Cell-cell adhesion in Dictyostelium discoideum.

Area of Science:

• Developmental Biology
• Cell Biology
• Molecular Biology

Background:

• Cell-cell adhesion is crucial for multicellular organism development.
• Dictyostelium discoideum serves as a model organism for studying early multicellular development and cell adhesion.

Purpose of the Study:

• To elucidate the distinct molecular mechanisms and temporal regulation of cell-cell adhesion during Dictyostelium discoideum development.
• To identify the specific molecules involved in mediating these adhesion events.

Main Methods:

• Antibody-mediated blocking of cell adhesion.
• Identification and characterization of cell surface glycoproteins (gp24, gp80).
• Molecular cloning and genetic analysis using cDNA and genomic libraries, including Southern analysis.
• Isolation and characterization of mutant strains lacking specific adhesion molecules.

Main Results:

• Three distinct, sequentially expressed cell-cell adhesion mechanisms were identified.
• Glycoprotein 24 (gp24) mediates early adhesion, while glycoprotein 80 (gp80) mediates EDTA-resistant adhesion during aggregation.
• A third, later adhesion mechanism, insensitive to antibodies against gp24 and gp80, was observed.
• The gene for gp24 was found to exist in two tandem copies, potentially explaining the difficulty in generating null mutants.

Conclusions:

• The sequential appearance of distinct adhesion molecules (gp24, gp80, and a third unknown factor) orchestrates the transition from single cells to a multicellular organism in Dictyostelium.
• Genetic analysis revealed mutations affecting gp80 accumulation, highlighting its role and the redundancy of adhesion mechanisms.
• This stepwise mechanism ensures successful multicellular development from solitary cells.