Determinaciòn espectrofotométrica de metami trona en lixiviados de suelo mediante regresión por mínimos cuadrados parciales

Se desarrolló un método sencillo y selectivo para la determinación espectrofotométrica del herbicida metamitrona en presencia de materia orgánica e hierro, cuyas interferencias fueron eliminadas mediante la Regresión por Mínimos Cuadrados Parciales Tipo I. El modelo de calibración se construyó a partir de una serie de 21 muestras, con concentraciones que oscilaron en el intervalo de 0 a 15 g mL-1 de metamitrona, de 0 a 400 g mL-1 de la sal sódica de ácidos húmicos y de 0 a 50 g mL-1 de sulfato férrico. Para una serie de 15 muestras de validación se estimó un porcentaje de recuperación de 95 ± 6 %, con un error estándar de predicción de 0.6, utilizando un intervalo espectral de 251 a 350 nm, datos centrados sobre la media y dos factores, para la construcción del modelo de calibración.Finalmente, se obtuvo un porcentaje de recuperación de 90 ± 11 % en el análisis de lixiviados acuosos fortificados con metamitrona, provenientes de un suelo franco arcilloso, con un contenido de carbono orgánico del 17 %.

The actin-myosin regulatory MRCK kinases: regulation, biological functions and associations with human cancer

The contractile actin-myosin cytoskeleton provides much of the force required for numerous cellular activities such as motility, adhesion, cytokinesis and changes in morphology. Key elements that respond to various signal pathways are the myosin II regulatory light chains (MLC), which participate in actin-myosin contraction by modulating the ATPase activity and consequent contractile force generation mediated by myosin heavy chain heads. Considerable effort has focussed on the role of MLC kinases, and yet the contributions of the myotonic dystrophy-related Cdc42-binding kinases (MRCK) proteins in MLC phosphorylation and cytoskeleton regulation have not been well characterized. In contrast to the closely related ROCK1 and ROCK2 kinases that are regulated by the RhoA and RhoC GTPases, there is relatively little information about the CDC42-regulated MRCKα, MRCKβ and MRCKγ members of the AGC (PKA, PKG and PKC) kinase family. As well as differences in upstream activation pathways, MRCK and ROCK kinases apparently differ in the way that they spatially regulate MLC phosphorylation, which ultimately affects their influence on the organization and dynamics of the actin-myosin cytoskeleton. In this review, we will summarize the MRCK protein structures, expression patterns, small molecule inhibitors, biological functions and associations with human diseases such as cancer

Studying the present, understanding the past

Actuopaleontology is an essential discipline to understand the fossil record. It uses the present as a key to understand the past. Actualistic paleontology has been largely used in a vast array of paleontological fields such as ichnology, paleoart or functional morphology. Given its relevance in current and past paleontological studies, here we examine the advantages of this discipline, focusing in four recent works. In them, the study of contemporary groups allows us to know better if it is possible: to know how reliable is amber when studying extinct arthropods communities; to make trophic inferences about extinct elasmobranchs by dental microwear analysis; to reconstruct the morphology of certain fishes depending on its ecological niche or to find the type of flight in extinct birds considering their humerus morphology

Myosin II isoforms play distinct roles in adherens junction biogenesis

International audienceAdherens junction (AJ) assembly under force is essential for many biological processes like epithelial monolayer bending, collective cell migration, cell extrusion and wound healing. The acto-myosin cytoskeleton acts as a major force-generator during the de novo formation and remodeling of AJ. Here, we investigated the role of non-muscle myosin II isoforms (NMIIA and NMIIB) in epithelial junction assembly. NMIIA and NMIIB differentially regulate biogenesis of AJ through association with distinct actin networks. Analysis of junction dynamics, actin organization, and mechanical forces of control and knockdown cells for myosins revealed that NMIIA provides the mechanical tugging force necessary for cell-cell junction reinforcement and maintenance. NMIIB is involved in E-cadherin clustering, maintenance of a branched actin layer connecting E-cadherin complexes and perijunctional actin fibres leading to the building-up of anisotropic stress. These data reveal unanticipated complementary functions of NMIIA and NMIIB in the biogenesis and integrity of AJ

Structure and tree diversity of secondary dry tropical forests in the Sierra de Huautla Biosphere Reserve, Morelos

"Se estudió la recuperación en riqueza, composición, estructura y diversidad arbórea en 3 condiciones de bosque tropical caducifolio secundario con diferente tiempo de abandono (C35, C45 y C65 años) en el sureste del estado de Morelos. En cada condición se establecieron 3 unidades de muestreo de 50 × 50 m (2,500 m2) y se midieron a todos los individuos ≥ 2.5 cm de diámetro normal (DN). En total se registraron 2,791 individuos, pertenecientes a 79 especies, 53 géneros y 30 familias. Fabaceae fue la familia con el mayor número de especies e individuos. C45 presentó la mayor riqueza de especies (57), seguida de C35 (48) y C65 (43). Las condiciones fueron diferentes (p < 0.0001) en área basal, altura total, DN y cobertura de copa. Las especies con mayores índices relativos de valor de importancia (IVIR) y de valor forestal (IVFR) fueron Pachycereus grandis (IVIR = 22.6, IVFR = 28.7), Amphipterygium adstringens (IVIR = 20.9, IVFR = 17.0), Lysiloma divaricatum (IVIR = 11.2, IVFR = 18.9) y Quercus glaucoides (IVIR = 10.5, IVFR = 13.1). Se encontraron diferencias altamente significativas (p < 0.001) entre condiciones de abandono para la heterogeneidad (Shannon-Wiener: H´), y valores significativamente (p < 0.05) mayores en C65 para el recíproco de Simpson (1/D), así como en C35 y C45 para los índices de Margalef (DMG) y α de Fisher (S). La semejanza florística (Sorensen: Is) fue máxima entre condiciones con menor tiempo de abandono (72%) y mínima con la condición de mayor tiempo (54%). El procedimiento de permutación de respuesta múltiple indicó diferencias significativas (p < 0.05) en la composición de especies entre condiciones tempranas (C35 y C45) y tardías (C65). Estos resultados explican el proceso de la sucesión secundaria en los bosques tropicales caducifolios del área de estudio y dan elementos para efectuar una mejor planificación de las actividades conducentes a su conservación.""The recovery in richness, composition, structure and tree diversity was studied in three conditions of secondary tropical deciduous forest with different time of abandonment (C35, C45 and C65 years) in the southeast of the state of Morelos. In each condition, three plots of 50 × 50 m (2,500 m2) were established and all individuals ≥ 2.5 cm of normal diameter (ND) were measured. In total, 2,791 individuals belonging to 79 species, 53 genera and 30 families were registered. Fabaceae was the family with the largest number of species and individuals. C45 had the highest species richness (57), followed by C35 (48) and C65 (43). The conditions were different (p < 0.0001) in basal area, total height, ND and crown coverage. The species with the highest relative value of importance (IVIR) and forest value (IVFR) were Pachycereus grandis (IVIR = 22.6, IVFR = 28.7), Amphipterygium adstringens (IVIR = 20.9, IVFR = 17.0), Lysiloma divaricatum (IVIR =11.2, IVFR = 18.9) and Quercus glaucoides (IVIR = 10.5, IVFR = 13.1). High significant differences (p < 0.001) between abandonment conditions were found for heterogeneity (Shannon-Wiener: H’), and highest significant values (p < 0.05) for Simpson reciprocal index (1/D) in C65, as well as to Margalef (DMG) and Fisher’s α (S) indexes in C35 and C45. The floristic similarity (Sorensen: Is) was highest among conditions with less time of abandonment (72%) and minimum with the condition of greater time (54%). The multiple response permutation procedure indicated significant differences (p < 0.05) in the species composition between early (C35 and C45) and late (C65) conditions. These results explain the process of secondary succession in the tropical deciduous forests of the study area and provide elements for improve planning of the activities leading to its conservation.

β-Adrenergic Inhibition of Contractility in L6 Skeletal Muscle Cells

The β-adrenoceptors (β-ARs) control many cellular processes. Here, we show that β-ARs inhibit calcium depletion-induced cell contractility and subsequent cell detachment of L6 skeletal muscle cells. The mechanism underlying the cell detachment inhibition was studied by using a quantitative cell detachment assay. We demonstrate that cell detachment induced by depletion of extracellular calcium is due to myosin- and ROCK-dependent contractility. The β-AR inhibition of L6 skeletal muscle cell detachment was shown to be mediated by the β2-AR and increased cAMP but was surprisingly not dependent on the classical downstream effectors PKA or Epac, nor was it dependent on PKG, PI3K or PKC. However, inhibition of potassium channels blocks the β2-AR mediated effects. Furthermore, activation of potassium channels fully mimicked the results of β2-AR activation. In conclusion, we present a novel finding that β2-AR signaling inhibits contractility and thus cell detachment in L6 skeletal muscle cells by a cAMP and potassium channel dependent mechanism

A novel Rac-dependent checkpoint in B cell development controls entry into the splenic white pulp and cell survival

Rac1 and Rac2 GTPases transduce signals from multiple receptors leading to cell migration, adhesion, proliferation, and survival. In the absence of Rac1 and Rac2, B cell development is arrested at an IgD− transitional B cell stage that we term transitional type 0 (T0). We show that T0 cells cannot enter the white pulp of the spleen until they mature into the T1 and T2 stages, and that this entry into the white pulp requires integrin and chemokine receptor signaling and is required for cell survival. In the absence of Rac1 and Rac2, transitional B cells are unable to migrate in response to chemokines and cannot enter the splenic white pulp. We propose that loss of Rac1 and Rac2 causes arrest at the T0 stage at least in part because transitional B cells need to migrate into the white pulp to receive survival signals. Finally, we show that in the absence of Syk, a kinase that transduces B cell antigen receptor signals required for positive selection, development is arrested at the same T0 stage, with transitional B cells excluded from the white pulp. Thus, these studies identify a novel developmental checkpoint that coincides with B cell positive selection

The Na+/H+ exchanger NHE1 is required for directional migration stimulated via PDGFR-α in the primary cilium

We previously demonstrated that the primary cilium coordinates platelet-derived growth factor (PDGF) receptor (PDGFR) α–mediated migration in growth-arrested fibroblasts. In this study, we investigate the functional relationship between ciliary PDGFR-α and the Na+/H+ exchanger NHE1 in directional cell migration. NHE1 messenger RNA and protein levels are up-regulated in NIH3T3 cells and mouse embryonic fibroblasts (MEFs) during growth arrest, which is concomitant with cilium formation. NHE1 up-regulation is unaffected in Tg737orpk MEFs, which have no or very short primary cilia. In growth-arrested NIH3T3 cells, NHE1 is activated by the specific PDGFR-α ligand PDGF-AA. In wound-healing assays on growth-arrested NIH3T3 cells and wild-type MEFs, NHE1 inhibition by 5′-(N-ethyl-N-isopropyl) amiloride potently reduces PDGF-AA–mediated directional migration. These effects are strongly attenuated in interphase NIH3T3 cells, which are devoid of primary cilia, and in Tg737orpk MEFs. PDGF-AA failed to stimulate migration in NHE1-null fibroblasts. In conclusion, stimulation of directional migration in response to ciliary PDGFR-α signals is specifically dependent on NHE1 activity, indicating that NHE1 activation is a critical event in the physiological response to PDGFR-α stimulation

Theoretical Model for Cellular Shapes Driven by Protrusive and Adhesive Forces

The forces that arise from the actin cytoskeleton play a crucial role in determining the cell shape. These include protrusive forces due to actin polymerization and adhesion to the external matrix. We present here a theoretical model for the cellular shapes resulting from the feedback between the membrane shape and the forces acting on the membrane, mediated by curvature-sensitive membrane complexes of a convex shape. In previous theoretical studies we have investigated the regimes of linear instability where spontaneous formation of cellular protrusions is initiated. Here we calculate the evolution of a two dimensional cell contour beyond the linear regime and determine the final steady-state shapes arising within the model. We find that shapes driven by adhesion or by actin polymerization (lamellipodia) have very different morphologies, as observed in cells. Furthermore, we find that as the strength of the protrusive forces diminish, the system approaches a stabilization of a periodic pattern of protrusions. This result can provide an explanation for a number of puzzling experimental observations regarding cellular shape dependence on the properties of the extra-cellular matrix