1,721,067 research outputs found
Morphological observations on the zooid regression of the colonial ascidian Botryllus schlosseri
Full text linkRGD-containing molecules induce macropinocytosis in ascidian hyaline amoebocytes
No full textPhagocytes of the compound ascidian Botryllus schlosseri are capable of constitutive macropinocytosis (MP) at sites of membrane ruffling along the leading edge. This gives rise to the formation of initially irregular vesicles which then move to the inside of the cells and acquire a more regular morphology. Both phagocyte spreading and MP are enhanced by the recognition of molecules containing the sequence Arg-Gly-Asp (RGD): this suggests that, as in mammals, integrin activation is involved in the induction of both cell spreading and endocytosis. The occurrence of MP is associated with increased oxygen consumption and a rise in the production of superoxide anion, as indicated by nitroblue tetrazolium reduction, and ATP, as indicated by increased cytochrome oxidase activity. On the whole, our results indicate the conservation of common mechanisms of MP induction throughout the Chordate phylum
Common and divergent pathways in alternative developmental processes of ascidians
Full text linkColonial ascidians offer opportunities to investigate how developmental events are integrated to generate the
animal form, since they can develop similar individuals (oozooids from eggs, blastozooids from pluripotent
somatic cells) through very different reproductive processes, i.e. embryogenesis and blastogenesis. Moreover,
thanks to their key phylogenetic position, they can help in the understanding of the molecular mechanisms of
morphogenesis and their evolution in chordates. We review organogenesis of the ascidian neural complex
comparing embryos and buds in terms of topology, developmental mechanisms and terminology. We propose
a new interpretation of bud territories, and reconsider nervous system development based on recent results
suggesting that ascidians have vertebrate placodal and neural-crest-like cells. Comparing embryonic and blastogenic
development in Botryllus schlosseri, we propose that the bud has territories with a placodal potentiality,
suggesting that chordate ancestors possessed neurogenic placodes, and that the genetic pathways regulating
neurogenic placode formation were co-opted for new developmental processes, such as blastogenesis
Tunicata and Cephalochordata
No full textTunicata and Cephalochordata, collectively named Protochordata, are filter-feeding marine animals which, as invertebrate members of the phylum Chordata, share with vertebrates the basic chordate characteristics. Tunicata are found at all latitudes and can assume a planktonic or benthic lifestyle. Coloniality is widespread and a larval stage followed by metamorphosis is the rule in the class Ascidiacea. Blooms of pelagic tunicates are quite common in warm seasons: their ecological relevance relies on the key role played by these animals in the alimentary chain of open seas. Cephalochordata are small, fish-like animals living in sandy bottoms, of interest for evolutionary studies
L'organo coronale delle ascidie e l'evoluzione della cellula sensoriale secondaria nei Cordati
No full textTissue repair during egg segregation in tunic of the compound ascidian, Diplosoma listerianum
No full textIn D. listerianum mature eggs are isoltaed in the tunic where embryos develops. The process of egg segregation was studied by light and electron microscopy. Initially the egg is contained in a sac-like pocket of the epidermis which narrows to form an ephemeral collar at its proximal end. The follicle cells discharged from the egg are retracted towards the zooid to block the aperture of the collar. The epidermis breaks close to the egg and the lips of the wound heal rapidly, enclosing the egg in the tunic and later re-establishing the epidermal continuity of the zooid. Both granulocytes form the bloodstream and epitheliocytes engulf tissue debris. Moreover, apocrine secretion of the epidermis participates in tunic restoration. The permeability barrier of the zooid seems to be assured by tight junctions, together with the plug of follicle cells
Hibernation of the colonial ascidian Botrylloides leachi (Savigny): histological observations
Full text linkIn a previous paper the biological cycle of the colonial ascidian Botrylloides leachi, in the Laguna Veneta, was described (BRUNETTI 1976). Such research indicated that during the winter this ascidian undergoes a process of hibernation, which resembles, in some respects, that described by BANCROFT (1903) as “aestivation” in a colony of Botrylloides gascoi (synonymous with Botrylloides leachi, see SALFI, 1931). During hibernation the colony lacks filtering zooids and resembles a homogeneous carpet of ampullae which is usually covered by diatoms and detritus. In spring, with a rise in temperature new zooids are formed, these emerge from the tunic, and gradually reconstruct new “ladder systems”. Due to the opacity resulting from the high density of pigmented cells, the events occurring within the colony during hibernation and vernal reactivation are not easily observed “in vivo”. To overcome this difficulty we have performed a histological study on colonies collected at various periods in order to determine the more characteristic features of this process and follow them in greater detail than is possible with living material
Studies on macrofouling biocoenosis of hard substrates for the estimation of the environmental quality in the Lagoon of Venice.
No full textThe study of the development of macrofouling biocoenoses is of particular interest because it might represent an instrument for the evaluation of the biodiversity. In the lagoon of Venice, these studies acquire a critic relevance owing to they allow to reveal, in the long term, quality and quantity changes of the fouling community attributable to environmental differences and improve the comprehension of the existing interactions between the organisms of the fouling and some physical-chemical factors of seawater and/or xenobiotics. We carried out an analysis of the temporal sequence of the macrofouling biocoenosis of hard substrates in the southern basin of the lagoon of Venice on steel and wood panels, with the aim of developing an environmental quality index (bioindex) which was cheap, easy to calculate, sensitive to many environmental conditions and considering the relationships between the biotic data and change of highly significant chemical-physical parameters as regards the lagoon environment. It is specific for the community of hard substrates, and represented by the following algorithm:
Log10 ( R • A • IpH • IT • IS )
where R = species richness, i.e., number of species by month present onto all panels of the same type; A = area extension for each species by months (cm2); IpH = pH quality index; IT = temperature quality index; IS = salinity quality index.
The development of a quality index in logarithmic scale, from 1 to 10 inclusive, allows to really evaluate the state of health of the lagoon environment assigning to it a numerical value.
Moreover, we investigated the disturbing action on “Botryllus biocoenosis”, a benthic association of various ascidians where the colonial species are dominant, by eight antifouling paints of new generation containing Cu2O, CuO, CuSCN, Sea-Nine 211, Irgarol 1051, Diuron, Chlorothalonil, Dichlofluanid, Zinc pyrithione, Zineb and Endosulfan as principal or booster biocides. Experiments were carried out on wood and steel panels immersed for one year in two stations of the southern basin, differing in bathymetric, hydrodynamic and turbidity characteristics. The growth and development of biocoenoses were analysed monthly and compared with both control and TBT-treated panels. Biodiversity indexes – species richness, biocoenosis structure, Benninghoff’s covering-abundance index, and Sørensen’s similarity index – were used to describe the evolution of the biocoenosis and compare the disturbing effects resulting in the selection of resistant species, often different from those of the natural relative climax. Results indicate that none of the assayed paints is more powerful than TBT-containing paints and the effects on the biocoenosis are potentiated by the type of matrix and presence of booster compounds, following the order of biocidal efficacy of paints containing TBT > organozinc > copper > Sea-Nine
Aspetti morfo-funzionali dell'epitelio digestivo in Appendicolarie (Urochordata)
No full textLe Appendicolarie, tunicati planctonici, costruiscono ciclicamente un sistema esterno "usa e getta", molto specializzato per la cattura del cibo, svolgendo un ruolo fondamentale nel trasferimento di energia attraverso le catene trofiche degli oceani. A differenza degli ascidiacei, ben poco si conosce sul loro tubo digerente. Di questo abbiamo ora studiato l'organizzazione e l'ultrastruttura comparandole a quelle degli ascidiacei. Nelle Oikopleuridae il tubo digerente comprende un esofago tubolare, uno stomaco sacciforme suddiviso in due lobi diversificati e un intestino ad U, diviso in prossimale-medio e retto, privo di ghiandola pilorica e terminante con un ano tra i due spiracoli. Rispetto agli ascidiacei mancano le cellule mucose, le cellule endocrine, le cellule plicate e i centri proliferativi. La propulsione del cibo e la formazione dei pellet avvengono ad opera di cellule cigliate a microvili che nell'esofago producono unasecrezione densa, mentre nello stomaco e nell'intestino sono anche assorbenti e presentano profonde interdigitazioni baso-laterali di membrana associate a mitocondri con probabile ruolo di regolazione osmotica. Nello stomaco la digestione è a carico delle cellule basofile che, diversamente dalle ascidie, sono raggruppate in una banda gastrica nel lobo sinistro. Cellule a globi nello stomaco e nel retto assorbono per pinocitosi macromolecole quali la perossidasi. L'apparente semplificazione strutturale è in linea con l'economia organizzativa delle appendicolarie e permette comunque un'alta efficienza nel trattamento del cibo per soddisfare le elevate richieste energetiche del loro rapido ciclo vitale
A tale of death and life: natural apoptosis in the colonial ascidian Botryllus schlosseri (Urochordata, Ascidiacea).
No full textThe colonial ascidian Botryllus schlosseri forms new zooids by blastogenesis, through the formation of palleal buds which progressively grow and mature until adults are formed. At a temperature of 19°C, adult zooids remain active for about one week; then they contract, close their siphons and are gradually resorbed, being replaced by buds which reach functional maturity, open their siphons and begin their filtering activity as adult zooids. This recurrent generation change, known as take-over, is characterised by the occurrence of diffuse programmed cell death by apoptosis. Immediately before the take-over, an increase in the expression of molecules recognised by anti-Bax antibodies and a parallel decrease in the expression of molecules immunopositive to anti-Bcl-2 antibodies were observed in zooid tissues, suggesting a mitochondrion-dependent apoptotic pathway. During the take-over, circulating phagocytes infiltrate the zooid tissues and engulf apoptotic cells; in addition, the frequency of haemocytes showing nuclear condensation and annexin-V labelling significantly increases. Previous experiments showed the involvement of phosphatidylserine and CD36 in the recognition of effete cell. The resorption of old zooids is closely related to the rejuvenation of the colony occurring at the take-over. The death of adult zooids puts a quantity of material at the colony disposal. This material is represented by senescent cells, which, once ingested and digested by phagocytes, can be recycled and used to sustain the burden of blastogenesis: this involves a cross-talk between old tissues, phagocytes and developing buds. Therefore, B. schlosseri can be considered a new and promising model organism for the study of natural apoptosis
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