A putative receptor mediating cell-density sensing in Dictyostelium.

Area of Science:

• Cellular and Molecular Biology
• Developmental Biology
• Biochemistry

Background:

• Starved Dictyostelium discoideum cells secrete conditioned medium factor (CMF) to communicate cell density.
• CMF triggers gene expression and aggregation via cAMP signaling, involving distinct G protein-dependent and independent pathways.
• Understanding the receptors for CMF is crucial for elucidating cell density sensing mechanisms.

Purpose of the Study:

• To identify and characterize the receptor(s) responsible for sensing conditioned medium factor (CMF) in Dictyostelium.
• To investigate the role of identified receptors in CMF-mediated G protein-independent gene expression and G protein-dependent signaling.

Main Methods:

• Affinity chromatography using CMF-Sepharose to isolate CMF-binding proteins.
• Protein identification via partial amino acid sequencing and cDNA isolation.
• Functional characterization through expression in insect cells and gene disruption in Dictyostelium.

Main Results:

• A novel 50-kDa membrane protein, conditioned medium factor receptor 1 (CMFR1), was identified as a CMF-binding protein.
• CMFR1 exhibits no significant homology to known proteins and possesses predicted transmembrane domains.
• Disruption of CMFR1 in Dictyostelium led to reduced CMF binding and abolished CMF-induced G protein-independent gene expression, while G protein-dependent pathways remained functional.

Conclusions:

• CMFR1 is a key receptor mediating cell density sensing through conditioned medium factor (CMF).
• CMFR1 is specifically involved in the G protein-independent pathway of CMF-induced gene expression.
• Dictyostelium likely utilizes multiple receptors to sense CMF, with CMFR1 playing a distinct role in density-dependent responses.