Seasonal localization of a collagenous protein in the organic matrix of spicules from the gorgonian Leptogorgia virgulata (Cnidaria: Gorgonacea)

Spicules of the gorgonian Leptogorgia virgulata possess an insoluble matrix fraction that is predominantly collagenous in summer months. This collagenous component is largely absent in winter months. Using an antibody directed against the 140 kD collagenous protein (CP) of the insoluble matrix, immuno-gold labelling was employed to localized this protein at the transmission electron-microscopy level throughout the year, and in different areas of the gorgonian colonies. Within the tip regions, the 140 kD CP varied throughout the year in the spicules, electron-dense bodies (EDBs) of scleroblasts, polyp vesicles, desmocytes and axes. In the mid and base regions, the 140 kD CP varied throughout the year in the spicules, EDBs and lysosomes of scleroblasts, desmocytes and axes. This variation in the location and density of the label suggests a dynamic annual cycling of the collagenous component of the insoluble matrix. EDBs may transport a collagenous component of the matrix to the spicule-forming vacuole. A component of the 140 kD CP may be transported and/or degraded by polyp vesicles and lysosomes, respectively. The pattern of labelling of the axial region suggests that translocation and storage of a component of the collagenous protein may occur. Environmental factors may be responsible for the triggering of matrix cycling.