G. Van de Vyver

An experimental study of the life-cycle of the fresh-water spongeEphydatia fluvitilis in its natural surroundings

SummaryThe life cycle of three strains of the fresh-water spongeEphydatia fluviatilis, experimentally cultivated in a pond near Brussels has been studied.The complete experiment lasted four consecutive years.Seasonal histological fluctuations are described. They emphasise that this species overwinters in a highly disorganized stage and completely regenerates in the early spring.These observations constitute a first approach to the analysis of the induction mechanisms of sexual reproduction.They clearly indicate the necessity for the sponge to overwinter in the field, in order to be able to undergo a sexual reproduction. It is to be noted that the first oocytes appear every year at the beginning of the winter, a little while after the sponges have reached their typical disorganized stage.The stability of the strain throughout sexual reproduction is demonstrated.ZusammenfassungDer Lebenszyklus dreier Stamme des SüßwasserschwammesEphydatia fluviatilis, experimentell kultiviert in eimem Teich bei Brüssel, wurde untersucht. Die Untersuchung zog sich über vier Jahre hin.Saisonabhängige histologische Veränderungen werden beschrieben. Sie zeigen, daß diese Art in völlig unorganisiertem Zustand überwintert und im frühen Frühling regeneriert wird.Diese Beobachtungen bilden einen ersten Schritt in Richtung auf die Analyse der Induktionsmechanismen der sexuellen Fortpflanzung. Sie zeigen, daß der Schwamm zu seiner sexuellen Fortpflanzung notwendigerweise in der natürlichen Umgebung überwintern muß. Bemerkenswert ist, daß die ersten Oocyten jährlich zu Beginn des Winters auftreten, kurz nachdem die Schwämme ihr typisches, unorganisiertes Stadium erreicht haben.Die Stabilität der Stamme über die sexuelle Fortpflanzung hinaus wird nachgewiesen.

Localization and ecological significance of oroidin and sceptrin in the Caribbean sponge Agelas conifera

The Caribbean sponge Agelas conifera was found to produce a mixture of previously described bromopyrrole alkaloids of which oroidin (1) and sceptrin (2) were predominant. This sponge harboured large populations of heterotrophic bacteria but no photosynthetic symbionts (cyanobacteria). However, 1 and 2 were not associated with the bacteria but with the sponge cells as shown by their distribution in enriched cell fractions obtained by differential centrifugation and Ficoll density gradients. Spherulous cells, found in great abundance in the sponge ectosome, were assumed to be involved in the production of 1 and 2. The target compounds were detected, although in small amounts, in short-term cultures of sponge cells, validating the possibility of a continuous cell culture source. Laboratory assays showed that organic sponge extracts affected the behaviour of the coral Madracis mirabilis in causing closure and retraction of the polyps at concentrations of the combined compounds 1 and 2 (1:3.3) as low as 0.7 mg/l (0.0125% of the concentration in whole sponges). At higher concentrations (1.4 mg/l) no recovery of the polyps occurred. The extracts, at almost natural concentrations of 1 and 2, deterred feeding by the predatory reef fish Stegastis partitus, supporting other reported research. In field experiments, wounding induced a sharp increase of 1 and 2 in the sponge tissues but prolonged predator exclusion by caging and forced confrontation with coral neighbours did not yield measurable changes in 1 and 2 concentrations. All sponges were found to release measurable amounts of bromopyrrole alkaloids in seawater conditioned for 30 min. Crude and fractionated sponge extracts and pure sceptrin (2) were active against bacteria, yeast and filamentous fungi. Taken together, these results support a role of oroidin (1) and sceptrin (2) in defence mechanisms against predators and possibly against space competitors and invading and fouling organisms.

Chapter 4 Phenomena of Cellular Recognition in Sponges

Publisher Summary This chapter discusses the phenomena of sponge cell recognition. When fully grown sponges belonging to the same species are brought into contact, either naturally or by an experimental process, they fuse into a single organism. In the absence of any circulatory system, the ability for cellular recognition resides in the cell surface and is expressed when cells come into contact. This characteristic of sponges and the readiness, with which the sponges can be dissociated into cellular suspension, led to the main experimental work on cellular recognition in these organisms— that is, the studies on the aggregating behavior of dissociated sponge cells. The technique of cell aggregation is very useful, as it allows the mixing of cell suspensions of different kinds and proportions, and because a large number of cells can be brought simultaneously into contact. Purification and characterization of sponge cell aggregating factors was first attempted in Microciona prolifera and Haliclona occulata. Glycopeptides extracted from whole sponges with trichloroacetic acid were antigenic and that they elicited in rabbits precipitating and agglutinating antisera specific for the homologous cells. Some phenomena, involved in sponge cell recognition, were investigated during the reaggregation of the dissociated cells. It is pointed out that in sponges cell, recognition occurs at three levels—namely, cell type specificity, intraspecific recognition, and interspecific recognition.

Endocytosis of latex beads by the exopinacoderm in the fresh water sponge Ephydatia fluviatilis: an in vitro and in situ study in SEM and TEM.

Endocytosis capability of the dermal membrane of Ephydatia fluviatilis has been demonstrated in vitro and in situ using two different sizes of calibrated Latex beads. After a preliminary adhesion to the cell coat, 5.7- and 0.109-μm beads were endocytized by exopinacocytes. Some ingestion mechanisms appeared to depend upon particle size. In vitro, with 0.109-μm beads, the exopinacocyte cell surface creased, forming ruffles in the central area of the cells. In vitro and in situ, 0.109-μm beads were observed to slip through gaps in the dermal membrane. In addition to their conventional role as an inhalent pore, porocytes were shown to possess a particle retention ability, which remained even in the case of complete closure of the ostia. Endocytosis, occuring on the whole sponge surface, points out the importance of exopinacocytes in particle retention, bypassing the choanocytes in their capture role.

Aggregative properties of different cell types of the fresh-water spongeEphydatia fluviatilis isolated on ficoll gradients

Cell suspensions of the fresh-watersponge Ephydatia fluviatilis have been fractionated by means ofFicoll gradient centrifugation. Three fractions were isolated. The densest contains archeocyte-like cells only; the intermediate fraction is very rich in choanocytes, and the lightest is a mixture of cell types. Earch fraction shows specificaggregative properties and potentialities to reconstitute functional sponges.It appears that the sequence of reconstitution events can be selectively altered by certain disequilibria in the cell populationThese preliminary results constitute a first approach to the analysis ofcell type specificity in sponges.SummaryCell suspensions of the fresh-watersponge Ephydatia fluviatilis have been fractionated by means ofFicoll gradient centrifugation. Three fractions were isolated. The densest contains archeocyte-like cells only; the intermediate fraction is very rich in choanocytes, and the lightest is a mixture of cell types. Earch fraction shows specificaggregative properties and potentialities to reconstitute functional sponges.It appears that the sequence of reconstitution events can be selectively altered by certain disequilibria in the cell populationThese preliminary results constitute a first approach to the analysis ofcell type specificity in sponges.

Homeobox-Containing Genes in Freshwater Sponges: Characterization, Expression, and Phylogeny

The mono- or polyphyletic origin of metazoans has been discussed for a long time because morphological and embryological data are insufficient to discriminate between these alternative hypotheses. The advent of molecular biology and molecular phylogeny with the development of sequencing and the polymerase chain reaction (PCR) has brought some light to this controversy, although molecular data have sometimes led to conflicting interpretations (Field et al. 1988; Lake 1990; Christen et al. 1991; Kobayashi et al. 1993; Wainright et al. 1993; Rodrigo et al. 1994). At present, the monophyly of metazoans is widely accepted, but the phylogenetic position of sponges, considered to be the most primitive metazoan phylum, remains controversial (Muller et al. 1994a; Muller 1995).

Ultrastructural localization of lysosomal digestion in the fresh water sponge Ephydatia fluviatilis

The digestive capabilities of endocytizing cells of Ephydatia fluviatilis have been determined by the ultrastructural localization of acid phosphatase. Two distinct markers of endocytic activity were supplied to sponges grown in vitro: Latex beads and Escherichia coli. With both markers, an enzymatic activity was found in lysosomes and in phagolysosomes, as well in archaeocytes and choanocytes, as in exo- and endopinacocytes of the dermal membrane, pointing out that each cell type is capable of feeding itself. The digestive capabilities of each cell type were confirmed by the alteration of the bacteria in phagolysosomes. This localization of lysosomal activity, coupled with the endocytosis of particles clearly revises the previously accepted idea that archaeocytes are the sole digesting cells, this function being also supported by the choanocytes and the pinacocytes. The digestive capacity of the exo- and endopinacocytes confirms the importance of the dermal membrane, bypassing the choanocytes not only in their capture role, but also in their digestive role.

A quantitative study of the retention of radioactively labeled E. coli by the freshwater sponge Ephydatia fluviatilis

In this method designed to quantify the amount of bacteria retained by sponges, young Ephydatia fluviatilis raised in vitro were provided with E. coli grown in the presence of ³H-labeled thymidine. The maximal retention capacity was reached after 15-24 h and was followed by a loss of radioactivity at a steady rate. The nonspecific adhesion of bacteria to the substratum remained close to 10% for 15 h and increased to as much as 43% by 24-48 h. Sponges provided repeatedly with bacteria showed a higher retention capacity, suggesting the efficiency of the bacterial nutrition. Transmission electron microscopy and scanning electron microscopy showed that, after a preliminary adhesion to the choanocytes and exopinacocytes, bacteria were engulfed in individual phagosomes, which later fused together. The quantitative method established in this paper should prove useful for further studies of the retention of any particulate matter by sponges.