REGULATION OF GENE EXPRESSION

1. REGULATION OF GENE EXPRESSION

2. WHY REGULATE GENE EXPRESSION?? • Adaptation (Energy Conservation) • Development and differentiation

3. GENE EXPRESSION IN DIFFERENT CELLS Pancreatic cells Blood cells Muscle cell alpha cells beta cells WBCs RBCs

4. A PROKARYOTIC AND EUKARYOTIC CELL

5. REGULATION OF GENE EXPRESSION - PROKARYOTES

6. Structural Genes Promoter Gene 2 Gene 3 Gene 1 5’ 3’ AUG UAG UAA AUG UGA AUG Polycistronic mRNA THE OPERON Operon DNA Protein 1 Protein 2 Protein 3

7. REPRESSORS Regulatory gene mRNA Repressor RNA polymerase Operator Gene 2 Gene 3 Gene 1 Promoter 5’ 3’ No transcription No protein products

8. REGULATORY MECHANISMS INDUCTION Repressor is INACTIVATED through inducers to INITIATE / INDUCE transcription REPRESSION Repressor is ACTIVATED through corepressors to PREVENT / REPRESS transcription

9. Transcription Translation INDUCTION Active repressor No transcription, translation Inducer Inactive repressor

10. REPRESSION Inactive repressor Transcription Translation Corepressors Active repressor No transcription, translation

11. GENE REGULATION IN EUKARYOTES

12. Gene Regulation Can Take Place at Many Levels • Chromosome • Transcription • Processing of transcripts • Translation

13. GENE REGULATION AT THE CHROMOSOMAL LEVEL

14. Two Types of Chromatin • HETEROCHROMATIN Trancriptionally inactive tightly condensed • EUCHROMATIN Transcriptionally active Relatively relaxed

15. CHROMATIN STRUCTURE

16. Control region within nucleosome Control region outside nucleosome EFFECT OF CHROMATIN STRUCTURE ON TRANSCRIPTION GENE IS ACTIVE GENE IS INACTIVE

17. HAT Histone Acetylation

18. Histone Acetylation

19. DNA Methylation

21. X-Inactivation • Inactive X-Chromosome (Barr body) • Underacetylated at H4 • Hypermethylated

22. X-inactivation in humans • Red-green color blindness • Males = fully color blind • Females = mosaic retinas • Anhidrotic ectodermal dysplasia • Males = absence of teeth, lack of sweat glands • Females = random patterns of tissue with or without sweat glands

23. Arrangement of DNA

25. Antibody Diversity • Light chains: • Up to 300 Variable, 4 Joining and 1 Constant region • 300 x 4 = 1, 200 light chains • Heavy chains: • Up to 500 Variable, 4 Joining and 12 Diversity regions and 12 constant regions • 500 x 4 x 12 = 24, 000 light chains 1200 x 24,000 = 28,800,000 antibody molecules

26. REGULATION AT THE LEVEL OF TRANSCRIPTION

27. GTFs only produce a basal level of transcription i.e. very low • Gene-specific factors (activators) are further required to regulate the activity of gene expression

28. Enhancers/Silencers • Upstream or downstream • Close to the promoter or thousands of base pairs away • On either of the two strands of DNA • Act through intermediary or gene specific transcription factors proteins • Enhancers activate transcription • Silencers deactivate transcription

29. Enhancers/Silencers

30. Response Elements • Enhancers contain response elements that are responsive to certain metabolic factors • Cyclic AMP response element (CRE) • Glucocorticoid response element (GRE) • Heat shock element (HSE) • REs bind transcription factors produced under certain cell conditions to activate several related genes

31. cAMP Response Element (CRE) 5’- TGACGTCA -3’ 3’- ACTGCAGT -5’

32. CREB – the most important protein that you have never heard of • Implicated in • Cell proliferation • Cell differentiation • Spermatogenesis • Release of somatostatin (inhibitor growth hormone) • Development of T lymphocytes • Metabolism of the pineal gland • Adaptation to physical stress • Transcription of metabolic enzymes • Critical in learning and long term memory

33. Activation of CREB

34. Glucocorticoid Response Element

35. GENE REGULATION BY PROCESSING OF TRANSCRIPTS

36. Alternative Splicing

37. RNA EDITING

38. Regulation of Translation byPhosphorylation

39. mRNA Stability

40. Regulation of Transferrin Expression

41. Regulation of ferritin expression

42. RNA Interference …will be done with therapeutics

43. The End!