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The reaction of the colonial ascidian Botryllus schlosseri to allogeneic blood. Preliminary results.
No full textLa determinazione dell'asimmetria bilaterale nei blastozooidi di Botryllus schlosseri. Analisi sperimentale
No full textSexual differentiation and germ cell transfer in the colonial ascidian Botryllus schlosseri
Full text linkThe sexual differentiation in the colonial ascidian Botryllus schlosseri was considered with respect to colony sexualization and sexualization of the single zooids of the same blastogenic generation. The colony sexualization was investigated histologically in a series of young colonies reared in the laboratory and fixed periodically throughout a sequence of blastogenic generations. The newly set colonies lack gonad blastemata; next, germ cells appear and several generations are involved in various phases of hyposexuality prior to the appearance of generations in which mature both eggs and sperm. The sexual contribution of the zooids of the same generation was found to vary according to an intrinsic bilateral asymmetry (the gonadogenic potential differs both contralaterally in each zooid and between zooids of a different, dextral or sinistral, parental origin) and in proportion to the quantity of germ cells that have been transferred from preceding generations. The transfer of germ cells from one to the following generations was investigated by fusing colonies of opposite pigment genotypes, then crossing the separated parabionts to a common genotype, and scoring the offspring pigment phenotypes. This experiment has shown that not only immature oocytes but also undifferentiated cells were exchanged between the parabionts and then gradually matured as eggs or sperm in a prolonged series of generations. The primordial germ cells differ in size from hemoblasts, the source of hemocytes. However, further experiments are needed in order to decide between the two contrasting hypotheses of germ cell origin: either segregation from the atrial epithelium of buds or development from hemoblasts
New data on phagocytes and phagocytosis in the compound ascidian Botryllus schlosseri (Tunicata: Ascidiacea)
Full text linkIn the compound ascidian Botryllus schlosseri, phagocytes change their morphology and frequency during the colonial blastogenic cycle. In the regression phase, characterized by intense phagocytosis, zooids of the old generation are progressively resorbed, the frequency of hyaline amoebocytes falls abruptly, and the frequency of macrophage-like cells increases significantly. Moreover, the hyaline amoebocytes engulf foreign materials, withdraw their cytoplasmic projections, and change their shape from flat and fusiform to spherical or ovoidal: all these processes suggest that hyaline amoebocytes represent the precursors of macrophage-like cells. During regression, a significant increase in blood levels of hydrogen peroxide and acid phosphatase is observed, in agreement with data obtained in in vitro experiments showing an increase in reactive oxygen metabolite production, nitrite ion release, and acid phosphatase secretion associated with phagocytosis
A soluble, beta-galactoside specific agglutinin acts as opsonin in the colonial ascidian Botryllus schlosseri
No full textCalcium homeostasis and yeast phagocytosis in hemocytes of the colonial ascidian Botryllus schlosseri
Full text linkThis paper reports the effects of drugs affecting the homeostasis of cytosolic-free calcium on in vitro yeast phagocytosis by hemocytes of the colonial ascidian Botryllus schlosseri. Significant inhibition of phagocytosis is observed after exposure of hemocytes to 10 μM or higher concentrations of thimerosal, which is known to deplete intracellular calcium stores in mammalian cells. The two calcium channel blockers nifedipine and verapamil significantly decrease the phagocytic index, the minimum effective concentrations being 10 and 50 μM, respectively. As these substances have no effects at lower concentrations, they probably act through the inhibition of Ca2+-ATPase activity, required to restock intracellular calcium stores, due to their interaction with calmodulin. Analogously, pimozide, which suppresses ATPase activity by interacting with calmodulin, and thapsigargin, which inhibits Ca2+-ATPase activity, significantly reduce the phagocytic index. Moreover, nifedipine, by altering cytosolic calcium homeostasis, also lowers the production of superoxide anion associated with phagocytosis. Results indicate that in ascidians, as in mammals, a rise in intracellular calcium is required for phagocyte activation and induction of the respiratory burst
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