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

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

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

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

16. The DNA within cells is NOT naked!

17. Instead it is wrapped around histone proteins as chromatin

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

21. 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

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

23. MyoD is induced by treatments that induce mesoderm

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

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

30. How to Remember a Developmental Decision

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

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

33. Here’s the real thing

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

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

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