The growth of juvenile native mussels (Elliptio complanata) in lakes varies with sediment characteristics and site exposure

1. Unionid mussels are among the largest and longest-lived freshwater invertebrates and can play an important role in these ecosystems. They are also one of the most endangered groups of organisms. The juvenile stage is a particularly vulnerable part of mussel life history and is one of the most poorly known.
2. I compared the growth of young Elliptio complanata at 17 nearshore sites, in shallow (polymictic) and stratified lake basins, along gradients of sediment characteristics and site exposure (effective fetch). At each site, the growth of six to 14 small (20–68 mm) mussels collected on the sediment surface was measured, using internal growth lines. The growth of very young endobenthic mussels (22–40 mm) was also measured on four to six mussels at each of two sites.
3. Juveniles spend several years in the sediments, and I found that during this period growth is not constant but declines rapidly with age. Shifts in δ¹⁵N signatures suggest that juveniles change their habitat use towards a more planktonic baseline around the time of maturation, when they reach a length of 30–50 mm. Identical δ¹³C signatures in juveniles and adults suggest that both rely on food of planktonic origin, whether deposited or suspended.
4. The growth of juvenile mussels varies in a complex but predictable manner with sediment characteristics and wind-driven physical forces. Growth was highest in fine sediments with low organic content, in highly organic but coarse sediments, and in protected nearshore areas with low effective fetch. Interestingly, I also found high growth rates at exposed nearshore areas with fine sediments, suggesting that areas where bottom topography creates a refuge from currents and waves may provide particularly good conditions for the early growth of juvenile mussels.
5. Some parts of the shoreline may be more important than others for native mussel populations, and if we can identify those, they may warrant additional protection.

     

Interplay between protein homeostasis networks in protein aggregation and proteotoxicity

The misfolding and aggregation of disease proteins is characteristic of numerous neurodegenerative diseases. Particular neuronal populations are more vulnerable to proteotoxicity while others are more apt to tolerate the misfolding and aggregation of disease proteins. Thus, the cellular environment must play a significant role in determining whether disease proteins are converted into toxic or benign forms. The endomembrane network of eukaryotes divides the cell into different subcellular compartments that possess distinct sets of molecular chaperones and protein interaction networks. Chaperones act as agonists and antagonists of disease protein aggregation to prevent the accumulation of toxic intermediates in the aggregation pathway. Interacting partners can also modulate the conformation and localization of disease proteins and thereby influence proteotoxicity. Thus, interplay between these protein homeostasis network components can modulate the self‐association of disease proteins and determine whether they elicit a toxic or benign outcome. © 2009 Wiley Periodicals, Inc. Biopolymers 93: 229–236, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Plasma LH and androgen levels in the red-winged blackbird (Agelaius phoeniceus) treated with a potent GnRH analogue.

1. Low doses of GnRH-A (0.01-0.10-1.0 micrograms) given during the annual testes growth period did not clearly affect plasma LH and androgen levels 10 min following the injection. 2. The first injection of high doses of GnRH-A (2.0-10.0-20.0 micrograms) markedly increased plasma LH and androgen levels measured 10 min following the injection. The increase in plasma LH level was dose-dependent and the maximal LH level was obtained with 10.0 micrograms of GnRH-A. 3. Impairment of the LH response to GnRH-A was assessed by comparing the first and the fourteenth injection of high doses of GnRH-A. Evidences of pituitary gland desensitization are reported since plasma LH levels were reduced following the fourteenth injection in all groups. 4. Plasma androgen levels following high doses of GnRH-A were not clearly affected in red-winged blackbirds.     

Comparison of statistical methods for the analysis of limiting dilution assays

Summary This study reports the results of a critical comparison of five statistical methods for estimating the density of viable cells in a limiting dilution assay (LDA). Artificial data were generated using Monte Carlo simulation. The performance of each statistical method was examined with respect to the accuracy of its estimator and, most importantly, the accuracy of its associated estimated standard error (SE). The regression method was found to perform at a level that is unacceptable for scientific research, due primarily to gross underestimation of the SE. The maximum likelihood method exhibited the best overall performance. A corrected version of Taswell's weighted-mean method, which provides the best performance among all noniterative methods examined, is also presented.     

α,β-dicarbonyl reduction by Saccharomycesd-arabinose dehydrogenase

An α,β-dicarbonyl reductase activity was purified from Saccharomyces cerevisiae and identified as the cytosolic enzyme d-Arabinose dehydrogenase (ARA1) by MALDI-TOF/TOF. Size exclusion chromatography analysis of recombinant Ara1p revealed that this protein formed a homodimer. Ara1p catalyzed the reduction of the reactive α,β-dicarbonyl compounds methylglyoxal, diacetyl, and pentanedione in a NADPH dependant manner. Ara1p had apparent K_m values of ∼ 14 mM, 7 mM and 4 mM for methylglyoxal, diacetyl and pentanedione respectively, with corresponding turnover rates of 4.4, 6.9 and 5.9 s^− 1 at pH 7.0. pH profiling showed that Ara1p had a pH optimum of 4.5 for the diacetyl reduction reaction. Ara1p also catalyzed the NADP⁺ dependant oxidation of acetoin; however this back reaction only occurred at alkaline pH values. That Ara1p was important for degradation of α,β-dicarbonyl substrates was further supported by the observation that ara1-Δ knockout yeast mutants exhibited a decreased growth rate phenotype in media containing diacetyl.