Loss of PakD affects cytoskeletal function in Dictyostelium discoideum development

Cell proliferation is important for an organism, especially during development. In mammals, many signal transduction pathways regulate cell proliferation; one of which involves protein kinase C (PKC) (1). However, many of the processes that occur between activation of PKC and the initiation of cell proliferation are not well defined. One of the processes that is crucial to cell proliferation is cytoskeletal regulation. In comparison to the complex mammalian cell, Dictyostelium discoideum is a simple model eukaryote which can be used to study many mammalian cell processes. D. discoideum normally exist as individual amoebae which hunt bacteria using chemotaxis towards folate. However, when the amoebae exhaust the resources in its environment and begin to starve, they will initiate multicellular development using chemotaxis towards cyclic-AMP (2). A search of the D. discoideum genome identified two PKC orthologs, thus making D. discoideum an excellent organism in which to study the role of PKC on cytoskeletal regulation.  We have been studying one of the PKC orthologs, PakD. Mutant cells either lacking or overexpressing the pakD gene were assayed for various cytoskeletal processes. We found that loss of PakD does have an observable effect on general cell shape.  In addition, loss of PakD inhibits chemotaxis towards cAMP without affecting chemotaxis towards folate. This suggests that the role of PakD is specific to development and not just required for general chemotaxis. Future work will include further characterization of the role of PakD using other cytoskeletal based assays.