Life as a worm-- the nematode C. elegans

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? http://www.polleverywhere.com/multiple_choice_polls/3fUwSIjK4zkVqsC

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. 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 germlineand the gut both arise from single founder cells

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

19. 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 (the parmutants) 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

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

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

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

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

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

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

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

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

35. 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. 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

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

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 vulva cannot form The “bag of worms” phenotype