The cDNA for the full-length lectin from the marine sponge Geodia cydonium was cloned. Analysis of the deduced aa sequence revealed that this lectin belongs to the group of galectins. The full-length galectin, which was obtained also in a recombinant form, has an M(r) of 20,877; in the processed form it is a 15 kDa polypeptide. The enriched aggregation factor from G.cydonium also was determined to contain, besides minimal amounts of the galectin, a 140 kDa polypeptide which is involved in cell-cell adhesion. Monoclonal antibodies have been raised against this protein; Fab' fragments prepared from them abolished cell-cell reaggregation. Cell reaggregation experiments revealed that the aggregation factor is an essential component in the aggregation process but it requires likewise the presence of the galectin. Antibodies against the galectin blocked the aggregation factor-mediated cell adhesion. A plasma membrane component was identified (a 29 kDa polypeptide) which interacted with the aggregation factor in the presence of galectin; binding could be blocked both by antibodies against the galectin as well as against the aggregation factor. Immunohistochemical analysis revealed that spherulous cells contain the galectin but not the aggregation factor. By laser scanning microscopy, it is shown that both the aggregation factor and the galectin are located at the rim of the cells. From these data we conclude that the G.cydonium aggregation factor binds to the cells via a galectin bridge.

The b~omarker concept lnvolves the use of biochemical, cellular and phys~ological parameters a s screening tools In environmental surveillance Stress protelns, such as heat shock protelns (HSPs), fulflll many of the requirements for belng Ideal candidates In a b~o m a r k e r strategy for envlronmental monitonny Sponges (Porifera) are one of the major phyla tound in the m a n n e hard-substrate benthos, both w~t h respect to the number of s p e c~e s and b~o m a % s However, only recently have genes from sponges been cloned Here w e describe the ~solatlon of the cDNA encodlng a heat shock protein of M, (relative molecular welght) 70 kDa (HSP70) The cDNA H5P70 from the marlne sponge C e o d~a cj~donlum has a length of 2 3 kb and encodes an AA sequrnce of M, 72 579 The sponge HSP70 dlsplays characterlstlc features of the HSP70 famlly The HSP70 proteln 1s Induced by natural stressors ~ncludlng changes In tempelature as well as pH, as demonstrated by Western blot analysls No response was observed after treating the samples with hypotonic or hypertonlc conditions Our results p r o v~d e the first molecular evldence that HSP7O of sponges 1s a useful blomarker

No abstract