or near, the GNRH1, PGR, NR5A2 and INS-IGF2 genes. These findings not only confirm the role of the hypothalamic–pituitary–gonadal axis in the genetic regulation of menstrual cycle length but also highlight potential novel local regulatory mechanisms, such as those mediated by IGF2

Decreasing marine biogenic calcification: a negative feedback on rising atmospheric pCO2

In laboratory experiments with the coccolithophore species Emiliania huxleyi and Gephyrocapsa oceanica, the ratio of particulate inorganic carbon (PIC) to particulate organic carbon (POC) production decreased with increasing CO2 concentration ([CO2]). This was due to both reduced PIC and enhanced POC production at elevated [CO2]. Carbon dioxide concentrations covered a range from a preindustrial level to a value predicted for 2100 according to a “business as usual” anthropogenic CO2 emission scenario. The laboratory results were used to employ a model in which the immediate effect of a decrease in global marine calcification relative to POC production on the potential capacity for oceanic CO2 uptake was simulated. Assuming that overall marine biogenic calcification shows a similar response as obtained for E. huxleyi or G. oceanica in the present study, the model reveals a negative feedback on increasing atmospheric CO2 concentrations owing to a decrease in the PIC/POC ratio

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

Genome-wide association identifies nine common variants associated with fasting proinsulin levels and provides new insights into the pathophysiology of type 2 diabetes.

OBJECTIVE: Proinsulin is a precursor of mature insulin and C-peptide. Higher circulating proinsulin levels are associated with impaired β-cell function, raised glucose levels, insulin resistance, and type 2 diabetes (T2D). Studies of the insulin processing pathway could provide new insights about T2D pathophysiology. RESEARCH DESIGN AND METHODS: We have conducted a meta-analysis of genome-wide association tests of ∼2.5 million genotyped or imputed single nucleotide polymorphisms (SNPs) and fasting proinsulin levels in 10,701 nondiabetic adults of European ancestry, with follow-up of 23 loci in up to 16,378 individuals, using additive genetic models adjusted for age, sex, fasting insulin, and study-specific covariates. RESULTS: Nine SNPs at eight loci were associated with proinsulin levels (P < 5 × 10(-8)). Two loci (LARP6 and SGSM2) have not been previously related to metabolic traits, one (MADD) has been associated with fasting glucose, one (PCSK1) has been implicated in obesity, and four (TCF7L2, SLC30A8, VPS13C/C2CD4A/B, and ARAP1, formerly CENTD2) increase T2D risk. The proinsulin-raising allele of ARAP1 was associated with a lower fasting glucose (P = 1.7 × 10(-4)), improved β-cell function (P = 1.1 × 10(-5)), and lower risk of T2D (odds ratio 0.88; P = 7.8 × 10(-6)). Notably, PCSK1 encodes the protein prohormone convertase 1/3, the first enzyme in the insulin processing pathway. A genotype score composed of the nine proinsulin-raising alleles was not associated with coronary disease in two large case-control datasets. CONCLUSIONS: We have identified nine genetic variants associated with fasting proinsulin. Our findings illuminate the biology underlying glucose homeostasis and T2D development in humans and argue against a direct role of proinsulin in coronary artery disease pathogenesis

Light-dependent carbon isotope fractionation in the coccolithophorid Emiliania huxleyi

The carbon isotopic composition of marine phytoplankton varies significantly with growth conditions. Aqueous CO2 concentration [CO2] and algal growth rate (µ) have been suggested to be important factors determining isotope fractionation (ep). Here we examine ep of the coccolithophorid Emiliania huxleyi in relation to CO2 concentration and light conditions in dilute batch cultures. Cells were incubated at different irradiance cycles, photon flux densities (PFDs), and [CO2]. Isotope fractionation varied between 6.7 and 12.3‰ under 16 : 8 h light : dark cycle (L :D) and between 14.7 and 17.8‰ at continuous light. ep was largely independent of ambient [CO2], varying generally by less than 2‰ over a range of [CO2] from 5 to 34 mmol L-1. Instantaneous carbon-specific growth rates (µC) and PFDs, ranging from 15 to 150 mmol m-2 s-1, positively correlated with ep. This result is inconsistent with theoretical considerations and experimental results obtained under constant light conditions, suggesting an inverse relationship between ep and µ. In the present study the effect of PFDs on ep was stronger than that of mand thus resulted in a positive relationship between µ and ep. In addition, the L:D cycle of 16 : 8 h resulted in significantly lower ep values compared to continuous light. Since the observed offset of about 8‰ could not be related to daylength dependent changes in µC, this implies a direct influence of the irradiance cycle on ep. These findings are best explained by invoking active carbon uptake in E. huxleyi. If representative for the natural environment, these results complicate the interpretation of carbon isotope data in geochemical and paleoceanographic applications