1,720,988 research outputs found
The spherule cells of Holothuria polii Delle Chiaie, 1823, (Aspidochirata, Holothuroidea) during brown body formation: an ultrastructural study.
No full textSpherule cells are specific types of coelomocytes found in both the coelomic fluids and the connective tissues of many echinoderm groups and are characterised by large membrane-bound inclusions which completely fill their cytoplasm. In holothurians they are present in massive number in the coelomic fluids and are employed in brown body formation. Brown bodies are products of encapsulation and mainly consist of phagocytic amoebocytes and spherule cells: they surround foreign particles too large to be ingested by circulating phagocytes. During brown body formation, phagocytic amoebocytes flatten out over the surface of foreign particles to form unpigmented nodules which eventually aggregate into a single brown body in which many spherule cells are entrapped. Morphological modifications of spherule cells were studied in Holothuria polii following the induction of brown body formation by intracoelomic injection of sheep erythrocytes. Our ultrastructural observations provide evidence that the granules undergo typical exocytosis after previous disorganisation of their content and suggest a specific secretory activity for the spherule cells. The possible functional role of the secreted vacuolar material in brown body formation is discussed
Mechanical adaptability of a sponge extracellular matrix: evidence for cellular control of mesohyl stiffness in Chondrosia reniformis Nardo.
No full textPCB-induced environmental stress and the regenerative response in crinoids
No full textEchinoderm regeneration provides a convenient and tractable test to monitor the effects
of persistent micropollutants on the developmental physiology of marine animals. Regeneration
involves crucial and sensitive biological processes (cell proliferation, morphogenesis, differentiation,
tissue renewal) that make it an ideal tool to assess micropollutants at the tissue and cellular level. Our
results provide evidence that the regenerative response in the crinoid Antedon mediterranea is especially
sensitive to PCBs and that exposure to these chemicals induces significant variations in timing
and modality of arm regeneration. Prolonged exposure to low concentrations of Aroclor®1260 (14 ngl–1 of total PCBs), typical of moderately polluted coastal zones, results in abnormal arm growth in
terms of both gross morphology and microscopic anatomy. In terms of tissue/cellular aspects the main
modifications are: accelerated growth of the regenerate; massive cell migration/proliferation; hypertrophic
development of the coelomic canals; and, extensive rearrangement of differentiated tissues of
the stump. The anomalies observed in the developmental regenerative processes appear to be compatible
with a pattern of pseudo-endocrine activities
Changes in ubiquitin conjugates and Hsp72 levels during arm regeneration in echinoderms
No full textAll organisms show a common defensive mechanism that results in the expression of conserved heat shock proteins (Hsps). These proteins function in a wide range of stressful conditions. We have monitored their levels in species of regenerating echinoderms with different mechanisms of regeneration and from different geographical locations. The effect of an artificial higher temperature on expression of Hsps was also studied. Two stress proteins (Hsp72 and ubiquitin) that are important in processes such as development and protein degradation were investigated. Using Western blot analysis and immunocytochemistry, we found significant changes in the level (Hsp72) and pattern of conjugation (ubiquitin) that corresponded with the repair phase (early regenerative stages) and with the later growth and regeneration of new tissues. Animals from the intertidal environment showed a distinctly sustained expression pattern of Hsp72 compared with benthic animals which suggests a functionally adaptative and dynamic stress response program
Dynamic structure of the mesohyl in the sponge Chondrosia reniformis (Porifera, Demospongiae)
No full textMuscle growth in response to changing demands in the teleost Sparus aurata (L) during development from hatching to juvenile.
No full textGrowth of laterarl muscle in the teleost fish
Sparus aurata (L.) was examined from hatching to juvenile
by a basic morphofunctional approach that takes into
account structural and ecophysiological aspects and
combines in vivo observations and LM and TEM microscopic
analysis. As shown in most teleost fishes, muscle
growth proceeds by a double mechanism of hyperplasia
and hypertrophy that contribute differentially to the overall
development of the lateral muscle, giving rise in each
myomere to a typical pattern of structurally and functionally
different fibre types (slow-red and fast-white fibres,
plus pink intermediate fibres) in a nerve-dependent
process. During larval life the muscle growth takes place
mainly due to hyperplastic growth at the level of specific
proliferative zones of the myomeres, from which slow,
pink and white muscle fibres are derived. In those species
that reach a large adult size a new typical hyperplastic
process disseminated throughout the fast white muscle
layer takes place during post-larval life. In contrast,
hypertrophic growth occurs in all stages, but is the dominant
mechanism of muscle growth only in juvenile and
adult. The suitable recruitment of the different fibre
types enables the fish to optimize its performances according
to specific functional and metabolic requirements
related to the swimming behaviour and hydrodynamic
regimes. The different mechanisms of growth are
here analysed in their detailed structural and ultrastructural
aspects in order to interpret their adaptive significance
in the light of the fish life cycle, with particular
reference to locomotion and feeding behaviou
A dynamic model for predicting chemical concentrations in water and biota during the planning phase of aquatic ecotoxicological tests.
No full textThe spherule cells of Holothuria polii Delle Chiaie, 1823, (Aspidochirata, Holothuroidea) during brown body formation: an ultrastructural study
No full textSpherule cells are specific types of coelomocytes found in both the coelomic fluids and the connective tissues of many echinoderm groups and are characterised by large membrane-bound inclusions which completely fill their cytoplasm. In holothurians they are present in massive number in the coelomic fluids and are employed in brown body formation. Brown bodies are products of encapsulation and mainly consist of phagocytic amoebocytes and spherule cells: they surround foreign particles too large to be ingested by circulating phagocytes. During brown body formation, phagocytic amoebocytes flatten out over the surface of foreign particles to form unpigmented nodules which eventually aggregate into a single brown body in which many spherule cells are entrapped. Morphological modifications of spherule cells were studied in Holothuria polii following the induction of brown body formation by intracoelomic injection of sheep erythrocytes. Our ultrastructural observations provide evidence that the granules undergo typical exocytosis after previous disorganisation of their content and suggest a specific secretory activity for the spherule cells. The possible functional role of the secreted vacuolar material in brown body formation is discussed
Expression studies on homeobox and bmp homologues in echinoderm neuronal regeneration
No full textRecent years have seen an expansion of interest in the use of echinoderms as models for the study of gene expression in development. In particular, emphasis has been placed on patterning genes and their role in the determination cell lineage and fate.
In our laboratory, we have focussed on the remarkable powers of regeneration exhibited by this invertebrate phylum with close phylogenetic links to chordates.
Our investigations have involved cloning a BMP2/4 homologue from crinoids (AnBMP2/4) and the identification of a number of homeobox homologues in asteroids.
In situ hybridisation indicates an important role for AnBMP2/4 during the early stages of blastemal regeneration at a time when fundamental patterns are being established. AnBMP2/4 expression was first detected in cells from the coelomic epithelium, and subsequently in coelomocytes of the regenerating blastema. To date, the function of BMP2/4 found in other system, as well as AnBMP2/4, as a neural inhibitor or an epidermal inducer is under investigation. However, this expression in an adult system shows similarities with recent studies 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.
In asteroids we have cloned a number of Hox genes including homologues of Hox1, Hox4/5, SpHbox1/TgHbox1, Hox9/10, Gbx and, uniquely a Mox homologue. These have all been identified by RT-PCR in cDNAs prepared from regenerating radial nerve cord (RNC) at days post ablation (pa). Immunocytochemistry using an antibody against the product of Hox1 homologue has revealed its expression pattern during neural regeneration, particularly at day 10, in Asterias rubens
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