Abstract
BackgroundThe multicellular slug in Dictyostelium has a single tip that acts as an organising centre patterning the rest of the slug. High adenosine levels at the tip are believed to be responsible for this tip dominance and the adenosine antagonist, caffeine overrides this dominance promoting multiple tip formation.ResultsCaffeine induced multiple tip effect is conserved in all the Dictyostelids tested. Two key components of cAMP relay namely, cAMP phosphodiesterase (Pde4) and adenyl cyclase-A (AcaA) levels get reduced during secondary tip formation in Dictyostelium discoideum. Pharmacological inhibition of cAMP phosphodiesterase also resulted in multiple tips. Caffeine reduces cAMP levels by 16.4, 2.34, 4.71 and 6.30 folds, respectively in D. discoideum, D. aureostipes, D. minutum and Polysphondylium pallidum. We propose that altered cAMP levels, perturbed cAMP gradient and impaired signalling may be the critical factors for the origin of multiple tips in other Dictyostelids as well. In the presence of caffeine, slug cell movement gets impaired and restricted. The cell type specific markers, ecmA (prestalk) and pspA (prespore) cells are not equally contributing during additional tip formation. During additional tip emergence, prespore cells transdifferentiate to compensate the loss of prestalk cells.ConclusionCaffeine decreases adenyl cyclase–A (AcaA) levels and as a consequence low cAMP is synthesised altering the gradient. Further if cAMP phosphodiesterase (Pde4) levels go down in the presence of caffeine, the cAMP gradient breaks down. When there is no cAMP gradient, directional movement is inhibited and might favour re-differentiation of prespore to prestalk cells.
Highlights
The multicellular slug in Dictyostelium has a single tip that acts as an organising centre patterning the rest of the slug
Kinetics of multiple tip formation To examine the kinetics of multiple tip formation, we stained D. discoideum amobae with neutral red and allowed them to develop as slugs which were transferred to a non-nutrient plates containing 5 mM caffeine
We propose that reduced cAMP levels, suppression of tip dominance and altered cAMP gradient, together cause secondary tip formation in slugs
Summary
The multicellular slug in Dictyostelium has a single tip that acts as an organising centre patterning the rest of the slug. Cellular slime molds are unicellular, free living soil amoebae alternating its life cycle between growth and multicellular development [1]. As amoebae, they prey on bacteria and multiply until all the food is exhausted. At the onset of starvation, the amoebae secrete chemoattractants to communicate with each other enabling them to form a multicellular aggregate. The aggregates transform to a motile slug which later culminates to a fruiting body with a dead stalk holding a mass of dormant spores. D. discoideum slug consists of two prominent cell types: the anterior prestalk cells and the posterior prespore cells [2]. Four morphogenetic regulators viz., cAMP, adenosine, ammonia (NH3) and differentiation inducing factor (DIF) coordinate and regulate cell fate
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