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El sistema financiero se ha vuelto un tema de estudio de gran relevancia para las áreas económicas y financieras, las cuales buscan nuevos métodos para obtener una visión acertada en la toma de decisiones por parte de los diferentes inversionistas. Por ello, el presente documento tiene como propósito mostrar cómo la aplicación de la metodología de rango reescalado y exponente de Hurst logra analizar y determinar la persistencia y las estructuras con fenómenos irregulares (autocorrelación) dentro del mercado colombiano. Para ello, se tomaron como muestra cinco de las acciones más representativas de la bolsa de valores de Colombia y del índice Colcap (grupo Aval, Ecopetrol, Bancolombia y el grupo Éxito), así como sus rendimientos, de acuerdo con sus oscilaciones durante un periodo de cinco años. Al implementar la metodología de Rango Reescalado, se encontró que los activos analizados presentan fenómenos de persistencia y antipersistencia en las series de tiempo, lo que muestra que ninguna de las acciones se encuentra bajo el supuesto de normalidad. Por lo tanto, es necesario implementar nuevas herramientas que permitan mayor firmeza en los análisis, como pueden ser el R/S modificado, expuesto por Lo (1991) o variables que permitan determinar procesos estocásticos dentro de las series, lo cual es fundamental para brindar una mayor rigurosidad al cálculo matemático para que este apoye de una forma más eficiente a los inversionistas.

The aim of the present work is to describe for groups of age the different profiles of party identification, of political ideology and the grade of coherence between both. It was develop and apply a test on line that was answered by 1.776 subjects. The results shows that most of the subjects, independently of their age, identified with some political party (91.5 % of the sample). In older age groups, party identification's sign is more conservative (right) as against the more young cohorts with a more progressive sign (left and center-left). It's observed a general upward trend of the coherence between party identification and political ideology according to age, despite the inexistence of big differences between the different groups of age. Therefore, the results confirm the approaches of political socialization and their implications on the effects of life cycle in the political behavior. Adapted from the source document.

11 páginas, 8 figuras. ; The Snail gene family of transcription factors plays crucial roles in different morphogenetic processes during the development of vertebrate and invertebrate embryos. In previous studies of function interference for one of the family members, Slug, we showed its involvement and neural crest formation in the chick embryo. Now we have carried out a series of gain-of-function experiments in which we show that Slug overexpression in the neural tube of the chick embryo induces an increase in neural crest production. The analysis of electroporated embryos shows that Slug can induce the expression of rhoB and an increase in the number of HNK-1-positive migratory cells, indicating that it lies upstream of them in the genetic cascade of neural crest development. The increase in neural crest production after Slug overexpression was confined to the cranial region, indicating that the mechanisms of crest induction somehow differ between head and trunk. The expression of the two vertebrate family members, Slug and Snail, is peculiar with respect to the neural crest. Slug is not expressed in the premigratory crest in the mouse, whereas it is expressed in this cell population in the chick and the opposite is true for Snail ( Sefton, M., Sánchez, S. and Nieto M. A. (1998) Development , -3121 ). This raises the question of whether they can be functionally equivalent. To test this hypothesis both intra- and interspecies, we have performed a series of ectopic expression experiments by electroporating chick and mouse Snail in the chick embryo hindbrain. We observe that both genes elicit the same responses in the neural tube. Our results indicate that they can be functionally equivalent, although the embryos show a higher response to the endogenous gene, chick Slug. ; This work was supported by grants to M. A. N. from the Spanish Ministry of Culture (DGICYT-PM98-0125), the Comunidad Autónoma de Madrid (08.1/0044/2000) and the European Union (FMRX-CT96-0065) M. G. B. is the recipient of a predoctoral fellowship from the Comunidad Autónoma de Madrid. ; Peer reviewed

11 páginas, 10 figuras, 2 tablas. ; The members of the Snail family of zinc-finger transcription factors have been implicated in the formation of distinct tissues within the developing vertebrate and invertebrate embryo. Two members of this family have been described in higher vertebrates, Snail (Sna) and Slug (Slu), where they have been implicated in the formation of tissues such as the mesoderm and the neural crest. We have isolated the mouse homologue of the Slu gene enabling us to analyse and compare the amino acid sequences and the patterns of expression of both Sna and Slu in the chick and mouse. We have detected features in the sequences that allow the unequivocal ascription of any family member to the Sna or Slu subfamilies and we have observed that, during early stages of development, many of the sites of Slu and Sna expression in the mouse and chick embryo are swapped. Later in development, the sites of expression of Slu and Sna are conserved between these two species. These data, together with the data available in other species, lead us to propose that Slu and Sna arose as a duplication of an ancestor gene and that an extra duplication in the fish lineage has given rise to two Sna genes. Furthermore, several early sites of Slu and Sna expression have been swapped in the avian lineage. Our analysis of the Snail family may also shed new light on the origin of the neural crest. ; This work was supported by grants from the Spanish Ministry of Education and Culture (DGICYT-PM95-0024), the Comunidad Autónoma de Madrid (08.1/0020/97) and the European Union (FMRX-CT96-0065) to M. A. N.; M. S. was also the recipient of a Wellcome Trust Travel fellowship and S. S. is the recipient of a predoctoral fellowship from the Spanish Ministry of Education and Culture. ; Peer reviewed

Twelve commercially available edible marine algae from France, Japan and Spain and the certified reference material (CRM) NIES No. 9 Sargassum fulvellum were analyzed for total arsenic and arsenic species. Total arsenic concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after microwave digestion and ranged from 23 to 126 μg g−1. Arsenic species in alga samples were extracted with deionized water by microwave-assisted extraction and showed extraction efficiencies from 49 to 98%, in terms of total arsenic. The presence of eleven arsenic species was studied by high performance liquid chromatography–ultraviolet photo-oxidation–hydride generation atomic–fluorescence spectrometry (HPLC–(UV)–HG–AFS) developed methods, using both anion and cation exchange chromatography. Glycerol and phosphate sugars were found in all alga samples analyzed, at concentrations between 0.11 and 22 μg g−1, whereas sulfonate and sulfate sugars were only detected in three of them (0.6-7.2 μg g−1). Regarding arsenic toxic species, low concentration levels of dimethylarsinic acid (DMA) (<0.9 μg g−1) and generally high arsenate (As(V)) concentrations (up to 77 μg g−1) were found in most of the algae studied. The results obtained are of interest to highlight the need to perform speciation analysis and to introduce appropriate legislation to limit toxic arsenic species content in these food products.

10 páginas, 8 figuras. ; Eph receptors and their ligands, the ephrins, have been implicated in early patterning and axon guidance in vertebrate embryos. Members of these families play pivotal roles in the formation of topographic maps in the central nervous system, the formation of brain commissures, and in the guidance of neural crest cells and motor axons through the anterior half of the somites. Here, we report a highly dynamic expression pattern of the chick EphA7 gene in the developing limb. Expression is detected in discrete domains of the dorsal mesenchyme from 3 days of incubation. The expressing cells are adjacent to the routes where axons grow to innervate the limb at several key points: the region of plexus formation, the bifurcation between dorsal and ventral fascicles, and the pathway followed by axons innervating the dorsal muscle mass. These results suggested a role for EphA7 in cell-cell contact-mediated signalling in dorsal limb patterning and/or axon guidance. We carried out experimental manipulations in the chick embryo wing bud to alter the dorsoventral patterning of the limb. The analyses of EphA7 expression and innervation in the operated wings indicate that a signal emanating from the dorsal ectoderm regulates EphA7 in such a way that, in its absence, the wing bud lacks EphA7 expression and shows innervation defects at the regions where the gene was downregulated. EphA7 downregulation in the dorsal mesenchyme after dorsal ectoderm removal is more rapid than that of Lmx-1, the gene known to mediate dorsalisation in response to the ectodermal signal. These results add a new gene to the dorsalisation signalling pathway in the limb. Moreover, they implicate the Eph receptor family in the patterning and innervation of the developing limb, extending its role in axon pathfinding to the distal periphery. ; This work was supported by grants from the Spanish Ministry of Education and Culture (DGICYT-PM95-0024) and the European Union Biotech Programme (BIO4-CT96-0659) to M. A. N., and DGICYT-PM95-0088 to M. A. R.; M. A. and M. E. P. were the recipients of predoctoral fellowships (PFPI) from the Spanish Ministry of Education and Culture and M. T. H. of an ICI fellowship. ; Peer reviewed

8 páginas, 7 figuras, 1 tabla. ; Down-regulation ofE-cadherin expression is a determinant of tumor cell invasiveness, an event frequently associated with epithelial-mesenchymal transitions. Here we show that the mouse E12/E47 basic helix-loop-helix transcription factor (the E2A gene product) acts as a repressor of E-cadherin expression and triggers epithelial-mesenchymal transitions. The mouse E47 factor was isolated in a one-hybrid system designed to isolate repressors of the mouse E-cadherin promoter. Epithelial cells ectopically expressing E47 adopt a fibroblastic phenotype and acquire tumorigenic and migratory/invasive properties, concomitant with the suppression of E-cadherin expression. Suppression ofE-cadherin expression under stable or inducible expression of E47 in epithelial cells occurs at the transcriptional level and is dependent on the E-boxes of the E-cadherinpromoter. Interestingly, analysis of endogenous E2Aexpression in murine and human cell lines illustrated its presence in E-cadherin-deficient, invasive carcinoma cells but its absence from epithelial cell lines. This expression pattern is consistent with that observed in early mouse embryos, where E2A mRNA is absent from epithelia but strongly expressed in the mesoderm. These results implicate E12/E47 as a repressor of E-cadherinexpression during both development and tumor progression and indicate its involvement in the acquisition and/or maintenance of the mesenchymal phenotype. ; This work was supported by Spanish Ministry of Education and Culture Grants SAF98-0085-C03-01 (to A. C.), DGICYT-PM98-0125 (to M. A. N.), and PB97-0054 (to F. P.), Comunidad Autónoma de Madrid Grants 08.1/0024.1/99 and 08.1/0055./2000 (to A. C. and F. P.), and European Union Grant FMXR-CT96-0065 (to M. A. N.). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. ; Peer reviewed

The majority of animals show external bilateral symmetry, precluding the observation of multiple internal left-right (L/R) asymmetries that are fundamental for organ packaging and function1,2. In vertebrates, left identity is mediated by the left-specific Nodal-Pitx2 axis that is repressed on the right-hand side by the epithelial-mesenchymal transition (EMT) inducer Snail13,4. Despite some existing evidence3,5, it remains unclear whether an equivalent instructive pathway provides right-hand specific information to the embryo. Here we show that in zebrafish, BMP mediates the L/R asymmetric activation of another EMT inducer, Prrx1a, in the lateral plate mesoderm (LPM) with higher levels on the right. Prrx1a drives L/R differential cell movements towards the midline leading to a leftward displacement of the cardiac posterior pole through an actomyosin-dependent mechanism. Downregulation of Prrx1a prevents heart looping and leads to mesocardia. Two parallel and mutually repressed pathways, respectively driven by Nodal and BMP on the left and right LPM, converge on the asymmetric activation of Pitx2 and Prrx1, two transcription factors that integrate left and right information to govern heart morphogenesis. This mechanism is conserved in the chicken embryo and, in the mouse, Snail1 fulfills the role played by Prrx1 in fish and chick. Thus, a differential L/R EMT produces asymmetric cell movements and forces, more prominent from the right, that drive heart laterality in vertebrates.

9 páginas, 7 figuras. ; The Snail genes are implicated in processes that involve cell movement, both during embryonic development and tumour progression. In teleosts, the vertebrate Snail1 gene is represented by two distinct genes, snail1a and snail1b (previously snail1 and snail2). These genes are expressed in complementary mesodermal domains and their combined expression matches that of their mammalian counterpart. By analysing their loss and gain of function, we found that the most-anterior axial mesendodermal cells, the precursors of the polster, move in a cohesive manner directed by the activity of snail1a- and snail1b-expressing cells surrounding these precursors. The cell-autonomous function of Snail1 proteins regulates cell motility and influences the behaviour of Snail-negative neighbouring cells. Snail1a is required by the prechordal plate for it to reach its normal position, whereas Snail1b controls the acquisition of its normal shape. These non-redundant functions of Snail1a and Snail1b in controlling axial mesendoderm migration comply with the duplication-degeneration-complementation model, and indicate that Snail genes not only act as inducers of epithelial-to-mesenchymal transition, but also as more general regulators of cell adhesion and movement. ; This work was supported by grants of the Spanish Ministry of Education and Science (DGICYT-BMC2002-0383; MECBFU2004- 02665 and MEC-BFU2005-05772) and the regional Government of Valencia (GV04B-292) to M.A.N.; GV05-028 to A.B.G. and Fondecyt 1031003, ICM P02-050, ICGEB CRP/CHI03-03 to M.L.A. M.J.B. and A.B.-G. hold Ramon y Cajal Contracts (Spanish Ministry of Education and Science) and H.A. is contracted under the I3P Programme (European Social Fund/CSIC). ; Peer reviewed