between the contributions of DdM7 and M10 to phagocytosis in these two cell
Studies of phagocytosis and adhesion in Dictyostelium have begun to uncover
adhesion receptors and proteins that link them to the underlying actin
cytoskeleton. Continued studies should result in the identification of links
between them but the initial results indicate that while the substrates engaged
by these receptors are specific to Dictyostelium, the same basic principles of
operation are at work in this lower eukaryote. The binding of food particles,
such as bacteria, stimulates the production of an actin-rich phagocytic cup.
Loss of key cytoskeletal proteins such as talin and M7 disables this pathway
and results in a severely reduced rate of phagocytosis. At least one receptor,
Phg1, is conserved throughout evolution and another, SadA, contains motifs
typical of mammalian adhesion receptors. Cell-cell contacts are essential for
early development and morphogenesis and one class is Ca 2+ -dependent and
shares some features with the cadherins of higher eukaryotes. Finally, FERM
proteins have been shown to play key roles in linking cell surface receptors to
the actin cytoskeleton in Dictysotelium as has been observed in mammalian
systems. This basic conservation of function throughout phylogeny suggests
that studies of Dictyosteium adhesion mutants with the same phenotypes will
expedite the process of characterizing the molecular details of these links
between adhesion receptors and the underlying actin cytoskeleton.
Work in the Titus laboratory is supported by a grant from the National
Institutes of Health as well as an Established Investigator Award from the
American Heart Association. The author thanks Dr Richard Tuxworth, Greg
Addicks, Stephen Stephens and Zach Ryan for their many contributions, past
and present, to the ongoing analysis of DdM7.
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