Molecular phylogeny of the Tylenchina and evolution of the female gonoduct (Nematoda: Rhabditida)

Tylenchina are a morphologically and functionally diverse group of nematode species that range from free-living bacteriovores, over transitory grazing root-hair feeders to highly specialized plant-parasites with complex host associations. We performed phylogenetic analyses of small subunit rDNA sequences from 97 species including an analysis that account for the RNA secondary structure in the models of evolution. The present study confirms the sister relationship of the bacteriovore Cephalobidae with the predominantly plant-parasitic Tylenchomorpha. All analyses appoint the fungal-feeding Aphelenchidae and Aphelenchoididae as being polyphyletic but the morphology based hypothesis of their monophyly could not be significantly rejected. Within the Tylenchomorpha, the families that exclusively parasitize higher plants are joined in a single clade. However, only the monophyletic position of the (super)families Hoplolaimidae and Criconematoidea were supported; Anguinidae, Tylenchidae, Belonolaimidae and Pratylenchidae appeared to be paraphyletic or polyphyletic. Parsimony and likelihood ancestral state reconstruction revealed that burrowing endoparasitism and sedentary endoparasitism each evolved, respectively, at least six and at least three times independently, mostly from migratory ectoparasitic ancestors. Only root-knot nematodes have evolved from burrowing endoparasitic nematodes. Traditional classifications are partially misled by this convergent evolution of feeding type and associated morphology. Contrastingly, mapping attributes of the gonoduct cellular architecture, including newly obtained data of 18 species belonging to the Aphelenchoidea, Criconematoidea, Anguinidae and Panagrolaimidae, revealed a broad congruence of the gonoduct characters and the molecular phylogenetic hypothesis. Yet, the presence of an offset spermatheca and proliferation of uterus cells has evolved multiple times, the latter associated with derived endoparasitic feeding specialization and resulting reproduction mode. Ancestral state reconstruction further revealed that the gonoduct of the morphologically and ecologically dissimilar tylenchid and cephalobid nematodes evolved from a common ancestor.     

Constraint and developmental dissociation of phenotypic integration in a genetically accommodated trait

SUMMARY The genetic accommodation of novel adaptive traits may be accompanied by the evolution of correlated traits that constrain adaptive evolution. Very little is known about the removal of maladaptive correlated traits. In the present study, body size was found to have evolved as a correlated trait during the artificial selection for a polyphenism and a monophenism, and the developmental basis underlying this correlated trait was investigated. The body size and coloration were found to be developmentally integrated by titers of the insect developmental hormone, juvenile hormone (JH). Attempts to uncouple the two traits resulted in the evolution of one of the body size determinants—the critical weight—but not the delay period whose evolution is constrained by JH titers. Thus, maladaptive correlated traits can be removed when multiple developmental modules exist, and the evolution of one or more of these modules is not constrained.     

Size matters (but so does time), and it's OK to be different

In this issue of Developmental Cell, Layalle et al. reveal new insights into how nutrition controls body size in Drosophila. Nutrition specifically affects the activity of target of rapamycin (TOR) in the prothoracic gland. Under low-nutrition conditions, TOR suppresses ecdysone secretion--which otherwise terminates larval development--thereby prolonging growth and allowing larvae to still attain a near-normal body size.     

Down-regulation of pyrophosphate: fructose 6-phosphate 1-phosphotransferase (PFP) activity in sugarcane enhances sucrose accumulation in immature internodes

Pyrophosphate: fructose 6-phosphate 1-phosphotransferase (PFP) activity was successfully down-regulated in sugarcane using constitutively expressed antisense and untranslatable forms of the sugarcane PFP-β gene. In young internodal tissue activity was reduced by up to 70% while no residual activity could be detected in mature tissues. The transgenic plants showed no visible phenotype or significant differences in growth and development under greenhouse and field conditions. Sucrose concentrations were significantly increased in the immature internodes of the transgenic plants but not in the mature internodes. This contributed to an increase in the purity of the immature tissues, resembling an early ripening phenotype. Both the immature and mature internodes of the transgenic plants had significantly higher fibre contents. These findings suggest that PFP influences the ability of young, biosynthetically active sugarcane culm tissue to accumulate sucrose but that the equilibrium of the glycolytic intermediates, including the stored sucrose, is restored when ATP-dependent phosphofructokinase and the residual PFP activity is sufficient to sustain the required glycolytic flux as the tissue matures. Moreover, it suggests a role for PFP in glycolytic carbon flow, which could be rate limiting under conditions of high metabolic activity.     

Evaluation of novel hyphodermin derivatives as glycogen phosphorylase a inhibitors

The lipophilicity, permeability, solubility, polar surface area and 'rule-of-five' properties were assessed, using QikProp v2.5 (Schr?dinger, Inc.) and ALOGPS 2.1 calculations, for 25 Hyphodermin derivatives. These compounds obeyed the 'rule-of-five', and the calculated physicochemical values were generally within desired limits. All compounds were tested against Glycogen Phosphorylase a (GPa). Four phenyl and benzyl substituted 2-oxo-hexahydro and tetrahydrobenzo[cd]indole carboxylic acids were identified as novel inhibitors of GPa with estimated IC(50) values in the range 0.8-1.3mM. Molecular modelling of these novel inhibitors was used to obtain the main structural features of this class of molecule for future structure-activity relationship studies.     

Telomere length assessment: biomarker of chronic oxidative stress?

Telomeres are nucleoprotein structures, located at the ends of chromosomes and are subject to shortening at each cycle of cell division. They prevent chromosomal ends from being recognized as double strand breaks and protect them from end to end fusion and degradation. Telomeres consist of stretches of repetitive DNA with a high G-C content and are reported to be highly sensitive to damage induced by oxidative stress. The resulting DNA strand breaks can be formed either directly or as an intermediate step during the repair of oxidative bases. In contrast to the majority of genomic DNA, there is evidence that telomeric DNA is deficient in the repair of single strand breaks. Since chronic oxidative stress plays a major role in the pathophysiology of several chronic inflammatory diseases, it is hypothesized that telomere length is reducing at a faster rate during oxidative stress. Therefore, assessment of telomere length might be a useful biomarker of disease progression. In this review several features of telomere length regulation, their relation with oxidative stress, and the potential application of measurement of telomere length as biomarker of chronic oxidative stress, will be discussed.     

N-Isotope effects on the Raman spectra of Fe2S2 ferredoxin and Rieske ferredoxin: evidence for structural rigidity of metal sites

The diiron ferredoxins have a common diamond-core structure with two bridging sulfides, but differ in the nature of their terminal ligands: either four cysteine thiolates in the Fe(2)S(2) ferredoxins or two cysteine thiolates and two histidine imidazoles in the Rieske ferredoxins. Contributions of the bridging (b) and terminal (t) ligands to the resonance Raman spectra of the Fe(2)S(2) ferredoxins have been distinguished previously by isotopic substitution of the bridging sulfides. We now find that uniform (15)N-labeling of Anabaena Fe(2)S(2) ferredoxin results in shifts of -1 cm(-1) in the Fe-S(t) stretching modes at 282, 340, and 357 cm(-1). The (15)N dependence is ascribed to kinematic coupling of the Fe-S(Cys) stretch with deformations of the cysteine backbone, including the amide nitrogen. No (15)N dependence occurs for the nu(Fe-S(b)) modes at 395 and 426 cm(-1). Similar effects are observed for the Rieske center in T4MOC ferredoxin from the toluene-4-monooxygenase system of Pseudomonas mendocina. Upon selective (15)N-labeling of the alpha-amino group of cysteine, the vibrational modes at 321, 332, 350, and 362 cm(-1) all undergo shifts of -1 to -2 cm(-1), thereby identifying them as combinations of nu(Fe-S(t)) and delta(Cys). These same four modes undergo similar isotope shifts when T4MOC ferredoxin is selectively labeled with (15)N-histidine ((15)N in either the alpha1,delta1 or delta1,epsilon2 positions). Thus, the Fe-S(Cys) stretch must also be undergoing kinematic coupling with vibrations of the Fe-His moiety. The extensive kinematic coupling of iron ligand vibrations observed in both the Fe(2)S(2) and Rieske ferredoxins presumably arises from the rigidity of the protein framework and is reminiscent of the behavior of cupredoxins. In both cases, the structural rigidity is likely to play a role in minimizing the reorganization energy for electron transfer.     

Scaling aspects of lymphocyte trafficking

We consider the long lived pool of B and T cells that recirculate through blood, tissues and the lymphatic system of an animal with body mass M. We derive scaling rules (allometric relations) for: (1) the rate of production of mature lymphocytes, (2) the accumulation of lymphocytes in the tissues, (3) the flux of lymphocytes through the lymphatic system, (4) the number of lymph nodes, (5) the number of lymphocytes per clone within a lymph node, and (6) the total number of lymphocytes within a lymph node. Mass-dependent aspects of immune learning and of the immunological self are shown to be not very significant. Our treatment is somewhat heuristic and aims at combining immunological data with recent progress in biological scaling.