Résumé
The transmembrane 9 (TM9) family of proteins contains numerous members in
eukaryotes. Although their function remains essentially unknown in higher
eukaryotes, the Dictyostelium discoideum Phg1a TM9 protein was
recently reported to be essential for cellular adhesion and phagocytosis.
Herein, the function of Phg1a and of a new divergent member of the TM9 family
called Phg1b was further investigated in D. discoideum. The
phenotypes of PHG1a, PHG1b, and PHG1a/PHG1b double
knockout cells revealed that Phg1a and Phg1b proteins play a synergistic but
not redundant role in cellular adhesion, phagocytosis, growth, and
development. Complementation analysis supports a synergistic regulatory
function rather than a receptor role for Phg1a and Phg1b proteins. Together,
these results suggest that Phg1 proteins act as regulators of cellular
adhesion, possibly by controlling the intracellular transport in the endocytic
pathway and the composition of the cell surface.