Complete 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).
Stress and regeneration in crinoids and asteroids
PATRUNO, MARCO VINCENZO;
1998
Abstract
Complete 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).Pubblicazioni consigliate
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