1. Big lessons from little worms
Apoptosis
worm Image from Mingxue Cui

2. The worms are transparent

3. Worms are transparent
<1000 cells
One can follow the individual lineage of each of the cells

4. Deciphering the cell lineage of C. elegans

5. Deciphering the cell lineage of C. elegans

6. Cell death is also a “cell fate”

7. Specific cells are dying in a programmed manner
Programmed cell death
Specific cells are dying in a programmed manner

8. Programmed cell death (PCD)
The mechanism: apoptosis
Also associated with the fight of our body against cancer tumors
Is this an active process?

9. We know there is apoptosis
We know it is important in development and possibly in cancer
We don’t know whether it is an active process
We don’t know of any genes involved
Let alone, a pathway (if exists)
What do we do?

10. Forward Genetics: random mutations
Mutagenesis
Forward Genetics: random mutations

11. They found the guy who gets rid of the body
Next, they found the murderer

12. ced-3 acts to promote cell death

13. The gene is mapped and sequenced
Is it murder or suicide?
ced-3
ced-1
Mutant analysis
The gene is mapped and sequenced
Next step: does it have human homologes or is this just a worm-specific pathway?

14. Is it a worm-specific gene or do we have human homologs?

15. - The ced-3 gene encodes a protease, conserved in evolution
- It kills cells by degrading their proteins
Apoptosis is carried out by proteins.
It is an active process, not a passive death
Now we also know that human caspase is involved in apoptosis

16. A new mutation was isolated: ced-9
ced-9(-): ectopic cell death (cells that normally live, undergo apoptosis)

17. More and more mutants are isolated
Epistasis analysis and biochemical studies allow the scientists to build a pathway

18. Genetic control of programmed cell death
ced-9
ced-4
ced-3
Cell death
CED-4
CED-4 is inactive
CED-9
No death signal
Activates CED-3 caspase for the killing
CED-9
CED-4
Death signal

19. Gain of function mutations in bcl-2 were associated with human cancers (bcl= b cell lymphoma resulting from a translocation event)
Our body uses the same apoptotic mechanisms used in PCD, for killing “bad” cells
Identify mutants in worms (with the simplest assay) and find human homologs

20. Nobel Prize Lineage and programmed cell death
Physiology and Medicine 2002
Bob Horvitz
John Sulston
Sydney Brenner
Bob Horvitz

21. - Pro-apoptotic signals open up the channels, allowing cyt C to be released to the cytoplasm

22. A simplified representation of apoptosis
Proapoptotic
(BH3-only)
Noxa
Antiapoptotic
Bcl-2
Procaspase
Apaf
Proapoptotic
(multidomain)
Bax
Caspase
Cytochrome C
Mitochondria
All the regulators are from the same protein family (containing BH domains)