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Expression of Tgf-beta in the regenerative process of crinoid echinoderms
No full textFor many years, we focused our studies on the remarkable power of regeneration exhibited by crinoid echinoderms. Current investigations are exploring the aspects related to the 'putative' growth factors crucial for the regenerative process in crinoids. Due to its importance in wound healing phenomena of vertebrates and invertebrates, both in the embryo and in adults, the present study concentrates on the possible presence/expression and roles of TGF-β in arm regeneration processe of the crinoid Antedon mediterranea. This problem has been explored by employing 1) a biochemical and immunocytochemical approach, which allowed us to detect the presence of TGF-β1 and its putative changes of pattern distribution during the regeneration process; 2) a molecular approach, thanks to which we cloned a BMP2/4 homologue from crinoids (AnBMP2/4) confirming the possible presence of different genes of the TGF-β superfamily. Expression studies indicate an important role for AnBMP2/4 during the more advanced stages of regeneration at a time when new tissues are being established and the brachial nerve is extending into the regenerate. This expression in an ‘adult’ regenerating system shows remarkable parallels with recent investigations in sea urchin embryos where a BMP2/4 homologue is involved in the regulation of the ectoderm/endoderm boundary and epidermal/non epidermal fate decisions.
Our results suggest in particular that AnBMP2/4 plays an important role in crinoid skeletogenesis as well as in neurogenesis and support the idea of an evolutionary developmental programme where essential gene families are conserved throughout phylogeny both in terms of expression and function. The future employment of techniques such as RNA interference or bead implantation, in adult echinoderms, will be of fundamental importance to understand the function of AnBMP2/4 and other related genes
Stress and regeneration in crinoids and asteroids
No full textComplete and functional regrowth of arms in echinoderms depends on several factors. Probably the most crucial are the site of amputation along the proximal-distal axis of the arm, particularly important in crinoids (Candia Carnevali et al 1995), and the ambient temperature, as seen in the ophiuroid A. filiformis (Mallefet et al 2000). Indeed, a traumatic amputation that does not follow the natural autotomy plane may involve more complex reparative/regenerative mechanisms and therefore may be slower compared to the non traumatic (Candia Carnevali et al 1995). Whatever the selected regenerative ‘pathway’, massive tissue rearrangement and strong up-regulation of cell proliferation/differentiation was detected in all the species investigated in this thesis. However, the time course of these events does vary dependent upon the regenerative ‘pathways’.
During the arm regeneration process, these animals might experience stress which may be accompanied by a large turnover of protein. Generally, when an organism is subject to metabolic and environmental stressors, a common protective mechanism, known as the stress response, is activated (Srinivas and Swamynathan 1996; Morimoto 1998). This results in the expression of heat-shock proteins (Hsps). It is known that Hsps, which are encoded by highly conserved families of genes, play key roles not only in the correct folding of proteins (and hence repair processes following damage) but also during normal development (Becker and Craig 1994). One specific example occurs in Drosophila where small increases in Hsp70 expression during development enhances thermotolerance (Feder 1999) but if overexpression of the Hsp70 gene is induced, larval mortality increases and development slows down (Krebs and Feder 1997).
Amongst invertebrates, echinoderms are well known for their extensive capacity for regeneration following natural predation-induced trauma or as a part of reproductive strategy (Candia Carnevali et al 1998). Echinoderm classes with arms are often subject to frequent arm loss. Clearly such autotomy followed by subsequent repair and regeneration is likely to represent a stressful event.
Ubiquitin is a small, (76 amino acids) highly conserved phylogenetically, protein and is present in all eukaryotes (Finley and Chau, 1991; Hochstrasser, 1996). Although ubiquitin occurs free in the cell, it is most commonly found covalently conjugated to a wide range of target proteins. This conjugation is a reversible post-translational modification, which has been implicated, in numerous biological processes. Ubiquitin plays important roles in a range of cellular functions including the cell cycle, DNA replication, DNA repair and signal transduction (Deshaise 1995; Muller and Schwartz 1995; King et al 1996). One important and well-known function of ubiquitination is to target proteins for rapid degradation by the 26S proteasome, a protease complex present in both the cytoplasm and the nucleus (Arrigo et al 1988). In this ATP-dependent pathway, a protein is tagged with poly-ubiquitin chains via isopeptide bonds, which are formed between the carboxyl terminal glycine of ubiquitin molecules and the ε-amino groups of lysine residues in other ubiquitin molecules. This ubiquitinating reaction (Fig. 1) is catalysed by sequential actions of E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and often E3 (ubiquitin-ligase). When cells are exposed to heat shock, many aberrant proteins are produced and the ubiquitin-dependent proteolytic pathway (the ubiquitin-proteasome system) is believed to play a key role in rapid degradation of these abnormal proteins (Schwartz and Ciechanover 1999).
In contrast, some proteins, such as the histones H2A and H2B, are ubiquitinated but not subsequently degraded. It is still unclear whether these ubiquitin molecules are attached to histones via the poly-ubiquitin chain or not. Thus, it is still uncertain why and how ubiquitinated histones are deubiquitinated in response to heat-shock, during chromosome condensation in the mitotic cell cycle, in apoptosis and during neuronal differentiation in PC12h cells (Bond et al 1988; Takada et al 1994; Marushige and Marushige 1995)
PCB-induced environmental stress and the regenerative response in crinoids.
No full textSome persistent and ubiquitous pollutants (PCBs) which can affect the natural environment because of their bio-accumulation in organisms exert their effects by acting as “endocrine disrupters”. In this respect they interact with members of the nuclear receptor family and can induce dramatic effects on gene expression, reproductive competence and development. This paper focuses on the impact of such compounds on natural arm regeneration in crinoids. Since crinoids are benthic and microfilter-feeding animals they are particularly susceptible to the presence of micropollutants in marine sediments. We used the regenerative response of crinoids to monitor and evaluate chronic toxicity by means of tests performed in the laboratory under controlled conditions of known environmental parameters and contamination levels. Exposure to Aroclor 1260, a commercial cocktail of chlorinated congeners, have been performed in static conditions. The concentration of the pollutant has been analysed in both the water and in the whole animal during and at the end of tests. Since the phenomena of tissue renewal involves substantial cell cycle activity and proliferation, the crinoids regeneration bio-test represents an ideal bioindicator of stress at the cellular and molecular level due to persistent pollutants, particularly endocrine disrupters. On the basis of the present results it is quite evident that regenerative response is especially sensitive and that exposure to these types of toxic chemical can induce significant variations in times and modalities of regenerative developmental compared to normal regeneration
Mechanical adaptability of a sponge extracellular matrix: evidence for cellular control of mesohyl stiffness in Chondrosia reniformis Nardo.
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A dynamic model for predicting chemical concentrations in water and biota during the planning phase of aquatic ecotoxicological tests.
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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