Extracellular cyclic AMP during development of the cellular slime mold Polysphondylium violaceum: comparison of accumulation in the wild type and an aggregation-defective mutant

The polyketide synthase StlA is involved in inducing aggregation in Polysphondylium violaceum

In the social amoeba Dictyostelium discoideum, the polyketide MPBD (4-methyl-5-pentylbenzene-1,3-diol) regulates the gene expressions of cAMP signaling to make cells aggregation-competent and also induces spore maturation. The polyketide synthase StlA is responsible for MPBD biosynthesis in D. discoideum and appears to be conserved throughout the major groups of the social amoeba (Dictyostelia). In this study, we analyzed the function of StlA in Polysphondylium violaceum by identifying the gene sequence and creating the knockout mutants. We found that Pv-stlA- mutants had defects only in cell aggregation but not in spore maturation, indicating that the function of StlA in inducing spore maturation is species-specific. We also found that MPBD could rescue the aggregation defect in Pv-stlA- mutants whereas the mutants normally exhibited chemotaxis to their chemoattractant, glorin. Our data suggest that StlA is involved in inducing aggregation in P. violaceum by acting on signaling pathways other than chemotaxis in P. violaceum.

Signal transduction in Trypanosoma cruzi

Signal transduction plays a key role in regulating important functions in both multicellular and unicellular organisms and largely controls the manner in which cells respond to stimuli. Signal transduction pathways coordinate the functions in different type of cells in animals and control the growth and differentiation in unicellular organisms. Intracellular signal transduction pathways are largely activated by second messenger molecules. Trypanosoma cruzi has a complex life cycle involving four morphogenetic stages with various second messenger systems able to regulate its growth and differentiation. Signal transduction often alters the status of phosphorylation in target proteins and thus alters the activities of these proteins. In this review, two major signal transduction pathways, cyclic AMP-dependent pathway and mitogen-activated protein kinase pathway, are discussed. Protein phosphatases are also discussed due to their importance in dephosphorylating target proteins and terminating signal transduction. Understanding of the unique pathways in this pathogen may lead to the development of novel therapeutic agents.

An increase of cAMP-dependent protein kinase during development in Polysphondylium pallidum

Polysphondylium pallidum is a cellular slime mold in which, unlike in Dictyostelium discoideum, cAMP is not the chemotactic agent. The occurrence of a cAMP-dependent protein kinase in D. discoideum was demonstrated earlier and we suggested that it may mediate the intracellular effects of cAMP on the development of the organism, particularly since an increase in the amount of the enzyme during development was noted. In D. discoideum cAMP plays a dual role insofar as it serves both as chemotactic agent and as second messenger; it was of interest therefore, to determine whether a cAMP-dependent protein kinase occurred in P. pallidum. We found a cAMP-dependent protein kinase in P. pallidum using Kemptide as substrate. The regulatory subunit of the enzyme has an apparent molecular weight of 41,000 and seems to be similar in its properties with that isolated earlier from D. discoideum. The cAMP-dependent protein kinase catalytic subunits from the two species are also similar. Furthermore, there is a developmentally regulated, parallel, two- to threefold increase in the two subunits of the cAMP-dependent protein kinase in P. pallidum. The increase occurs before aggregates are formed. These findings are compatible with a role of the intracellular cAMP and of the cAMP-dependent protein kinase in the development of P. pallidum.