APOPTOSIS IN MARINE SPONGES - A BIOMARKER FOR ENVIRONMENTAL-STRESS (CADMIUM AND BACTERIA)

The marine demosponge Suberites domuncula is abundantly present on mud dy sand bottoms, both in the open sea and in harbors. In the present s tudy it is shown that exposure of S. domuncula to cadmium (CdCl2) in c oncentrations ranging from 0.01 to 5.0 mu g ml(-1) for up to 5 d resul ts in apoptotic fragmentation of DNA. Kinetics experiments revealed th at after 24 h a significant increase of DNA fragmentation already occu rred. Besides cadmium a second stimulus was identified to also cause a poptosis in this species, namely exposure to heat-treated Escherichia coli. In order to support the finding that both cadmium and E. coli in duce apoptosis in the sponge, expression of the apoptotic gene MA-3 wa s studied. The cDNA, SDMA3, was isolated and found io be 2247 nucleoti des long. The deduced amino acid sequence (M-r 50765) shares high simi larity with the corresponding mouse molecule. Like the mouse gene, the sponge MA-3 gene undergoes increased expression in response to apopto tic stimuli. While the specimens remained alive after treatment with c admium, the sponges treated with E. coli died after approximately 12 d . The E. coli-treated animals started to form gemmules 10 to 12 d afte r addition of the bacteria. Hence, the process of apoptosis in sponges is triggered by two different pathways, one which is initiated by exo genous factors, e.g. heavy metals. and a second one, caused by endogen ous factors, which leads to gemmule formation and a shift of the presu mably immortal cells to mortal cells. The latter assumption is support ed by the finding that during the process of bacteria-induced apoptosi s, which results in the death of the specimens, the activity of the te lomerase drops. It is concluded that the cells which appear to be immo rtal and telomerase-positive undergo apoptosis during the process of g emmule formation. In consequence cells not involved in the production of gemmules become mortal. Based on these data, it is proposed that ap optosis is a suitable biomarker in the bioindicator organism S. domunc ula to monitor unfavorable environmental conditions, at least in this animal phylum.