1 / 55

Shmoo Al Capp (1948) – Li’l Abner

Shmoo Al Capp (1948) – Li’l Abner. Marsh and Rose diagram. The next two lectures, and beyond. Genetics and epigenetics – examples (distinction, similarities, overlap) The power of the evolutionary perspective A brief preview – mutations A brief preview – genetic screen

kura
Download Presentation

Shmoo Al Capp (1948) – Li’l Abner

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Shmoo Al Capp (1948) – Li’l Abner

  2. Marsh and Rose diagram

  3. The next two lectures, and beyond • Genetics and epigenetics – examples (distinction, similarities, overlap) • The power of the evolutionary perspective • A brief preview – mutations • A brief preview – genetic screen • A brief preview – suppressor genetics • Today – yeast, flies, humans. Wednesday – plants. Thursday night (7 pm onwards) – review session for midterm.

  4. Amazing but true A wild-type haploid yeast cell contains THREE copies of mating type-determining genes: • Copy #1: the a1 and a2 genes (silent). • Copy #2: the a1 and a2 genes (also silent). • Copy #3: An additional copy of genes in item 1, or of the genes in item 2, but active. Whichever genes are contained in copy #3 determines the mating type.

  5. In an a strain, the genetic information at MAT and at HMLais identical. • The one at MAT is expressed, but the one at HML is not – it is epigenetically silenced. a2 a1 a2 a1 a2 a1 a cell HMLa MAT HMRa cen silent active silent

  6. A note on homework • Good job – I am impressed, and pleasantly surprised, both with the number of responses, and the quality of the writing. • Many gave the correct answer – two mating types evolved to prevent X from happening. No one, however, gave a complete answer: why is X bad? In other words, why did yeast evolve to protect themselves against X happening? What would happen to yeast if X were to happen frequently?

  7. Loss of silencing at the silent mating type cassettes creates a “nonmater” – a haploid that is a/a and that thinks it’s a diploid. a2 a1 a2 a1 a2 a1 a cell HMLa MAT HMRa cen active active active

  8. Screen for silencing mutants A sample “screen”: • Take haploid cells. • Mutate them. • Screen for those that don’t mate. Problem: mating is so much more than proper silencing of mating type loci!!

  9. The mating pheromone response Also see Fig. A.13. Thorner diagram Jeremy Thorner

  10. How to screen for silencing mutants a2 a1 a2 a1 a2 a1 a cell HMLa MAT HMRa cen silent active silent Jasper Rine and Ira Herskowitz (1987) Genetics 116: 9-22.

  11. How to screen for silencing mutants a2 a1 a2 a1 a2 a1 HMLa mata1-1 HMLa cen silent active silent Note: mata1-1 is a special allele of the a gene – it is recessive to a Jasper Rine and Ira Herskowitz (1987) Genetics 116: 9-22.

  12. Rine schematic mate to a cells Jasper Rine and Ira Herskowitz (1987) Genetics 116: 9-22.

  13. The data • Colonies screened: 675,000 • Colonies that mated to a: 295 • Major complementation groups: 4 silent information regulators: SIR1, SIR2, SIR3, SIR4 Jasper Rine and Ira Herskowitz (1987) Genetics 116: 9-22.

  14. Compaction into chromatin brings the eukaryotic genome to life 15,000x compaction < 10-5 metres > 1 metre

  15. “Beads on a string”?

  16. The Nucleosome Core Particle:8 histones, 146 bp of DNA

  17. Histones: Conserved and Charged H.s. = Lycopersicon esculentum

  18. “Extremely conserved histone H4 N terminus is dispensable for growth but essential for repressing the silent mating loci in yeast” (M. Grunstein) Fig. 3 kayne Deletion of histone tail led to no obvious effect, except the yeast stopped mating. Why? Loss of silencing at the mating type loci! Kayne et al. (1988) Cell 55: 27-39.

  19. Acetylation of lysine in histone tail neutralizes its charge (1964) Covalent modification of histones as a regulatory mechanism?

  20. “Genetic evidence for an interaction between SIR3 and histone H4 in the repression of the silent mating loci in Saccharomyces cerevisiae” Reverse genetics: introduce point mutations in H4 tail!! Johnson et al. (1990) PNAS 87: 6286-6290.

  21. Table 2 Johnson et al. (1990) PNAS 87: 6286-6290.

  22. And 5 years later … Sir3p and Sir4p bind H3 and H4 tails Hecht et al. (1995) Cell 80: 583.

  23. The key question How do the SIRs spread over the mating type loci genes? = how do the SIRs actually silence txn?

  24. Roy Frye (Pitt) “Characterization of five human cDNAs with homology to the yeast SIR2 gene: Sir2-like proteins (sirtuins) metabolize NAD and may have protein ADP-ribosyltransferase activity” BBRC 260: 273 (1999). 1. Bacteria have proteins homologous to Sir2. 2. So do humans (>5). 3. The bacterial proteins are enzymes, and use NAD to ADP-ribosylate other proteins.

  25. J. Denu: Sir2p is a NAD-dependenthistone deacetylase (HDAC) Sir2p Tanner et al., PNAS 97: 14178 (2000)

  26. Rusche L, Kirchmaier A, Rine J (2002) Mol. Biol. Cell 13: 2207.

  27. The unique power of an evolutionary perspective on biology Caloric restriction  longevity Why? • Lin, S. J., Defossez, P. A. & Guarente, L. Requirement of NAD and SIR2 for life-span extension by calorie restriction in Saccharomyces cerevisiae. Science289, 2126−2128 (2000) • Howitz KT, … Sinclair DA. Small molecule activators of sirtuins extend Saccharomyces cerevisiae lifespan. Nature. 2003 Sep 11;425(6954):191-6.  resveratrol • Baur et al (2006). Resveratrol improves health and survival of mice on a high-calorie diet. Nature. 444(7117):337-42 • Lagouge et al. (2006) Resveratrol improves mitochondrial function and protects against metabolic disease by activating SIRT1 and PGC-1alpha. Cell. 2006 Dec 15;127(6):1109-22.

  28. Baur et al. Nature 444: 337. Lagouge et al. Cell 127: 1109.

  29. Hermann Joseph Muller 1946 Nobel Prize in Medicine: "for the discovery of the production of mutations by means of X-ray irradiation"

  30. Genetic screen: • Su(var)2-5 • Su(var)3-9 13.13

  31. Su(var)3-9 = heterochromatin protein 1 (HP1)

  32. Who would have thunk it? NCBI: Su(var)3-9 contains a domain (the SET domain) that is somewhat similar to, ahem, RUBISCO methyltransferase. Su(var)3-9 is a HISTONE methyltransferase.

  33. Histone methylation

  34. Calling David Duchovny and Gillian Anderson • Su(var)3-9 was given this name because it was the 9th gene isolated on the 3rd chromosome in a screen for Su(var)s. • It methylates lysine 9 in histone H3. This was discovered 18 years after it was named.

  35. And finally • HP1 preferentially BINDS histone H3 methylated on lysine 9. • That’s why Su(var)3-9 determines localization of HP1 to heterochromatin (it methylates histones in heterochromatin).

  36. HP1 HP1

  37. HP1 HP1 HP1 HP1 HP1 HP1 HP1 HP1 = = =

  38. Homology(orthologs of heterochomatin proteins in fission yeast, insects, and humans)

  39. Analogy Fission yeast, flies, mammals. Budding yeast.

  40. From egg to embryo ?

  41. Homeotic mutations (W. Bateson) Genetics Allele Heterozygous Homozygous “… Not that there has merely been a change, but that something has been changed into the likeness of something else.”

  42. antennapedia wt

More Related