Promises and limits of an agency perspective in evolutionary developmental biology

An agent-based perspective in the study of complex systems is well established in diverse disciplines, yet is only beginning to be applied to evolutionary developmental biology. In this essay, we begin by defining agency and associated terminology formally. We then explore the assumptions and predictions of an agency perspective, apply these to select processes and key concept areas relevant to practitioners of evolutionary developmental biology, and consider the potential epistemic roles that an agency perspective might play in evo devo. Throughout, we discuss evidence supportive of agential dynamics in biological systems relevant to evo devo and explore where agency thinking may enrich the explanatory reach of research efforts in evolutionary developmental biology.     

Methylarginine efflux in nutrient-deprived yeast mitigates disruption of nitric oxide synthesis

Amino Acids - Protein arginine N-methyltransferases (PRMTs) have emerged as important actors in the eukaryotic stress response with implications in human disease, aging, and cell signaling....     

Direct resolution of enantiomers of basic imidazol-2-yl-substituted alcohols by gas chromatography on chirasil-val

The direct resolution of enantiomers of a series of imidazol-2-yl-substituted alcohols has been achieved by gas chromatography on a well-deactivated fused-silica capillary column, coated with L -Chirasil-Val as the chiral stationary phase. The separation of these basic compounds is accomplished without exaggerated peak tailing. Compared to simpler alcohols the resolution factors (α) observed are extraordinarily large. While the imidazolyl substituent may contribute to the mechanism of the chiral discrimination, the crucial interaction is assumed to be through the hydroxy group, based on the observation that the resolution factors for the corresponding O-acetyl derivatives are markedly reduced. © 1993 Wiley-Liss, Inc.     

Influence of nitrate supply on concentrations and translocation of abscisic acid in barley (Hordeum vulgare)

Spring barley ( Hordeum vulgare L. cv. Golf) was grown at different nitrate supply rates, controlled by using the relative addition rate technique, in order to elucidate the relationship between nitrate-N supply and root and shoot levels of abscisic acid (ABA). The plants were maintained as (1) standard cultures where nitrate was supplied at relative addition rates (RAs) of 0.03, 0.09 and 0.18 day⁻¹, and (2) split-root cultures at RA 0.09 day⁻¹ but with the nitrate distributed between the two root parts in ratios of 100:0, 80:20 and 60:40. Time-dependent changes in root and shoot concentrations of ABA (determined by radioimmunoassay using a monoclonal antibody) were observed in both standard and split-root cultures during 12 days of acclimation to the different nitrate regimes. However, the ABA responses were similar at all nitrate supply rates. Further experiments were performed with split-root cultures where the distribution of nitrate between the two root parts was reversed from 80:20 to 20:80 so that short-term effects to local perturbations of nitrate supply could be studied without altering whole-plant N absorption. Transient increases in ABA concentrations (maximum of 25 to 40% after 3 to 4 h) were observed in both subroot parts, as well as in xylem sap and shoot tissue. By pruning the root system it was demonstrated that the change in ABA had its origin in the subroot part receiving the increased nitrate supply (i.e. switched from 20 to 80% of the total nitrate supply). The data indicate that ABA responses are easily transmitted between different organs, including transmission from one set of seminal roots to another via the shoot. The data do not provide any indication that long-term nitrate supplies or general nitrogen status of barley plants affect, or are otherwise related to, the average tissue ABA concentrations of roots and shoots.     

Extracellular polysaccharide of Nostoc commune (Cyanobacteria) inhibits fusion of membrane vesicles during desiccation

Cells of the cyanobacterium Nostoc commune secrete a complex, high molecular weight, extracellular polysaccharide (EPS) which accumulates to more than 60% of the dry weight of colonies. The EPS was purified from the clonal isolate N. commune DRH1. The midpoint of the membrane phase transition (T_m) of desiccated cells of N. commune CHEN was low (T_{m dry} = 8 °C) and was comparable to the T_m of rehydrated cells((T_m)_H20 = 6 °C). The EPS was not responsible for the depression of T_m. However, the EPS, at low concentrations, inhibited specifically the fusion of phosphatidylcholine membrane vesicles when they were dried in vitro at0% relative humidity (−400 MPa). Low concentrations of a trehalose:sucrose mixture, in a molar ratio which corresponded with that present in cells in vivo, together with small amounts of the EPS, were efficient in preventing leakage of carboxyfloroscein (CF) from membrane vesicles. Freeze-fracture electron microscopy resolved complex changes in the structure of the EPS and the outer membrane in response to rehydration of desiccated cells. The capacity of the EPS to prevent membrane fusion, the maintenance of a low T_{m dry} in desiccated cells, and the changes in rheological properties of the EPS in response to water availability, constitute what are likely important mechanisms for desiccation tolerance in this cyanobacterium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Protein kinase C is regulated in vivo by three functionally distinct phosphorylations

Background: Protein kinase Cs are a family of enzymes that transduce the plethora of signals promoting lipid hydrolysis. Here, we show that protein kinase C must first be processed by three distinct phosphorylations before it is competent to respond to second messengers.Results We have identified the positions and functions of the in vivo phosphorylation sites of protein kinase C by mass spectrometry and peptide sequencing of native and phosphatase-treated kinase from the detergent-soluble fraction of cells. Specifically, the threonine at position 500 (T500) on the activation loop, and T641 and S660 on the carboxyl terminus of protein kinase C βII are phosphorylated in vivo. T500 and S660 are selectively dephosphorylated in vitro by protein phosphatase 2A to yield an enzyme that is still capable of lipid-dependent activation, whereas all three residues are dephosphorylated by protein phosphatase 1 to yield an inactive enzyme. Biochemical analysis reveals that protein kinase C autophosphorylates on S660, that autophosphorylation on S660 follows T641 autophosphorylation, that autophosphorylation on S660 is accompanied by the release of protein kinase C into the cytosol, and that T500 is not an autophosphorylation site.Conclusion Structural and biochemical analyses of native and phosphatase-treated protein kinase C indicate that protein kinase C is processed by three phosphorylations. Firstly, trans-phosphorylation on the activation loop (T500) renders it catalytically competent to autophosphorylate. Secondly, a subsequent autophosphorylation on the carboxyl terminus (T641) maintains catalytic competence. Thirdly, a second autophosphorylation on the carboxyl terminus (S660) regulates the enzyme's subcellular localization. The conservation of each of these residues (or an acidic residue) in conventional, novel and atypical protein kinase Cs underscores the essential role for each in regulating the protein kinase C family.     

Ganglioside biosynthesis. Characterization of CMP-N-acetylneuraminic acid : lactosylceramide sialyltransferase in Golgi apparatus from rat liver.

An enzyme that transfers sialic acid from GMP-sialic acid to lactosylceramide was concentrated 40-50 times in Golgi apparatus from rat liver relative to total homogenates. This enzyme required detergents as dispersing agents. Of the numerous detergents tested, the combination Tween 80-Triton CF-54 (1 : 2, w/w) was the most effective in stimulating the reaction. Two apparent pH optima, at 6.35 and 5.5, were observed. The enzyme showed no requirement for a divalent cation. The Km values calculated for CMP-N-acetylneuraminic acid and lactosylceramide were 2.7 - 10(-3) and 1.3 - 10(-4) M, respectively. The enzyme could not be dissociated from Golgi apparatus fractions by treatment with ultrasound, indicating that it is tightly associated with the membrane. The newly synthesized GM3, the product of the reaction, was incorporated into or became tightly associated with the membranes of the Golgi apparatus.     

Neuronal repair and avoidance behavior in the flatworm,Notoplana acticola

In Notoplana avoidance behavior is lost after bisection of the brain or removal of one of its lobes. Behavioral recovery usually occurs within 3–10 days. Recovery of individuals may be gradual or abrupt. Grouped data shows gradual linear repair of turning behavior. Most animals with all connectives between the two lobes of the brain severed recovered preoperative responses, while those with one lobe of the brain removed averaged about 60% of the preoperative level of response. Some individuals in both groups recovered completely. Histological evidence of neuronal repair was found in all animals. Where the lobes of the brain were separated, connectives between them appeared to re-form. In worms with one lobe of the brain removed, the nerves disconnected by the excision joined the remaining lobe. Action potentials are conducted across repaired tissue in both split-brain and half-brain worms in both seawater and Mg²⁺-rich solutions. CNS repair appears to involve functional synaptic contacts. Notoplana does not replace ganglionic tissue but does compensate adequately for CNS damage.     

Specific localization of 2′,3′-cyclic nucleotide 3′-phosphohydrolase, (Ca/Mg)-ATPase, and acetylcholinesterase in human erythyrocyte membrane

A procedure was developed for the detection of 2′,3′-cyclic nucleotide 3′-phosphohydrolase in myelin. This assay was sufficiently sensitive to detect the low levels of 2′,3′-cyclic nucleotide 3′-phosphohydrolase in human erythrocytes. The 2′,3′-cyclic nucleotide 3′-phosphohydrolase of human erythrocytes was determined to be exclusively associated with the inner (cytosolic) side of the membrane. Leaky ghostsand resealed ghosts were assayed for 2′,3′-cyclic nucleotide 3′-phosphohydrolase, (Ca²⁺/Mg²⁺-ATPase, and acetylcholinesterase activity, and the 2′,3′-cyclic nucleotide 3′-phosphohydrolase profile is the same as that of the (Ca²⁺/Mg²⁺)-ATPase, an established inner membrane maker.