Species-specific aggregation factor in sponges. VI. Aggregation receptor from the cell surface.

Area of Science:

• Marine biology
• Cellular adhesion mechanisms
• Biochemistry of sponge aggregation

Background:

• Cell-cell adhesion is vital for multicellular organisms.
• Sponge aggregation provides a model system to study adhesion mechanisms.
• Understanding aggregation receptors is key to deciphering cell-surface interactions.

Purpose of the Study:

• To isolate and characterize the aggregation receptor from Geodia cydonium.
• To elucidate the role of this receptor in the cell aggregation process.
• To investigate the binding characteristics and regulation of the aggregation receptor.

Main Methods:

• Purification of the aggregation receptor using ultracentrifugation and gel filtration.
• Chemical analysis to determine the composition of the receptor.
• Functional assays involving cell depletion and re-charging with receptor molecules.
• Competition experiments to study receptor binding dynamics.

Main Results:

• The aggregation receptor was purified, showing high carbohydrate content (81%) and some protein (7.5%).
• Receptor activity is sensitive to Na-periodate; it's released by Ca2+ removal or trypsin treatment.
• Cells depleted of the receptor can be re-bound with isolated molecules, requiring physiological salt and Ca2+.
• The receptor mediates secondary aggregation initiated by a soluble factor and is newly synthesized during aggregation.

Conclusions:

• The isolated receptor is essential for secondary aggregation in Geodia cydonium.
• Its binding is regulated by Ca2+ and cell surface proteases.
• Soluble receptor molecules can inhibit secondary aggregation through competition.
• Sponge cells synthesize new aggregation receptors during the aggregation process.