CELL AGGREGATION AND DIFFERENTIATION IN

DICTYOSTELIUM

KASHMEERA N.A.

DICTYOSTELIUM/CELLULAR SLIME MOULD/SOCIAL AMOEBA/MYXAMOEBA

Solitary haploid amoeba.Becomes multicellular when nutrition starvation occurs.

LIFE CYCLE – 3 STAGES

• AGGREGATION.

• MIGRATION.

• CULMINATION

AGGREGATION.

• Nutrient starvation → myxamoeba express cAMP

• Tens of thousands of myxamoebae join together to form moving streams of cells that converge at a central point.

• Each myxamoeba move towards c AMP for a minute & release c AMP of their own.

• Movement is caused by change in cytoskeletalpolarity brought about by c AMP.

• After movement cell unresponsive for about 4 minutes.

• This time, phosphodiesterase in ECM cleave c AMP in environment & make receptors free to receive another c AMP pulse.

• C AMP pulse arrives as spiral waves,cell move one step towards center.

MIGRATION

• Cells pile atop another→tight aggregate

• Tip arises,bends →migrating slug/grex/pseudoplasmodium.

• Grex with slimy sheath migrate from dark to light.

• During migration, most prestalk cells are anterior & → stalk.

• Prespore cells posterior →spore

• Some prestalk cells posterior→cup of sporesac& basal disc of stalk.

CULMINATION

• Grex reach illuminated area→culminationstarts.

• Grex differentiate→frutingbody & stalk.

• Fate of each cell depend on stage of cell cycle they were in while starvation.

• Cell in S&early G2 → ↑Ca2+ →stalk

• Mid/late G2 →↓Ca2+ →spore.

Response to c AMP

• Diff. in prespore & prestalk cells.

• Prespore: c AMP→β catenin→enter nucleus & express spore specific mRNA.

• Prestalk(anterior): c AMP suppress this pathway & become stalk.

Proteins and lipids impo. In final differentiation.

• Lipid: DIF1(chlorinated lipid)

• Proteins: Trishanku, spore differentiation factors(SDF1&2).

FINALLY…

• Stalk cells die

• Prespore cells→spore

ALTRUISM IN DICTYOSTELIUM

• Prestalk cells act as altruists which die for dispersion of kin cells - the prestalk cells.

DEVELOPMENTAL BIOLOGY – SCOTT F. GILBERT 9th EDITION

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