Sponge aggregation factor: in situ localization by fluorescent monoclonal antibody techniques.

Area of Science:

• Cell Biology
• Marine Biology
• Biochemistry

Background:

• The aggregation factor (AF) from sponges facilitates heterophilic interactions between homologous cells.
• Previous studies identified a 47-kDa cell-binding protein within the AF complex using monoclonal antibody (mab) 5D2-D11.
• The 90 S AF particle is rarely observed in tissue sections of Geodia cydonium via electron microscopy.

Purpose of the Study:

• To localize the cell-binding domain of the aggregation factor (AF) in situ using fluorescent antibody techniques.
• To investigate the presence and state of the 47-kDa cell-binding protein within the sponge.
• To differentiate the cell-binding protein from other cell-matrix interaction components.

Main Methods:

• Fluorescent antibody technique utilizing monoclonal antibodies (mab 5D2-D11 and mab 7D5).
• Immuno-blotting technique to detect the presence of the cell-binding protein.
• Electron microscopy for visualizing AF particles (limited success).

Main Results:

• Monoclonal antibody 5D2-D11 strongly stained the plasma membranes of cells from various sponge regions.
• Monoclonal antibody 7D5 showed only weak reactivity with sponge surfaces.
• Immuno-blotting confirmed the cell-binding protein exists both associated with the AF complex and in a free state.
• The 47-kDa binding protein was not found in homologous glycoconjugates, lectins, or collagen.

Conclusions:

• The 47-kDa cell-binding protein, identified by mab 5D2-D11, is localized on the plasma membranes of sponge cells.
• This protein plays a crucial role in cell-cell adhesion mediated by the aggregation factor.
• The cell-binding protein is distinct from components involved in cell-matrix interactions.