The major skeletal elements in the (Porifera) sponges, are spicules formed from inorganic material. The spicules in the Demospongiae class are composed of hydrated, amorphous silica. Recently an enzyme, silicatein, which polymerizes alkoxide substrates to silica was described from the sponge Tethya aurantia. In the present study the cDNA encoding silicatein was isolated from the sponge Suberites domuncula. The deduced polypeptide comprises 331 amino acids and has a calculated size of M r 36 306. This cDNA was used as a probe to study the potential role of silicate on the expression of the silicatein gene. For these studies, primmorphs, a special form of aggregates composed of proliferating cells, have been used. It was found that after increasing the concentration of soluble silicate in the seawater medium from around 1 mm to approximately 60 mm, this gene is strongly upregulated. Without additional silicate only a very weak expression could be measured. Because silica as well as collagen are required for the formation of spicules, the expression of the gene encoding collagen was measured in parallel. It was also found that the level of transcripts for collagen strongly increases in the presence of 60 mm soluble silicate. In addition, it is demonstrated that the expression of collagen is also upregulated in those primmorphs which were treated with recombinant myotrophin obtained from the same sponge. Myotrophin, however, had no effect on the expression of silicatein. From these data we conclude that silicate influences the expression of the enzyme silicatein and also the expression of collagen, (via the mediator myotrophin).
In spite of the fact that cells from the phylum Porifera (sponges) contaln high levels of telomerase activity, no successful approach to cultivate sponge cells has yet been described Telomerase is the enzyme which catalyzes the addition of new telomeres onto chromosome ends which have been lost after each round of DNA synthesis. One reason may be seen in the observation that after dissociation the cells lose their telomerase activity. In addition, no nutrients and metabolites have been identified that would stimulate sponge cells to divide. We report here the culture conditions required for the formation of multicellular aggregates from Suberites domuncula from dissociated single cells; they are termed pnmrnorphs. These aggregates, formed in seawater supplemented with antibiotics, have a tissue-like appearance; they have been cultured for more than 5 mo. Cross sections through the primmorphs revealed an organized zonation into a distinct unicellular epithelium-like layer of pinacocytes and a central zone composed primarily of spherulous cells. After their assoclatlon into primmorphs, the cells turn from the telomerase-negative state to the telomerase-positive state. Important is the finding that a major fraction of the cells in the primmorphs undergo DNA synthesis and hence have the capacity to divide. By applying the BrdU (5-brorno-2'-deoxy-uridine)-labeling and detection assay it is demonstrated that up to 33.8% of the cells in the pnrnmorphs are labeled with BrdU after an incubation period of 12 h. It is proposed that the primmorph system described here is a powerful novel model system to study basic mechanisms of cell proliferation and cell death; it can also be used in aquaculture, for the production of bioactive compounds and as a bioindicator system.
Silicon is, besides oxygen, the most abundant element on earth. Only two taxa use this element as a major constituent of their skeleton, namely sponges (phylum Porifera) and unicellular diatoms. Results from combined cytobiological and molecularbiological techniques suggest that, in the demosponge Suberites domuncula, silicic acid is taken up by a transporter. Incubation of cells with the fluorescent silica tracer PDMPO [2-(4-pyridyl)-5-[[4-(2-dimethylaminoethylaminocarbamoyl)methoxy]phenyl]-oxazole] showed a response to silicic acid by an increase in fluorescence; this process is temperature-dependent and can be blocked by DIDS (4,4-di-isothiocyanatostilbene-2,2-disulphonic acid). The putative NBC (Na+/HCO3-) transporter was identified, cloned and analysed. The deduced protein comprises all signatures characteristic of those molecules, and phylogenetic analysis also classifies it to the NBC transporter family. This cDNA was used to demonstrate that the expression of the gene is strongly up-regulated after treatment of cells with silicic acid. In situ hybridization demonstrated that the expression of the sponge transporter occurs in those cells that are located adjacent to the spicules (the skeletal element of the animal) or in areas in which spicule formation occurs. We conclude that this transporter is involved in silica uptake and have therefore termed it the NBCSA [Na+/HCO3-[Si(OH)4]] co-transporter.
Polychlorinated biphenyls (PCBs) are ubiquitous industrial compounds found in almost every component of the terrestrial and marine ecosystem. Most of the PCB congeners bind to the aryl hydrocarbon receptor and in turn cause expression of stress response genes. Here we report for the first time that PCB 118 acts in the marine sponge Geodia cydoniurn as an inducer of 2 chaperones, the 14-3-3 protein(s) (a protein targeting molecule) and the heat shock protein HSP70 (a chaperone, primarily involved in folding of proteins). While the cDNA encoding the latter protein has been cloned previously, the 14-3-3 cDNA from sponges is reported in this study. The full-length cDNA clone of G. cydoniurn, GC14-3-3, has a size of 912 nucleotides (nt) and contains a 744 nt long potential open reading frame; the relative molecular weight (M,) of the deduced aa sequence is 28 378 Da. The sponge polypeptide is closely related to the deduced polypeptides of the 14-3-3 sequences belonging to isoforms q and y. Using the cDNAs, coding for the 14-3-3 and the HSP70 protelns as well as antibodies raised against these 2 proteins, it was demonstrated that neither chaperone can be detected in the absence of PCB. However, after incubation of sponge tlssue w t h PCB 118 the transcripts of the 2 chaperones are detectable after 12 h, while the corresponding proteins appear after 1 d . Subsequently, the levels of the transcripts and of the proteins increase steably. From these data we conclude that the 2 chaperones, 14-3-3 and HSP70, are useful biomarkers in sponges. Due to the broad cross-reactivity of their antibodies throughout the Metazoa, these chaperones may be useful biomarkers for monitoring environmental contaminants, as shown here for PCB 118, in all organisms.
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