2. 2

3. Life as a worm-- the nematode C. elegans

4. This humble animal:
Revealed how cell lineage controls cell fate

5. This humble animal:
Revealed how cell lineage controls cell fate
Revealed the proteins in the RTK pathway,
one of the “big Five”

6. This humble animal:
Revealed how cell lineage controls cell fate
Revealed the proteins in the RTK pathway,
one of the “big Five”
3. Taught us about programmed cell death,
key to neural development and
mis-regulated in cancer

7. This humble animal:
Revealed how cell lineage controls cell fate
Revealed the proteins in the RTK pathway,
one of the “big Five”
3. Taught us about programmed cell death,
key to neural development and
mis-regulated in cancer
Gave us insights that led to the discovery of
both RNAi and microRNAs

8. This humble animal:
Revealed how cell lineage controls cell fate
Revealed the proteins in the RTK pathway,
one of the “big Five”
3. Taught us about programmed cell death,
key to neural development and
mis-regulated in cancer
Gave us insights that led to the discovery of
both RNAi and microRNAs
5. Helped us understand organogenesis
at the single cell level

9. Life as a worm-- the nematode C. elegans

10. Fertilized egg to adult in ~2.5 days

11. Think like a geneticist! If you have a single heterozygous mutant
fly or worm, how many generations
till you have a homozygous mutant animal?

12. Hermaphrodites do it by themselves

13. An entire C. elegans hermaphrodite worm consists of exactly 959 cells
EVERY SINGLE TIME,
allowing one to follow the lineage
of every cell in the body.
Males have exactly 1,032 cells every single time!

14. Here’s how it works

15. Let’s look a bit more closely
Was that too fast?
Let’s look a bit more closely

16. Cell lineage: family trees, cellular style

17. Most lineages do not consist of single tissue types
but the germline and the gut
both arise from single founder cells

18. Most lineages do not consist of single tissue types
but the germline and the gut
both arise from single founder cells

19. the secret of embryonic development
Within this lineage is
the secret of embryonic development

20. Even cell death is programmed into the lineage.
C. elegans was used to identify
the machinery that regulates
programmed cell death (apoptosis)
in ALL animals

21. The Nobel Prize in Physiology or Medicine 2002
"for their discoveries concerning ’
genetic regulation of organ development
and programmed cell death'"
Sidney Brenner
H. Robert Horvitz
John Sulston

22. How can lineage control cell fate?
One mechanism is through
asymmetric segregation of “determinants”
Determinants = mRNAs or proteins
That drive cell fate decisions

23. Remember the P granules and how they are segregated into a
single cell at
each cell division?
This cell is P4,
The progenitor of the
germline
P granules
DNA
Gilbert 8.33

24. Scientists then looked for mutatns in which P granules are found in
(the par mutants)
in which P granules are found in
ALL daughter cells
wildtype
par-3 mutant

25. We now know the Par proteins are key to making
epithelial cells polarized
in all animals
Apical
Basal
Apical- towards the lumen
Basal- towards underlying cells
Lateral- contacting other epithelial cells 25

27. X New Biology career option: Worm genealogist
But first you must learn to
read a cell lineage diagram
embryo
1st stage larva
2nd stage larva
Increasing age of worm X

28. How do we read a cell lineage diagram?
embryo
1st stage larva
2nd stage larva
Increasing age of worm X
What do you think is
going on
here?

29. How do we read a cell lineage diagram? Branching = cell division
embryo
1st stage larva
2nd stage larva
Increasing age of worm X
What do you think is
going on
here?
Branching = cell division

30. How do we read a cell lineage diagram?
embryo
1st stage larva
2nd stage larva
Increasing age of worm X
What do you think is
going on
here?

31. How do we read a cell lineage diagram? X = programmed cell death
embryo
1st stage larva
2nd stage larva
Increasing age of worm X
What do you think is going on here?
X = programmed cell death

32. How do we read a cell lineage diagram?
embryo
1st stage larva
2nd stage larva
Increasing age of worm X
How about here?

33. X How do we read a cell lineage diagram? How about here?
embryo
1st stage larva
2nd stage larva
Increasing age of worm X
How about here?
line ending = cell differentiation

34. Brenner and his colleagues found that
mutations can alter lineages in many ways

35. Changes in the pattern of cell division
Example #1- lin-22
Changes in the pattern of cell division

36. Example #1- lin-22 Changes in the pattern of cell division
lin-22 is the worm version of the Drosophila
pair-rule transcription factor hairy

37. Changes in the timing of cell division
Example #2- lin-14
Changes in the timing of cell division L1 L2 L1 L2 L1 L1 L1

38. Scientists studying regulation of lin-14
were the first to identify functions for microRNAs

39. And the heterochronic regulator lin-28 can be part of
the recipe for making “induced pluripotent stem cells”

40. The nematode also provides a great model for organogenesis:
e.g., Building the vulva
Vulva

41. Vulva Formation in C. elegans: A model for organogenesis
One inducing cell
Three receiving cells
22 cells
One complete organ 41

43. The key players One gonadal anchor cell (AC)
6 vulval precursor cells (VPCs)
1° vulval precursor cell
2° vulval precursor cell
3° vulval precursor cell 43

44. Cell ablation helped define the key players

45. Cell ablation helped define the key players
What can we conclude from these experiments?

46. The anchor cell (AC) signals to the vulval precursor cells (VPCs), telling them to adopt vulval fates
Hypodermis
(normal skin)
Hypodermis
(normal skin)
Vulva

47. All cells are created equal
Any of the VPCs can adopt 1° and 2° fates to form a vulva

48. Scientists also isolated “vulvaless mutants” because without signaling from the anchor cell, all cells adopt a 3° fate

49. Without signaling from the anchor cell, all cells adopt a 3° fate
What happens in this scenario?

50. Without signaling from the anchor cell, a The “bag of worms” phenotype
vulva cannot form
The “bag of worms” phenotype

51. Mutational analysis also revealed that there are
two steps involved in forming a vulva
Step 1: Anchor cell signal reaches central 3 Vulval precursor cells (VPCs)
Step 2: Central cell sends inhibitory signal to neighbors

52. What happens if the inhibitory signal from the
1° VPC is blocked?

53. What happens if the inhibitory signal from the 1° VPC is blocked?
All three central VPCs adopt 1° VPC fate
And three partial vulvas form!

54. What are the actual signals involved
in vulva formation?
Step 1: Anchor cell signal reaches central 3 Vulval precursor cells (VPCs)
Anchor cell
1°/2° VPC

55. The vul mutations helped define the RTK-Ras pathway,
which is mutationally activated
in more than half of all human tumors

56. This pathway’s so important in Cancer it got 2 spots on this Table!
Here’s Notch

57. Ras plays a central role in signal transduction downstream of receptor tyrosine kinases (RTKs)

58. Oncogenic Ras mutations are stuck in the ON state
Ras plays a central role in signal transduction downstream of receptor tyrosine kinases (RTKs)
Oncogenic Ras mutations are stuck in the ON state

59. What are the actual signals involved
in vulva formation?
Step 2: Central cell sends inhibitory signal to neighbors

60. Does this remind you of anything we learned earlier?

61. Remember me?

62. lin-12 is the
transmembrane
receptor that receives the
lateral inhibition signal
and it is the
C. Elegans homolog
of Notch