Sponge cell culture: A comparative evaluation of adhesion to a native tissue extract and other culture substrates

Hexactinellids are deep water sponges that possess syncytial rather than cellular tissues. In order to investigate the syncytial character of the tissue of these unusual sponges, primary cultures were developed using a substrate of acellular tissue extract (ATE) that promotes the adhesion and spreading of sponge tissues. Primary cultures of the hexactinellid sponge Rhabdocalyptus dawsoni, grown on this substrate, form thinly spread, multinucleate, confluent tissue masses which exhibit active cytoplasmic streaming. Sponge tissue adhered equally well to commercial substrates of concanavalin A and poly-l-lysine, but did not adhere to chicken collagen. Acellular tissue extracts prepared from demosponges, which are known to be cellular, also promoted adhesion and spreading of cells from those sponges. Scanning electron microscopy showed adherent Rhabdocalyptus tissue to have an uninterrupted, smooth membrane covering the entire culture, unlike primary cultures of the cellular demosponge, Haliclona sp., which consisted of numerous individual cells. Tissue from freshly collected sponges adhered preferentially to ATE from a conspecific. However, after continued wounding, tissue adhered indescriminately to any substrate. The tissue extract congealed if added to sea water or 10 mM CaCl2, forming a white, cloudy solid, which could be fixed and sectioned for transmission electron microscopy. Thin sections of the congealed extract showed it to contain membranes but no visible collagen fibrils.