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

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... d 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.