Thermodynamic and kinetic destabilization of triosephosphate isomerase resulting from the mutation of conserved and non-conserved cysteines

Several variants of Saccharomyces cerevisiae triosephosphate isomerase (yTIM) were studied to determine how mutations of conserved and non-conserved Cys residues affect the enzyme. Wild-type yTIM has two buried free cysteines: Cys 41 (non-conserved) and the invariant Cys 126. Single-site mutants, containing substitutions of these cysteines with Ala, Val, or Ser (the three most conservative changes for a buried Cys, according to substitution matrices), were examined for stability and enzymatic activity. Neither of the Cys residues was found to be essential for enzyme catalysis. Determination of the global stability of the mutants indicated that, regardless of which Cys was substituted, individual Cys→Ala and Cys→Val mutations, as well as the C41S substitution, all decrease the unfolding free energy of the dimeric protein by less than 23 kJ mol(-1) (at 37 °C, pH 7.4), as compared to the wild-type enzyme. In contrast, a substantially larger destabilization (37 kJ mol(-1)) was found in the C126S mutant. These results suggest that, with the exception of C126S, all of these mutations can be regarded as neutral (i.e., mutations that do not impair the reproductive success of the organism). Accordingly, Cys 126 has remained invariant across evolution because its neutral substitutions by Ala or Val would require a highly unlikely, concerted double mutation at any of the Cys codons. Furthermore, detrimental effects to a cell expressing the C126S TIM mutant more likely arise from the high unfolding rate of this enzyme.     

Risk Perception and Chronic Exposure to Organochlorine Pesticides in Maya Communities of Mexico

In order to analyze risk perception related to the use and handling of organochlorine pesticides (OCP) in agricultural and livestock activities among Maya communities of Yucatan, Mexico, and to study their impact on public health and the environment, we conducted an analytical study applying 274 semi-structured interviews in 11 municipalities in the zone called “Ring of Cenotes.” The harmful effects of agrochemicals on water supplies, soils, air, and human health were considered, including the indoor use of pesticides to preserve harvest products. Recent studies showed high levels of OCP in groundwater. A generalized low risk perception related to human health and the environment due to pesticide use was found. Likewise, social parameters were analyzed, including the educational level, as well as risk factors related to groundwater karst vulnerability. Pesticides that have been banned by international conventions are still in use. The occurrence of some diseases such as cervical cancer, with a very high prevalence at the national level, and the practice of obtaining drinking water from polluted wells and sinkholes, may be associated with this low risk perception and with poor social conditions. Establishing programs on health education, agro-ecological production alternatives, and water chemical quality monitoring is recommended.     

A recipe for postfledging survival in great tits Parus major: be large and be early (but not too much)

Survival of juveniles during the postfledging period can be markedly low, which may have major consequences on avian population dynamics. Knowing which factors operating during the nesting phase affect postfledging survival is crucial to understand avian breeding strategies. We aimed to obtain a robust set of predictors of postfledging local survival using the great tit (Parus major) as a model species. We used mark–recapture models to analyze the effect of hatching date, temperatures experienced during the nestling period, fledging size and body mass on first‐year postfledging survival probability of great tit juveniles. We used data from 5192 nestlings of first clutches ringed between 1993 and 2010. Mean first‐year postfledging survival probability was 15.2%, and it was lower for smaller individuals, as well as for those born in either very early or late broods. Our results stress the importance of choosing an optimum hatching period, and raising large chicks to increase first‐year local survival probability in the studied population.     

Description of a new epibiotic relationship (Suctorian–Copepoda) in NE Atlantic waters: from morphological to phylogenetic analyses

Paraeuchaeta hebes is one of the most important carnivorous copepods in the coastal upwelling system off Galician waters (Ría de Vigo, NE Atlantic). A suctorian epibiont of the genus Pelagacineta was found attached to the surface of these copepods. The abundance and distribution on the copepod surface were analysed, taking into account the sex of the crustacean, revealing some preference for females and also a different attachment point in both sexes. The morphological study allowed us to identify a new species of this Suctoria epibiont as Pelagacineta hebensis. Moreover, the 18S rRNA gene was partially sequenced to inspect the phylogenetic position of Pelagacineta hebensis within the subclass Phyllopharyngea. The maximum‐likelihood (ML) tree obtained was consistent with the morphological and with previous molecular studies and showed that P. hebensis belongs to the order Endogenina, as a sister clade of the few taxa sequenced within this order. Including new genetic data to the Endogenina will allow building new hypothesis about the evolution of the most derived clade of suctorians.     

Antipredatory Response and Food Intake in Wood Mice (Apodemus sylvaticus) under Simulated Predation Risk by Resident and Novel Carnivorous Predators

Chemical signals left by predators are a potential source of information about the risk of predation, and small mammals are known to take them into account when making decisions. We investigated whether wood mice (Apodemus sylvaticus) are more likely to avoid the faeces of resident predators (red fox Vulpes vulpes and common genet Genetta genetta) vs. a novel predator (European pine marten Martes martes). Odour recognition would increase perceived predation risk and reduce food intake by individual mice. Wood mice response to predators was analysed by live‐trapping using two untreated controls (baited/non‐baited) and traps experimentally manipulated with three predator treatments (faeces of red fox, common genet or pine marten). Traps were baited with 4 g of toasted corn, and food intake by wood mice was determined as the amount of bait remaining in each trap. We found that traps treated with faeces of resident predators were the most avoided, and the number of captures in traps treated with pine marten faeces was similar to the control‐baited traps. The variation found in food intake was explained by the interaction between the types of treatment and breeding condition. Food intake was similar in control‐baited traps and in traps with faeces of pine marten, but when predation risk by resident predators (red fox and common genet) was simulated, breeders reduced food intake significantly as compared to non‐breeders. These results indicate that predator recognition and feeding behaviour under predation risk depend on individual factors and the balance of costs‐benefits in each particular predation risk situation at a given place and time.     

Regulation of the p19Arf/p53 pathway by histone acetylation underlies neural stem cell behavior in senescence‐prone SAMP8 mice

Brain aging is associated with increased neurodegeneration and reduced neurogenesis. B1/neural stem cells (B1‐NSCs) of the mouse subependymal zone (SEZ) support the ongoing production of olfactory bulb interneurons, but their neurogenic potential is progressively reduced as mice age. Although age‐related changes in B1‐NSCs may result from increased expression of tumor suppressor proteins, accumulation of DNA damage, metabolic alterations, and microenvironmental or systemic changes, the ultimate causes remain unclear. Senescence‐accelerated‐prone mice (SAMP8) relative to senescence‐accelerated‐resistant mice (SAMR1) exhibit signs of hastened senescence and can be used as a model for the study of aging. We have found that the B1‐NSC compartment is transiently expanded in young SAMP8 relative to SAMR1 mice, resulting in disturbed cytoarchitecture of the SEZ, B1‐NSC hyperproliferation, and higher yields of primary neurospheres. These unusual features are, however, accompanied by premature loss of B1‐NSCs. Moreover, SAMP8 neurospheres lack self‐renewal and enter p53‐dependent senescence after only two passages. Interestingly, in vitro senescence of SAMP8 cells could be prevented by inhibition of histone acetyltransferases and mimicked in SAMR1 cells by inhibition of histone deacetylases (HDAC). Our data indicate that expression of the tumor suppressor p19, but not of p16, is increased in SAMP8 neurospheres, as well as in SAMR1 neurospheres upon HDAC inhibition, and suggest that the SAMP8 phenotype may, at least in part, be due to changes in chromatin status. Interestingly, acute HDAC inhibition in vivo resulted in changes in the SEZ of SAMR1 mice that resembled those found in young SAMP8 mice.     

Nodal/Activin signaling drives self-renewal and tumorigenicity of pancreatic cancer stem cells and provides a target for combined drug therapy

Nodal and Activin belong to the TGF-β superfamily and are important regulators of embryonic stem cell fate. Here we investigated whether Nodal and Activin regulate self-renewal of pancreatic cancer stem cells. Nodal and Activin were hardly detectable in more differentiated pancreatic cancer cells, while cancer stem cells and stroma-derived pancreatic stellate cells markedly overexpressed Nodal and Activin, but not TGF-β. Knockdown or pharmacological inhibition of the Nodal/Activin receptor Alk4/7 in cancer stem cells virtually abrogated their self-renewal capacity and in vivo tumorigenicity, and reversed the resistance of orthotopically engrafted cancer stem cells to gemcitabine. However, engrafted primary human pancreatic cancer tissue with a substantial stroma showed no response due to limited drug delivery. The addition of a stroma-targeting hedgehog pathway inhibitor enhanced delivery of the Nodal/Activin inhibitor and translated into long-term, progression-free survival. Therefore, inhibition of the Alk4/7 pathway, if combined with hedgehog pathway inhibition and gemcitabine, provides a therapeutic strategy for targeting cancer stem cells.