In vitro aggregation of syncytia and cells of a Hexactinellida sponge.
Membrane recognition has been analyzed by studying the reaggregation of syncytia and cells dissociated from the tissues of the sponge Rhabdocalyptus dawsoni. Four obvious features are recognized. 1) There is true morphogenesis, led by the syncytia, which gives rise to compact, often very large (O.5 cm) aggregation bodies. Each body is a giant macrophagic syncytium surrounding groups of discrete undifferentiated cells. 2) Special coupling structures, the cytoplasmic perforate septa, establish communication between all body compartments, both syncytial and cellular. The whole aggregate can, therefore, be compared to one vast multinucleated cell. 3) During in vitro aggregation, membrane recognition processes permit different syncytia and cells to fuse, and internal compartmentalization is then achieved by the cytoplasmic septa. 4) Fragments of the flagellated choanosome, which is characteristic of sponges, are internalized by the syncytia. Following the collapse of the aggregate they degenerate. The survival of the body appears to depend on skeleton formation.
D000818:Animals; D002449:Cell Aggregation; D002450:Cell Communication; D002462:Cell Membrane / Q000648:ultrastructure; D002933:Cineradiography; D009024:Morphogenesis; D010587:Phagocytosis; D011161:Porifera / Q000166:cytology* / Q000648:ultrastructure