Climate change and seasonal reproduction in mammals

Seasonal reproduction is common among mammals at all latitudes, even in the deep tropics. This paper (i) discusses the neuroendocrine pathways via which foraging conditions and predictive cues such as photoperiod enforce seasonality, (ii) considers the kinds of seasonal challenges mammals actually face in natural habitats, and (iii) uses the information thus generated to suggest how seasonal reproduction might be influenced by global climate change. Food availability and ambient temperature determine energy balance, and variation in energy balance is the ultimate cause of seasonal breeding in all mammals and the proximate cause in many. Photoperiodic cueing is common among long-lived mammals from the highest latitudes down to the mid-tropics. It is much less common in shorter lived mammals at all latitudes. An unknown predictive cue triggers reproduction in some desert and dry grassland species when it rains. The available information suggests that as our climate changes the small rodents of the world may adapt rather easily but the longer lived mammals whose reproduction is regulated by photoperiod may not do so well. A major gap in our knowledge concerns the tropics; that is where most species live and where we have the least understanding of how reproduction is regulated by environmental factors.     

Male aggression,limited female choice and the ontogeny of mating behaviour in the flesh fly Sarcophaga crassipalpis

Previous work has shown that male flesh flies (Sarcophaga crassipalpis Macquart) exhibit an ontogeny of behaviour from eclosion through sexual maturity that includes extensive changes in the expression of aggressive, non‐aggressive interactive and non‐interactive behaviours. To determine how the presence of a female flesh fly influences the manifestation of these behaviours, male flesh flies of different ages post‐eclosion are paired with same‐age females and their behaviours are monitored in a simple arena during a 50‐min observation period. All flies are socially isolated until pairing. Although the levels of expression of aggressive and non‐aggressive interactive behaviours are depressed relative to previous findings in male‐opponent pairs, the ontogeny of aggression still occurs as indicated by a significant increase, with age, in the agonistic behaviour ‘hold’. Similar to male‐opponent pairs and individual males, the performance by males of the non‐interactive behaviours ‘walking’ and ‘standing’ diminishes, whereas ‘upside‐down’ increases with age. By contrast, ‘grooming’ shows a significant age‐related decline. No courtship behaviours are observed in the males, although the aggressive behaviour ‘hold’ is a significant transition to mating. Females show no obvious courtship or rejection behaviours, although the significant increase in ‘upside‐down’ with age could possibly be a behavioural gateway to mating. The results of this study indicate that extensive age‐related changes encompassing the entire behavioural repertoire are intrinsic to male flesh flies and persist under a variety of different social contexts.     

Carbon emissions performance of commercial logging in East Kalimantan,Indonesia

Adoption of reduced‐impact logging (RIL) methods could reduce CO₂ emissions by 30–50% across at least 20% of remaining tropical forests. We developed two cost effective and robust indices for comparing the climate benefits (reduced CO₂ emissions) due to RIL. The indices correct for variability in the volume of commercial timber among concessions. We determined that a correction for variability in terrain slope was not needed. We found that concessions certified by the Forest Stewardship Council (FSC, N = 3), when compared with noncertified concessions (N = 6), did not have lower overall CO₂ emissions from logging activity (felling, skidding, and hauling). On the other hand, FSC certified concessions did have lower emissions from one type of logging impact (skidding), and we found evidence of a range of improved practices using other field metrics. One explanation of these results may be that FSC criteria and indicators, and associated RIL practices, were not designed to achieve overall emissions reductions. Also, commonly used field metrics are not reliable proxies for overall logging emissions performance. Furthermore, the simple distinction between certified and noncertified concessions does not fully represent the complex history of investments in improved logging practices. To clarify the relationship between RIL and emissions reductions, we propose the more explicit term ‘RIL‐C’ to refer to the subset of RIL practices that can be defined by quantified thresholds and that result in measurable emissions reductions. If tropical forest certification is to be linked with CO₂ emissions reductions, certification standards need to explicitly require RIL‐C practices.     

Kinetic β-deuterium isotope effects suggest a covalent mechanism for the protein folding enzyme peptidylprolyl cis/trans-isomerase

The cis/trans interconversion of Glt-Ala-Ala-Pro-Phe-4-nitroanilide and Glt-Ala-Gly-Pro-Phe-4-nitroanilide was studied both enzymatically and nonenzymatically by measuring kinetic β-deuterium isotope effects. The hydrogen atom at the α-carbon atom of the Xaa residue within the Xaa-Pro moiety was substituted by deuterium. In the nonenzymatic case the transition state of rotation is reflected by k_H/k_D > 1. When catalysed by 17 kDa PPIase the same bond rotation is characterized by k_H/k_D < 1. This suggests a covalent mechanism of catalysis which involves an approximately tetravalent carbon of the prolyl imidic bond for the transition state of reaction.     

Interaction of alpha-N-Acetyl-beta-endorphin and calmodulin

Acetylation at the -amino terminal is a common post-translational modification of many peptides and proteins. In the case of the potent opiate peptide -endorphin, -N-acetylation is a known physiological modification that abolishes opiate activity. Since there are no known receptors for -N-acetyl--endorphin, we have studied the association of this peptide with calmodulin, a calcium-dependent protein that binds a variety of peptides, phenothiazines, and enzymes, as a model system for studying acetylated endorphin-protein interactions. Association of the acetylated peptide with calmodulin was demonstrated by cross-linking with bis(sulfosuccinimidyl)suberate; like -endorphin, adducts containing 1 mol and 2 mol of acetylated peptide per mole calmodulin were formed. Some of the bound peptides are evidently in relatively close proximity to each other since, in the presence of amidated (i.e., lysine-blocked) calmodulin, cross-linking yielded peptide dimers. The acetylated peptide exhibited no appreciable helicity in aqueous solution, but in trifluoroethanol (TFE) considerable helicity was formed. Also, a mixture of acetylated peptide and calmodulin was characterized by a circular dichroic spectrum indicative of induced helicity. Empirical prediction rules, applied earlier to -endorphin, suggest that residues 14–24 exhibit -helix potential. This segment has the potential of forming an amphipathic helix; this structural unit is believed to be important in calmodulin binding. The acetylated peptide was capable of inhibiting the calmodulin-mediated stimulation of cyclic nucleotide phosphodiesterase (EC 3.1.4.17) activity with an effective dose for 50% inhibition of about 3 µM; this inhibitory effect was demonstrated using both an enzyme-enriched preparation as well as highly purified enzyme. Thus, acetylation at the -amino terminal of -endorphin, although abolishing opiate activity, does not interfere with the binding to calmodulin. Indeed, -endorphin and the -N-acetylated peptide behave very similarly with respect to calmodulin association.Portions of this work are in partial fulfillment of the requirements for the Ph.D. degree from Vanderbilt University.     

Secretion and export of IGF-1 in Escherichia coli strain JM101

Summary The processing of LamB-IGF-1 fusion protein and the export of processed IGF-1 (insulin-like growth-factor-1) into the growth medium was examined in the Escherichia coli host strain, JM101. Several strain or plasmid modifications were tried to increase export of periplasmic (Processed) IGF-1 into the growth medium of JM101. These included: (1) use of a lon null mutant strain to increase accumulation levels of unprocessed LamB-IGF-1 fusion protein; (2) use of an alternative drug resistance marker on the expression plasmid rather than beta-lactamase, thereby reducing any competition for processing of LamB-IGF-1 by signal peptidase; (3) examination of whether phage M13 gene III protein expression caused more periplasmic IGF-1 to be exported into the growth medium due to increased outer membrane permeability; and (4) examination of the effect of E. coli or yeast optimized IGF-1 codons. None of these strain or plasmid modifications caused any significant increase in export of IGF-1 into the growth medium of JM101. Solubility studies of LamB-IGF-1 and processed IGF-1 showed that virtually all of the LamB-IGF-1 and IGF-1 remaining within the cell after a 2 h induction period was insoluble. This implied that only soluble LamB-IGF-1 was processed to IGF-1 and that only soluble IGF-1 was exported into the growth medium. Taken together, the results indicated that LamB-IGF-1 and IGF-1 solubility were the limiting factors in secretion of IGF-1 into the periplasm and export of IGF-1 into the growth medium.     

NCI-H716 cells as a model for endocrine differentiation in colorectal cancer

In colonic neoplasms, endocrine differentiation is encountered not only in carcinoid tumors but also in adenocarcinomas, where endocrine cells may represent a distinct line of differentiation in the tumor. The significance of endocrine differentiation in colorectal cancer is not well established, partly because of the paucity of tumor cell lines which can serve as a model for studying endocrine differentiation. In this report we describe the properties of NCI-H716 cells, a cell line derived from a poorly differentiated adenocarcinoma of the caecum, under various in vitro conditions and as xenografts in athymic mice. Phenotypical properties were immunohistochemically assessed using a panel of differentiation related antibodies, and also by Northern blot analysis and by electron microscopy. Receptors for biogenic amines and peptide hormones were analyzed by ligand binding assay. These studies show that:

Calcium is necessary for light excitation in barnacle photoreceptors

Summary Illumination of barnacle (Balanus amphitrite) photoreceptors is known to increase the membrane permeability to sodium and Ca²⁺ ions resulting in a depolarizing receptor potential. In this report, we show that lanthanum (La³⁺), a known inhibitor of Ca-binding proteins, reversibly eliminates the receptor potential of barnacle photoreceptors when applied to the extracellular space. Similar reversible elimination of the light response was obtained by removing extracellular Ca²⁺ by application of the calcium chelating agent EGTA. Iontophoretic injection of Ca²⁺, but not K⁺ into the cells protected both the transient and the steady-state phases of the receptor potential from elimination by EGTA while only the transient phase was protected in the presence of La³⁺. The EGTA experiments suggest that internal Ca²⁺ is necessary for light excitation of barnacle photoreceptors while the La³⁺ experiments suggest that La³⁺-sensitive inward current is necessary to maintain excitation during prolonged light.Abbreviations EGTA ethylenglyol-bis-(-aminoethylether) N, N, N¹, N¹-tetraacetate - BAPTA bis-(0-aminophenoxy)-ethane-N, N, N¹, N¹-tetraacetic acid - DMSO dimethyl sulfoxide - trp transient receptor potential - nss no steady state - ASW artificial sea water