Population genetics of Agave cocui: evidence for low genetic diversity at the southern geographic limit of genus Agave

The Agave genus embraces many species with outstanding ecological and economic importance in the arid regions of the Americas. Even though this genus covers a broad geographic distribution, our knowledge on the population genetics of species is concentrated in taxa located in North America. Recently, it has been demonstrated that plant domestication decreases levels of genetic diversity in managed populations and increases population structure with respect to wild populations. We examined levels of allozyme diversity (N = 17 loci) and population structure of Agave cocui, the species at the southern limit of distribution of the genus. We sampled 7 wild populations (N = 30-35 individuals per population) representative of the geographic distribution of the species in Venezuela. Among the agaves studied, A. cocui has some of the lowest estimates of genetic diversity (H(e)[species] = 0.059, H(e)[population] = 0.054) reported until present. We propose that this condition is probably linked to the recent origin of this species in arid and semiarid regions of Colombia and Venezuela, probably through one or a few founder events. The lowest estimates of genetic diversity were associated with small populations in very restricted arid patches; but also with overexploitation of rosettes for production of fermented drinks and fibers. Santa Cruz de Pecaya, one of the 2 centers of economic use of agaves in northwestern Venezuela presented one of the lowest values of genetic variability, a sign suggesting that human impact represents a significant threat to the available genetic pool that this species possesses in the region.     

A polymorphism in <Emphasis Type="Italic">PTPN2</Emphasis> gene is associated with an earlier onset of type 1 diabetes

The Wellcome Trust Case Control Consortium (WTCCC) genome-wide study found association of PTPN2 with three autoimmune diseases, among them is type 1 diabetes (T1D). This result was confirmed by a follow-up study that pointed to new independent signals within the region. However, both studies were performed in patients with an early-onset T1D. We aimed at replicating the previous results and studying the influence of these polymorphisms in the age at T1D debut. We genotyped 439 T1D Spanish subjects (age at onset, 1 to 65 years) and 861 controls for two PTPN2 single nucleotide polymorphisms (SNPs), rs2542151 and rs478582, and studied the effect of both polymorphisms in age at onset through stratified and continuous analyses. The frequency of rs2542151*G carriers was significantly higher in the early-onset group compared with late-onset patients (p = 0.023) and with controls (OR = 1.61 [1.14–2.26]; p = 0.005). No significant differences were found between controls and late-onset patients. The log-rank chi-square test for the Kaplan–Meier plots (carriers of susceptibility allele vs non carriers) was statistically significant (χ _1df² = 4.485; p = 0.034), yielding an earlier disease debut for G carriers. The analysis of the SNP rs478582 did not reach statistical significance. In summary, we replicate the association detected by the WTCCC and propose that the rs2542151*G allele confers risk to an earlier onset of T1D.     

Epilithic biofilms provide large amounts of nitrogen to tropical mountain landscapes

We show that epilithic biofilms are a relevant nitrogen (N) source in a rocky mountain range in Brazil. During different seasons, we quantified nitrate, ammonium, dissolved organic N (DON) and total dissolved N (TDN) leached by a simulated short rain event. We quantified the epilithic autotrophic biomass by taxonomic groups and its correlation with leached N. We hypothesized that leached N would be correlated to heterocystous cyanobacteria biomass since they are more efficient N₂ fixers. We estimated a landscape N supply of 8.5 kg.ha⁻¹.year⁻¹ considering the mean precipitation in the region. TDN in leachate was mainly composed of DON (83.8% ± 22%), followed by nitrate (12.1% ± 3%) and ammonium (5% ± 5%). The autotrophic epilithic community was mainly composed of non-heterocystous (Gloeocapsopsis) and heterocystous cyanobacteria (Scytonema and Stigonema), except for a site more commonly affected by fire events that showed a dominance of Chlorophyta. Biogeochemical upscaling was facilitated by the fact that N leaching was not different among sites or related to autotrophic epilithic biomass or assemblage composition. In conclusion, the capacity of epilithic biofilms to provide N to surrounding systems is an ecosystem service that underscores the necessity to conserve them and their habitats.     

The K-factor,Covitality, and personality

We present a psychometric test of life history theory as applied to human individual differences using MIDUS survey data (Brim et al. 2000). Twenty scales measuring cognitive and behavioral dimensions theoretically related to life history strategy were constructed using items from the MIDUS survey. These scales were used to construct a single common factor, the K-factor, which accounted for 70% of the reliable variance. The scales used included measures of personal, familial, and social function. A second common factor, Covitality, was constructed from scales for physical and mental health. Finally, a single general factor, Personality, was constructed from scales for the “Big Five” factors of personality. The K-factor, covitality factor, and general personality factor correlated significantly with each other, supporting the prediction that high K predicts high somatic effort and also manifests in behavioral display. Thus, a single higher-order common factor, the Super-K factor, was constructed that consisted of the K-factor, covitality factor, and personality factor.     

Genetic and eco-physiological differences of South American Cylindrospermopsis raciborskii isolates support the hypothesis of multiple ecotypes

The global distribution of the toxic cyanobacterium Cylindrospermopsis raciborskii has recently increased, and it has now been identified in tropical, subtropical and temperate freshwater bodies. The mechanisms underlying its success and expansion are still unknown. Several hypotheses have been proposed, including climate change, natural selection and physiological tolerance to different environmental conditions. In this study, we determined the phenotypic and genotypic characteristics of two recently isolated South American strains of C. raciborskii obtained from Uruguay. We analyzed the morphology, growth preferences, tolerance to low temperature (14 °C) and toxin production of the strains and performed phylogenetic analyses based on the ITS and nifH gene sequences. Both isolates showed significantly different morphology and growth behavior under different light intensities and phosphate supply. When genetic differences were assessed by BOX PCR, cluster analyses revealed that they could also be distinguished genotypically and were clearly distinct from C. raciborskii isolated from other continents. Phylogenetic analysis showed that the Uruguayan strains were closely affiliated to other C. raciborskii isolated from the Americas, especially to those from Brazil. Similar to previous studies, we found three solid clusters (Africa-Australia, Europe and America) according to the geographical origin of the isolates. Interestingly, based on nifH sequences, subclusters were identified in American populations indicating an early spread of the species within the continent. We propose that phenotypic and genetic variability of C. raciborskii populations is linked to the existence of different ecotypes whose success is subject to the local environmental conditions.     

The α-defensin salt-bridge induces backbone stability to facilitate folding and confer proteolytic resistance

Salt-bridge interactions between acidic and basic amino acids contribute to the structural stability of proteins and to protein–protein interactions. A conserved salt-bridge is a canonical feature of the α-defensin antimicrobial peptide family, but the role of this common structural element has not been fully elucidated. We have investigated mouse Paneth cell α-defensin cryptdin-4 (Crp4) and peptide variants with mutations at Arg⁷ or Glu¹⁵ residue positions to disrupt the salt-bridge and assess the consequences on Crp4 structure, function, and stability. NMR analyses showed that both (R7G)-Crp4 and (E15G)-Crp4 adopt native-like structures, evidence of fold plasticity that allows peptides to reshuffle side chains and stabilize the structure in the absence of the salt-bridge. In contrast, introduction of a large hydrophobic side chain at position 15, as in (E15L)-Crp4 cannot be accommodated in the context of the Crp4 primary structure. Regardless of which side of the salt-bridge was mutated, salt-bridge variants retained bactericidal peptide activity with differential microbicidal effects against certain bacterial cell targets, confirming that the salt-bridge does not determine bactericidal activity per se. The increased structural flexibility induced by salt-bridge disruption enhanced peptide sensitivity to proteolysis. Although sensitivity to proteolysis by MMP7 was unaffected by most Arg⁷ and Glu¹⁵ substitutions, every salt-bridge variant was degraded extensively by trypsin. Moreover, the salt-bridge facilitates adoption of the characteristic α-defensin fold as shown by the impaired in vitro refolding of (E15D)-proCrp4, the most conservative salt-bridge disrupting replacement. In Crp4, therefore, the canonical α-defensin salt-bridge facilitates adoption of the characteristic α-defensin fold, which decreases structural flexibility and confers resistance to degradation by proteinases.     

The heritability of life history strategy: the K-factor, covitality, and personality

Archival data from the MIDUS survey (Brim et al., 2000), a nationally representative sample, on 309 MZ and 333 DZ twin pairs aged 25-74 years were used to test the psychometrics and behavioral genetics of life history strategy. We organized 253 of the originally administered 2,000 questions into 30 scales measuring life history traits (e.g., quality of family relationships and altruism towards kin), medical symptoms (e.g., thyroid problems), personality traits (e.g., neuroticism, extraversion, conscientiousness), and social background (e.g., financial security). A single higher-order factor, indicating a general life history strategy, composed of three lower-order factors, was replicated. Factor analyses were then performed on the genetic variance-covariance matrices. We found that (a) a single higher-order factor explained the preponderance of the genetic correlations among the scales and (b) this higher-order factor was itself 68 percent heritable and accounted for 82 percent of the genetic variance among the three component lower-order factors.     

Preconditioning limits mitochondrial Ca(2+) during ischemia in rat hearts: role of K(ATP) channels

Prolonged myocardial ischemia results in an increase in intracellular calcium concentration ([Ca(2+)]i), which is thought to play a critical role in ischemia-reperfusion injury. Ischemic preconditioning (PC) improves myocardial function during ischemia-reperfusion, a process that may involve opening mitochondrial ATP-sensitive potassium (K(ATP)) channels. Because pharmacological limitation of mitochondrial calcium concentration ([Ca(2+)]m) overload during ischemia-reperfusion has been shown to improve myocardial function, we hypothesized that PC would reduce [Ca(2+)]m during ischemia-reperfusion and that this effect was mediated by opening mitochondrial K(ATP) channels. Isolated rat hearts were subjected to 25 min of global ischemia and 30 min of reperfusion with or without PC in the presence of mitochondrial K(ATP) channel opening (diazoxide, 100 microM) and blockade [5-hydroxydecanoic acid (5-HD), 100 microM]. Contracture during ischemia (end-diastolic pressure) and functional recovery on reperfusion (developed pressure) were assessed. Total [Ca(2+)]i and [Ca(2+)]m were measured using indo 1 fluorescence. Both PC and diazoxide limited the increase in end-diastolic pressure and resulted in greater functional recovery after 30 min of reperfusion, functional effects that were partially or completely abolished by 5-HD. PC and diazoxide also significantly limited the increase in [Ca(2+)]m during ischemia-reperfusion. In addition, PC lowered [Ca(2+)]i during reperfusion, whereas diazoxide paradoxically resulted in increased [Ca(2+)]i during reperfusion. There was an inverse linear relationship between [Ca(2+)]m and developed pressure during reperfusion. PC limits the ischemia-induced increase in mitochondrial, but not total, [Ca(2+)]i, an effect mediated by opening mitochondrial K(ATP) channels. These data suggest that the lowering of mitochondrial calcium overload is a mechanism of cardioprotection in PC.