University of Extremadura

About: University of Extremadura is a education organization based out in Badajoz, Spain. It is known for research contribution in the topics: Population & Hyperspectral imaging. The organization has 7856 authors who have published 18299 publications receiving 396126 citations. The organization is also known as: Universidad de Extremadura.

Role of TGF beta s and BMPs as signals controlling the position of the digits and the areas of interdigital cell death in the developing chick limb autopod

Abstract: The establishment of the digital rays and the interdigital spaces in the developing limb autopod is accompanied by the occurrence of corresponding domains of expression of TGF beta s and BMPs. This study analyzes whether these coincident events are functionally correlated. The experiments consisted of local administration of TGF beta-1, TGF beta-2 or BMP-4 by means of heparin or Affi-gel blue beads to the chick limb autopod in the stages preceding the onset of interdigital cell death. When beads bearing either TGF beta-1 or -2 were implanted in the interdigits, the mesodermal cells were diverted from the death program forming ectopic cartilages or extra digits in a dose- and stage-dependent fashion. This change in the interdigital phenotype was preceded by a precocious ectopic expression of ck-erg gene around the bead accompanied by down-regulation of bmp-4, msx-1 and msx-2 gene expression. When BMP-beads were implanted in the interdigital spaces, programmed cell death and the freeing of the digits were both accelerated. Implantation of beads bearing BMP-4 at the tip of the growing digits was followed by digit bifurcation, accompanied by the formation of an ectopic area of cell death resembling an extra interdigit, both morphologically and molecularly. The death-inducing effect of the BMP beads and the chondrogenic-inducing effect of the TGF beta beads were antagonized by the implantation of an additional bead preabsorbed with FGF-2, which constitutes a signal characteristic of the progress zone. It is concluded that the spatial distribution of digital rays and interdigital spaces might be controlled by a patterned distribution of TGF beta s and BMPs in the mesoderm subjacent to the progress zone.

Spectral–Spatial Classification of Hyperspectral Data Using Loopy Belief Propagation and Active Learning

Abstract: In this paper, we propose a new framework for spectral-spatial classification of hyperspectral image data. The proposed approach serves as an engine in the context of which active learning algorithms can exploit both spatial and spectral information simultaneously. An important contribution of our paper is the fact that we exploit the marginal probability distribution which uses the whole information in the hyperspectral data. We learn such distributions from both the spectral and spatial information contained in the original hyperspectral data using loopy belief propagation. The adopted probabilistic model is a discriminative random field in which the association potential is a multinomial logistic regression classifier and the interaction potential is a Markov random field multilevel logistic prior. Our experimental results with hyperspectral data sets collected using the National Aeronautics and Space Administration's Airborne Visible Infrared Imaging Spectrometer and the Reflective Optics System Imaging Spectrometer system indicate that the proposed framework provides state-of-the-art performance when compared to other similar developments.

Auxin regulates aquaporin function to facilitate lateral root emergence

Abstract: Aquaporins are membrane channels that facilitate water movement across cell membranes. In plants, aquaporins contribute to water relations. Here, we establish a new link between aquaporin-dependent tissue hydraulics and auxin-regulated root development in Arabidopsis thaliana. We report that most aquaporin genes are repressed during lateral root formation and by exogenous auxin treatment. Auxin reduces root hydraulic conductivity both at the cell and whole-organ levels. The highly expressed aquaporin PIP2;1 is progressively excluded from the site of the auxin response maximum in lateral root primordia (LRP) whilst being maintained at their base and underlying vascular tissues. Modelling predicts that the positive and negative perturbations of PIP2;1 expression alter water flow into LRP, thereby slowing lateral root emergence (LRE). Consistent with this mechanism, pip2;1 mutants and PIP2;1-overexpressing lines exhibit delayed LRE. We conclude that auxin promotes LRE by regulating the spatial and temporal distribution of aquaporin-dependent root tissue water transport.

Targeted genomic disruption of H-ras and N-ras, individually or in combination, reveals the dispensability of both loci for mouse growth and development.

Abstract: In eukaryotes, Ras proteins are highly conserved from yeast to humans These proteins include several subfamilies (Rho, Rab, Ras, Ran) of small GTP-binding proteins acting as a biological switches for various cellular processes In mammals, the Ras subfamily includes three highly homologous H-, N-, and K-Ras proteins, as well as other structurally and functionally related proteins, such as Ral, Rap, R-Ras, and TC21 (14, 27, 29) Ras proteins are essential signaling intermediates in eukaryotic cells The Ras-signaling pathway begins with upstream activation at the cell surface via tyrosine kinase or cytokine receptors, or βγ subunits of heterotrimeric G proteins (8, 38) Subsequent formation of an active Ras-GTP complex triggers downstream signaling cascades resulting in modulation of DNA transcription at the cell nucleus (9, 16, 21, 27, 29, 32, 36) Although this pathway has been mostly depicted as a single, linear path linking the cell surface to nuclear responses, it is increasingly evident that Ras proteins are part of more versatile, branched signaling networks The mammalian H-, N-, and K-ras genes are expressed ubiquitously (7, 12, 26), raising questions about functional specificity or redundancy for each of these ras family members Studies of yeast and mice indicate that ras gene function is partially dispensable for normal development and cell survival Yeasts lacking one of their two ras genes are viable (20), while N-ras homozygous mutant mice grow normally (47) On the other hand, K-ras is essential for normal mouse development (18, 24) Homozygous K-ras−/− embryos die progressively between embryonic day 125 and term of gestation, with fetal liver defects and anemia (18) At day 115, there is increased cell death of motoneurons in the medulla and the cervical spinal chord, and at day 155 of gestation, ventricular walls are very thin (24) Additional evidence for unique roles of H-, K-, and N-ras are as follows: (i) many tumors are associated with mutations in one specific ras family member (3), and (ii) although it is ubiquitous, the levels of ras mRNA in mice appear to be regulated both temporally and spatially, with certain tissues expressing one or more members of the family preferentially (26) N-ras and K-ras are highly expressed during early development, but levels decrease around postnatal day 10, while H-ras is highly expressed throughout development, with abundant expression in the adult brain Furthermore, in the juvenile rat brain, H-ras is highly expressed in the neocortex, hippocampus, entorhinal cortex, striatum, thalamus, and cerebellum while the overall levels of expression of N- and K-ras are significantly lower (44, 49, 50) Due to the ubiquitous expression of the three ras genes in mammalian tissues, it is difficult to determine specificity, if any, of each of the ras gene products regarding tissue or function or activation by specific guanine nucleotide exchange factors Ras proteins and the neuronal Ras guanine nucleotide exchange factor Ras-GRF (also known as CDC25Mm) may play an important role in neurotransmission and plasticity in vivo (4, 6, 22) A recent in vitro report suggested that H-Ras alone is specifically activated by Ras-GRF (19), a finding consistent with the similar pattern of expression of H-ras and Ras-GRF observed in the rat brain (49) It has also been reported that H-ras, but not K-ras, traffics to the plasma membrane through the exocytic pathway (1) Gene targeting experiments have indicated that N-ras is dispensable for mouse development or survival and that K-ras plays an important role in embryogenesis (18, 24, 47) In the present study, we targeted the H-ras gene in mice to determine the role of this gene in embryonic and adult mouse development, with emphasis on its potential role in neuronal differentiation Furthermore, we also bred the H-ras knockout animals with previously available N-ras null mutant mice in order to ascertain the potential effects of the resultant double mutation in both ras loci

Continued Fraction Expansion Approaches to Discretizing Fractional Order Derivatives—an Expository Review

Abstract: This paper attempts to present an expository review of continued fraction expansion (CFE) based discretization schemes for fractional order differentiators defined in continuous time domain. The schemes reviewed are limited to infinite impulse response (IIR) type generating functions of first and second orders, although high-order IIR type generating functions are possible. For the first-order IIR case, the widely used Tustin operator and Al-Alaoui operator are considered. For the second order IIR case, the generating function is obtained by the stable inversion of the weighted sum of Simpson integration formula and the trapezoidal integration formula, which includes many previous discretization schemes as special cases. Numerical examples and sample codes are included for illustrations.