Reference:Developmental Biology - Scott. F Gilbert(9th edition)

1. CELL AGGREGATION AND
DIFFERENTIATION IN
DICTYOSTELIUM
KASHMEERA N.A.

2. DICTYOSTELIUM/CELLULAR SLIME MOULD/SOCIAL
AMOEBA/MYXAMOEBA
Solitary haploid amoeba.
Becomes multicellular when nutrition starvation occurs.

3. LIFE CYCLE – 3 STAGES
• AGGREGATION.
• MIGRATION.
• CULMINATION

4. 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.

5. • Each myxamoeba move towards c AMP for a
minute & release c AMP of their own.
• Movement is caused by change in cytoskeletal
polarity 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.

6. MIGRATION
• Cells pile atop another→tight aggregate
• Tip arises,bends →migrating
slug/grex/pseudoplasmodium.
• Grex with slimy sheath migrate from dark to
light.

7. • During migration, most prestalk cells are
anterior & → stalk.
• Prespore cells posterior →spore
• Some prestalk cells posterior→cup of sporesac
& basal disc of stalk.

8. CULMINATION
• Grex reach illuminated area→culmination
starts.
• 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.

9. 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.

10. Proteins and lipids impo. In final
differentiation.
• Lipid: DIF1(chlorinated lipid)
• Proteins: Trishanku, spore differentiation
factors(SDF1&2).

11. FINALLY…
• Stalk cells die
• Prespore cells→spore

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

13. DEVELOPMENTAL BIOLOGY – SCOTT
F. GILBERT 9th EDITION

14. THANK YOU