CELL AGGREGATION AND DIFFERENTIATION IN DICTYOSTELIUM

CELL AGGREGATION AND DIFFERENTIATION IN DICTYOSTELIUM

10.      CELL AGGREGATION AND DIFFERENTIATION IN DICTYOSTELIUM

Dictyostelium discoideum is a soil-living amoeba-like organism commonly known as slime mold. It consumes bacteria found in soil. Its life cycle begins as spore released from a mature fruiting body (sorocarp) and then this sorocarp the spore hatches under warm and moist conditions to give rise to Myxamoebae. Myxamoeba is the vegetative stage where they feed on bacteria but get together for aggregation during starvation. The life cycle of Dictyostelium is shown in the below figure.

10.1.      Mechanism of aggregation :

The molecular mechanism for the aggregation in Myxamoebae is dependent on the cAMP signalling. One cell that is termed as the founder of the colony, initially secrets the cAMP because of stress during starvation and the other cell respond this signal either by secreting more cAMP or by migrating towards the cAMP source cell. The cAMP molecule acts as a signal molecule for each cell in the following manner–

A GPCR-protein receptor is activated on cAMP reception

Receptor stimulates the Adenylate cyclase

cAMP diffuses out of the cell

Internal cAMP desensitizes the cAMP- GPCR receptor.

Another G-protein stimulates Phospholipase C

Calcium ion released by IP3 induction

Calcium ions rearrange the cytoskeleton to bear pseudopodia.

Because of receptor desensitization, cells show oscillatory behaviour and produces beautiful spirals seen in converging colonies. The aggregated amoebae work as pseudoplasmodium and known as the slug. This slug is having 100,000 cells and 2-4mm long body. The cAMP and DIF (differentiation inducing factor) are responsible for differentiation of slug into the prestalk and the prespore cells that switch the positions in the culmination stage and form the mature fruiting body (sorocarp).

The fruiting body stalk is formed by cells from the anterior end of the slug and the spores of the fruiting body are formed by the cells from the posterior end of the slug. After some hours the fruiting body has the ability to release mature spores, leads to Myxamoebae.


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