1,721,003 research outputs found
Spermatogenesis as a tool for staging gonad development in the gonochoric appendicularian Oikopleura dioica Fol 1872
No full textOikopleura dioica, the only gonochoric species among appendicularians, has a spematozoon with a mid-piece
and a conspicuous acrosome that, during fertilisation, undergoes a reaction forming an acrosomal process. To
provide more insight into the spermatogenesis of a holoplanktonic tunicate species that completes its life cycle
in three to five days, changes in the testis during individual growth have been examined. Spermatogenesis has
been subdivided into seven stages based on ultrastructural features during the formation and organisation of the
male gonad and the relationships between its macroscopic anatomy and the events of sperm differentiation.
Gametes undergo highly synchronised differentiation due to the presence of widespread syncytial structures.
Both meiosis and spermiogenesis are brief, and the passage from spermatocytes to spermatids involves a
progressive segregation of the germ cells from the syncytial mass with the formation of large cytoplasmic
bridges and volume reduction for nucleus compacting and cytoplasmic material changing. The nucleus is small
and penetrated anteriorly by a complex acrosome and posteriorly by the distal centriole and part of the
flagellum. In spermatids, the single, large mitochondrion appears laterally to the nucleus, and finally, in
spermatozoa, it migrates into the mid-piece, wrapping the proximal portion of the axoneme. Because this
mitochondrial position is reached only in the late phases of spermatogenesis, it suggests that appendicularians
have derived oligopyrenic sperms in which the small nucleus results from adaptation to the assembly of
numerous spermatozoa inside the narrow space of the testis compacted in the genital cavity. The formulation of
a staging system of gonad development in a model tunicate species known for having the most compacted
genome in chordates led to a comparison of histological observations with recent molecular data, improving the
characterisation of its biology and life cycle in light of evolutionary implications
Searching for the Origin and the Differentiation of Haemocytes before and after Larval Settlement of the Colonial Ascidian Botryllus schlosseri: An Ultrastructural Viewpoint
Full text linkThe colonial ascidian Botryllus schlosseri possesses an innate immunity, which plays fundamental roles in its survival, adaptability, worldwide spread and ecological success. Three lines of differentiation pathways of circulating haemocytes are known to be present in the haemolymph, starting from undifferentiated haemoblasts: (i) the phagocytic line (hyaline amoebocytes and macrophage-like cells), (ii) the cytotoxic line (granular amoebocytes and morula cells) and (iii) the storage cell line (pigment cells and nephrocytes). Many questions remain about their origin, and thus, observations
during various stages of development were undertaken in this study. Haemocytes were detected beginning from the early tailbud embryo stage. Haemoblasts were always present and morula cells were the first differentiated haemocytes detected. In both the next stage, just before hatching, and the swimming tadpole larva stage, hyaline amoebocytes and pigment cells were also recognisable.
Some morula cells containing active phenoloxidase migrated from the haemolymph into the tunic after having crossed the epidermis, and this behaviour could be related to the preparation of a defensive function for spatial competition. During larval metamorphosis, macrophage-like cells appeared with their phagosomes positive to acid phosphatase activity and containing apoptotic cells from tail tissue degeneration. After metamorphosis, in the filter-feeding oozoid stage, nephrocytes involved in nitrogen catabolism finally appeared. In both the subendostylar sinus and the peripheral blind-sac vessels (ampullae), clusters of haemoblasts were recognisable, some of which showed incipient specialisations, considering the hypothesis of the presence of putative niches of haemolymph stem cells
Potential disruptive effects of copper-based antifouling paints on the biodiversity of coastal macrofouling communities
Full text linkThe expanded use of copper(I)-based antifouling paints (AF) has increased copper leaching into coastal environments, requiring attention and legislative restrictions for potential long-term effects on benthic populations. The ecological succession of macrofouling communities was analysed on wooden and stainless steel panels coated with four copper(I)-based AF (Paints A–D) immersed for 10 months in the Lagoon of Venice. With the exception of Paint B, which contained only copper(I) compounds and was based on hard-matrix technology, the other paints were based on self-polishing matrices and various booster biocides. The booster content was a mix of TBT compounds for Paint A, dichlofluanid for Paint C, Irgarol 1051, and chlorothalonil for Paint D. The macrofouling communities appeared dissimilar to those on the reference uncoated panels as regard the species richness, the coverage areas, and the biocoenosis structure. Generally, green algae, bryozoans, and barnacles were the most tolerant taxa and a negative species selection occurred for sponges, serpulids, and ascidians. Paints A and D showed the highest performance, and Paint D also prevented molluscs on wood panels. Paints B and C rapidly decreased their efficiency, the first probably due to the insoluble matrix with the highest biocidal leaching rate, and the second due to the presence of a booster with low toxicity. Paint B also inhibited red algae and molluscs, but Paint C did not reveal significant differences in types of species settlements with reference panels
Immunotoxic effects of a new-generation antifouling biocide in a compound ascidian.
No full textDichlofluanid has long been employed as a fungicide in agriculture and has been massively introduced in antifouling paints for boat hulls over the last two decades. One of the most important toxic effects of antifoulants is represented by immunosuppression in marine invertebrates, which can be analysed in vitro with a number of short-term toxicity assays on haemocytes. Among bioindicators, the colonial ascidian Botryllus schlosseri is a useful candidate; it is a filter-feeding organism living in the water-sediment interface that is found worldwide and is sensitive to antifouling xenobiotics. Dichlofluanid adversely affects both immunocyte lines (phagocyte and cytotoxic lines) after exposure to sublethal concentrations. At 0.05 μM (16.65 μg/l), dichlofluanid induced haemocyte apoptosis and cell shrinkage with a decrease in both motility and phagocytosis. At the lowest concentration (0.01 μM, 3.33 μg/l), inhibition of pivotal enzymatic activities of phagocytes and cytotoxic cells occurred. At the highest concentration (0.1 μM, 33.3 μg/l), dichlofluanid increased glutathione oxidation, leading to stress conditions. The effects of dichlofluanid on immune defence responses are similar to those of organometal-based antifoulants (i.e., organotin compounds and zinc pyrithione), and its use in coastal areas requires attention
Larval Settlement on Marine Surfaces: The Role of Physico-Chemical Interactions
Full text linkBiofouling is the association of sessile aquatic organisms that rapidly settle on artificial hard substrata, thereby posing a large problem worldwide since its growth often causes severe damage to submerged structures [...
Botryllin, a Novel Antimicrobial Peptide from the Colonial Ascidian Botryllus schlosseri
Full text linkBy mining the transcriptome of the colonial ascidian Botryllus schlosseri, we identified a transcript for a novel styelin-like antimicrobial peptide, which we named botryllin. The gene is constitutively transcribed by circulating cytotoxic morula cells (MCs) as a pre-propeptide that is then cleaved to mature peptide. The synthetic peptide, obtained from in silico translation of the transcript, shows robust killing activity of bacterial and unicellular yeast cells, causing breakages of both the plasma membrane and the cell wall. Specific monoclonal antibodies were raised against the epitopes of the putative amino acid sequence of the propeptide and the mature peptide; in both cases, they label the MC granular content. Upon MC degranulation induced by the presence of nonself, the antibodies recognise the extracellular nets with entrapped bacteria nearby MC remains. The obtained results suggest that the botryllin gene carries the information for the synthesis of an AMP involved in the protection of B. schlosseri from invading foreign cells
An exceptional immunosurveillance system of the pharynx entry in a protochordate
No full textIn the colonial ascidian Botryllus schlosseri, we have recently identified unusual free amoebocytes, completely exposed to the sea-water flow entering into the pharynx, which inhabit the tunic surface that internally covers the oral siphon (Cima et al., 2006 Dev Comp. Immunol., 30: 463-472). All histochemical data support the hypothesis that these cells named “siphonal guard cells” (SGC) belong to the hyaline amoebocyte population of the phagocytic differentiation pathway of the circulating immunocytes. After crossing the epidermis which bounds the siphonal blood sinus, they adhere to strategic points of the tunic and can recognise and phagocytise various foreign particles. After exposure of colonies to bacterial spores, the observations at both light and electronic microscope revealed that these cells are involved in a complex series of local and systemic immune events. Already after 5 min, the SGC show bacteria inside heterophagic vacuoles. After 10-15 min, as a transitory plug of colloidal material rich in heparin and histamine is formed in the siphonal lumen by exocytosis of some SGC, other ones with engulfed bacteria cross the epidermis reaching the siphonal sinus and probably transferring an alert signal; cells of the cytotoxic blood cell line (morula cells) crowd into the siphonal sinus, where most of them are labelled by anti-TNF- and anti-CD57 antibodies and degranulate. After this time, large scavenger phagocytes increase in number in blood circulation, show bacteria engulfed in large phagosomes and are continuously eliminated through the peribranchial chamber and the cloacal siphon with a mechanism which was not previously described
Morula cell activation upon the recognition of bacteria, in the compound ascidian Botryllus schlosseri
No full textTwo faces of geotextiles in cost ecosystems: A matter of anti- or profouling effects.
No full textGeotextile materials that are made from polypropylene, polyester or polyethylene have physical, mechanical and hydraulic properties which are used in coastal protection as an alternative to natural stone, slag, and concrete. In coastal ecosystems, they could reveal different impacts on the biodiversity of resident communities resulting in preventing fouling settlement or favouring dominant species. In the first case, they could represent a new tool as antifouling not-chemical systems alternative to the widely biocide mixtures employed in antifouling paints, since the geotextile fuzzy surface disturb the larva and propagule settlement with continuous micromovements. On the other hand, geotextiles could be used as restoration management of degraded ecosystems by means of their capability to favour the species settlement.
In a 10-month experiment, the colonization of macrofouling organisms on four different nonwoven geotextile substrates was investigated in the Lagoon of Venice, Italy - a particular environment of temperate transitional waters with high biodiversity -, and compared with the colonization on wood as a natural reference substrate. The ecological succession was analyzed monthly beginning from the biofilm formation to the stable coverage of sessile animal and plant species, with particular attention to changes in community structure compared to control panels.
Geotextile fabrics reveal to affect both settlement and growth of the macrofouling depending on their texture and chemical composition: biomass development differed significantly from that of wood. On the geotextiles, the climax of biomass development occurred significantly earlier and reached lower biomass values indicating that nonwoven geotextile substrates support macrofouling communities that display unique properties, such as selected species and low biomass. This pioneering study is a preliminary research that is based on more eco-friendly barriers to the biofouling settlement will provide insights for future studies of selective capacity on settlement and possible applications in the coastal environment
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