2. If induction tells cells what to do How do they remember these instructions for a lifetime??

4. Cloning: The ultimate Transplant experiment Dolly

5. Cloning: The ultimate Transplant experiment Oops-- Here’s the real Dolly (guess which tissue she was cloned from!)

6. Cloning: The ultimate Transplant experiment

7. So HOW does cloning work?

8. Blastula stage cells Can be easily re-programmed

9. But cloning success drops dramatically as the age of the nuclear donor increases Gilbert Fig. 4.6

10. But cloning success drops dramatically as the age of the nuclear donor increases Gilbert Fig. 4.6 Why??

11. All cells have the same DNA and thus the same library of genes yet different mRNAs are made by different cells

13. Methylation is HERITABLE at the cell level and thus could be used by cells to remember decisions they have made ECB 3e 8-22

15. DNA imprinting: an example of how DNA methylation influences gene expression during development

16. Two maternal genomes: “normal” embryo, Poor development of Extraembryonic tissue Two paternal genomes: Very small embryo, “normal” development of Extraembryonic tissue

17. Imprinting results From pre-programmed Differences in DNA methylation Of selected genes in the sperm and egg

18. The DNA within cells is NOT naked!

19. Instead it is wrapped around histone proteins as chromatin

21. Post-translational modification of histones plays a key role in regulating gene expression

22. Post-translational modification of histones plays a key role in regulating gene expression

23. To understand a third mechanism of large scale gene regulation, let’s return to this experiment

24. If one transferred chromatin from a de-methylated fat cell that had become a myoblast it could tranform untreated fat cells. However frequency suggests Only one or a few of the genes have this ability

25. They ultimately identified a single gene- myoD - whose expression could convert,any other cell types into muscle cells

26. MyoD is induced by treatments that induce mesoderm

27. MyoD is expressed at the right place and time to be a master regulator of muscle development

29. But is this true???

30. Is myoD necessary for muscle formation? Oliver Smithies UNC Gene knockout Mario Capecchi Martin Evans Nobel prize in physiology and medicine 2007

33. MyoD works with related transcription factors to regulate the muscle cell fate

34. MyoD works with related transcription factors to regulate the muscle cell fate

35. I can tell you and even better story

36. How to Remember a Developmental Decision

37. Remember that Wingless is expressed by specific cells within each segment

38. Anterior Posterior Wg En Engrailed is expressed by cells posterior to those that express Wingless

39. Here’s the real thing

40. Engrailed expression initially requires Wingless signaling by the neighboring cells

41. Later, however, Engrailed becomes autoregulatory i.e., it turns on its own synthesis

42. In cells where engrailed is turned off, a set of special chromatin proteins bind to it and wrap it up in a permanently inactive state.

43. We also regulate stem cells And are mutated in cancer

44. We also regulate stem cells And are mutated in cancer