Transferrin's mechanism of interaction with receptor 1

The kinetics and thermodynamics of the interactions of transferrin receptor 1 with holotransferrin and apotransferrin in neutral and mildly acidic media are investigated at 37 degrees C in the presence of CHAPS micelles. Receptor 1 interacts with CHAPS in a very fast kinetic step (<1 micros). This is followed in neutral media by the interaction with holotransferrin which occurs in two steps after receptor deprotonation, with a proton dissociation constant (K(1a)) of 10.0 +/- 1.5 nM. The first step is detected by the T-jump technique and is associated with a molecular interaction between the receptor and holotransferrin. It occurs with a first-order rate constant (k(-1)) of (1.6 +/- 0.2) x 10(4) s(-1), a second-order rate constant (k(1)) of (3.20 +/- 0.2) x 10(10) M(-1) s(-1), and a dissociation constant (K(1)) of 0.50 +/- 0.07 microM. This step is followed by a slow change in the conformation with a relaxation time (tau(2)) of 3400 +/- 400 s and an equilibrium constant (K(2)) of (4.6 +/- 1.0) x 10(-3) with an overall affinity of the receptor for holotransferrin [(K'1)(-1)] of (4.35 +/- 0.60) x 10(8) M(-1). Apotransferrin does not interact with receptor 1 in neutral media, between pH 4.9 and 6, it interacts with the receptor in two steps after a receptor deprotonation (K(2a) = 2.30 +/- 0.3 microM). The first step occurs in the range of 1000-3000 s. It is ascribed to a slow change in the conformation which rate-controls a fast interaction between apotransferrin and receptor 1 with an overall affinity constant [(K(3))(-1)] of (2.80 +/- 0.30) x 10(7) M(-1). These results imply that receptor 1 probably exists in at least two forms, the neutral species which interacts with holotransferrin and not with apotransferrin and the acidic species which interacts with apotransferrin. At first, the interaction of the neutral receptor with holotransferrin is extremely fast. It is followed by the slow change in conformation, which leads to an important stabilization of the thermodynamic structure. In the acidic media of the endosome, the interaction of apotransferrin with the acidic receptor is sufficiently strong and rate-controlled by a very slow change in conformation which allows recycling back to the plasma membrane.     

Spermiogenesis and ultrastructure of the spermatozoon of the liver fluke Fasciola gigantica Cobbold, 1856 (Digenea: Fasciolidae), a parasite of cattle in Senegal

The present paper describes the spermiogenesis and the ultrastructure of the spermatozoon of Fasciola gigantica, as revealed by transmission electron microscopy. Spermiogenesis in F. gigantica begins with the formation of a differentiation zone containing 2 centrioles with associated striated roots and an intercentriolar body between them. Each centriole develops a flagellum. Proximodistal fusion of these flagella with the median cytoplasmic extension gives rise to the spermatozoon. Spermiogenesis in F. gigantica is characterized by the formation of a dorsolateral cytoplasmic expansion, an external ornamentation of the cell membrane, and spinelike bodies. These 3 structures were also observed in the anterior part of the spermatozoon. Our study describes for the first time the simultaneous presence of dorsolateral cytoplasmic expansion, external ornamentation of the plasma membrane, and spinelike bodies in the spermatozoon of a trematode.     

Phenotypic evolution of human craniofacial morphology after admixture: a geometric morphometrics approach

An evolutionary, diachronic approach to the phenotypic craniofacial pattern arisen in a human population after high levels of admixture and gene flow was achieved by means of geometric morphometrics. Admixture has long been studied after molecular data. Nevertheless, few efforts have been made to explain the morphological outcome in human craniofacial samples. The Spanish-Amerindian contact can be considered a good scenario for such an analysis. Here we present a comparative analysis of craniofacial shape changes observed between two putative ancestor groups, Spanish and precontact Aztecs, and two diachronic admixed groups, corresponding to early and late colonial periods from the Mexico's Central Valley. Quantitative shape comparisons of Amerindian, Spanish, and admixed groups were used to test the expectations of quantitative genetics for admixture events. In its simplest form, this prediction states that an admixed group will present phenotypic values falling between those of both parental groups. Results show that, in general terms, although the human skull is a complex, integrated structure, the craniofacial morphology observed fits the theoretical expectations of quantitative genetics. Thus, it is predictive of population structure and history. In fact, results obtained after the craniofacial analysis are in accordance with previous molecular and historical interpretations, providing evidence that admixture is a main microevolutionary agent influencing modern Mexican gene pool. However, expectations are not straightforward when moderate shape changes are considered. Deviations detected at localized structures, such as the upper and lower face, highlight the evolution of a craniofacial pattern exclusively inherent to the admixed groups, indicating that quantitative characters might respond to admixture in a complicated, nondirectional way.     

Phylogenetic characterization and in situ detection of bacterial communities associated with seahorses (Hippocampus guttulatus) in captivity

Although there are several studies describing bacteria associated with marine fish, the bacterial composition associated with seahorses has not been extensively investigated since these studies have been restricted to the identification of bacterial pathogens. In this study, the phylogenetic affiliation of seahorse-associated bacteria was assessed by 16S rRNA gene sequencing of cloned DNA fragments. Fluorescence in situ hybridization (FISH) was used to confirm the presence of the predominant groups indicated by 16S rRNA analysis. Both methods revealed that Vibrionaceae was the dominant population in Artemia sp. (live prey) and intestinal content of the seahorses, while Rhodobacteraceae was dominant in water samples from the aquaculture system and cutaneous mucus of the seahorses. To our knowledge, this is the first time that bacterial communities associated with healthy seahorses in captivity have been described.     

New Aminoacyl-tRNA Synthetase-like Protein in Insecta with an Essential Mitochondrial Function

Aminoacyl-tRNA synthetases (ARS) are modular enzymes that aminoacylate transfer RNAs (tRNA) for their use by the ribosome during protein synthesis. ARS are essential and universal components of the genetic code that were almost completely established before the appearance of the last common ancestor of all living species. This long evolutionary history explains the growing number of functions being discovered for ARS, and for ARS homologues, beyond their canonical role in gene translation. Here we present a previously uncharacterized paralogue of seryl-tRNA synthetase named SLIMP (seryl-tRNA synthetase-like insect mitochondrial protein). SLIMP is the result of a duplication of a mitochondrial seryl-tRNA synthetase (SRS) gene that took place in early metazoans and was fixed in Insecta. Here we show that SLIMP is localized in the mitochondria, where it carries out an essential function that is unrelated to the aminoacylation of tRNA. The knockdown of SLIMP by RNA interference (RNAi) causes a decrease in respiration capacity and an increase in mitochondrial mass in the form of aberrant mitochondria.     

Interaction between head and neck squamous cell carcinoma cells and fibroblasts in the biosynthesis of PGE2

Prostaglandin (PG)E(2) is relevant in tumor biology, and interactions between tumor and stroma cells dramatically influence tumor progression. We tested the hypothesis that cross-talk between head and neck squamous cell carcinoma (HNSCC) cells and fibroblasts could substantially enhance PGE(2) biosynthesis. We observed an enhanced production of PGE(2) in cocultures of HNSCC cell lines and fibroblasts, which was consistent with an upregulation of COX-2 and microsomal PGE-synthase-1 (mPGES-1) in fibroblasts. In cultured endothelial cells, medium from fibroblasts treated with tumor cell-conditioned medium induced in vitro angiogenesis, and in tumor cell induced migration and proliferation, these effects were sensitive to PGs inhibition. Proteomic analysis shows that tumor cells released IL-1, and tumor cell-induced COX-2 and mPGES-1 were suppressed by the IL-1-receptor antagonist. IL-1α levels were higher than those of IL-1β in the tumor cell-conditioning medium and in the secretion from samples obtained from 20 patients with HNSCC. Fractionation of tumor cell-conditioning media indicated that tumor cells secreted mature and unprocessed forms of IL-1. Our results support the concept that tumor-associated fibroblasts are a relevant source of PGE(2) in the tumor mass. Because mPGES-1 seems to be essential for a substantial biosynthesis of PGE(2), these findings also strengthen the concept that mPGES-1 may be \a target for therapeutic intervention in patients with HNSCC.     

The effect of strobilurins on leaf gas exchange, water use efficiency and ABA content in grapevine under field conditions

Strobilurins are one of the most important classes of agricultural fungicides. In addition to their anti-fungal effect, strobilurins have been reported to produce simultaneous effects in plant physiology. This study investigated whether the use of strobilurin fungicide improved water use efficiency in leaves of grapevines grown under field conditions in a Mediterranean climate in southern Spain. Fungicide was applied three times in the vineyard and measurements of leaf gas exchange, plant water status, abscisic acid concentration in sap ([ABA]), and carbon isotope composition in leaves were performed before and after applications. No clear effect on stomatal conductance, leaf water potential and intrinsic water use efficiency was found after three fungicide applications. ABA concentration was observed to increase after fungicide application on the first day, vanishing three days later. Despite this transient effect, evolution of [ABA] matched well with the evolution of leaf carbon isotope ratio, which can be used as a surrogate for plant water use efficiency. Morning stomatal conductance was negatively correlated to [ABA]. Yield was enhanced in strobilurin treated plants, whereas fruit quality remained unaltered.     

Wnt signaling in planarians: new answers to old questions

Wnts are secreted glycoproteins involved in a broad range of essential cell functions, including proliferation, migration and cell-fate determination. Recent years have seen substantial research effort invested in elucidating the role of the Wnt signaling pathway in planarians, flatworms with incredible regenerative capacities. In this review, we summarize current knowledge on the role of canonical (β-catenin-dependent) and non-canonical (β-catenin-independent) Wnt signaling in planarians, not only during regeneration, but also during normal homeostasis. We also describe some of the preliminary data that has been obtained regarding the role of these pathways during embryogenesis. Models are proposed to integrate the different results which have been obtained to date and highlight those questions that still remain to be answered.     

Oxidative Stress Parameters in Urine from Patients with Disorders of Propionate Metabolism: a Beneficial Effect of l-Carnitine Supplementation

Propionic (PA) and methylmalonic (MMA) acidurias are inherited disorders caused by deficiency of propionyl-CoA carboxylase and methylmalonyl-CoA mutase, respectively. Affected patients present acute metabolic crises in the neonatal period and long-term neurological deficits. Treatments of these diseases include a protein restricted diet and l-carnitine supplementation. l-Carnitine is widely used in the therapy of these diseases to prevent secondary l-carnitine deficiency and promote detoxification, and several recent in vitro and in vivo studies have reported antioxidant and antiperoxidative effects of this compound. In this study, we evaluated the oxidative stress parameters, isoprostane and di-tyrosine levels, and the antioxidant capacity, in urine from patients with PA and MMA at the diagnosis, and during treatment with l-carnitine and protein-restricted diet. We verified a significant increase of isoprostanes and di-tyrosine, as well as a significant reduction of the antioxidant capacity in urine from these patients at diagnosis, as compared to controls. Furthermore, treated patients presented a marked reduction of isoprostanes and di-tyrosine levels in relation to untreated patients. In addition, patients with higher levels of protein and lipid oxidative damage, determined by di-tyrosine and isoprostanes levels, also presented lower urinary concentrations of total and free l-carnitine. In conclusion, the present results indicate that treatment with low protein diet and l-carnitine significantly reduces urinary biomarkers of protein and lipid oxidative damage in patients with disorders of propionate metabolism and that l-carnitine supplementation may be specially involved in this protection.     

A role for tRNA modifications in genome structure and codon usage

Transfer RNA (tRNA) gene content is a differentiating feature of genomes that contributes to the efficiency of the translational apparatus, but the principles shaping tRNA gene copy number and codon composition are poorly understood. Here, we report that the emergence of two specific tRNA modifications shaped the structure and composition of all extant genomes. Through the analysis of more than 500 genomes, we identify two kingdom-specific tRNA modifications as major contributors that separated archaeal, bacterial, and eukaryal genomes in terms of their tRNA gene composition. We show that, contrary to prior observations, genomic codon usage and tRNA gene frequencies correlate in all kingdoms if these two modifications are taken into account and that presence or absence of these modifications explains patterns of gene expression observed in previous studies. Finally, we experimentally demonstrate that human gene expression levels correlate well with genomic codon composition if these identified modifications are considered.