Your SlideShare is downloading. ×
  • Like
072412 high school teachers   2
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Now you can save presentations on your phone or tablet

Available for both IPhone and Android

Text the download link to your phone

Standard text messaging rates apply

072412 high school teachers 2

  • 193 views
Published

Day 2

Day 2

Published in Technology
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads

Views

Total Views
193
On SlideShare
0
From Embeds
0
Number of Embeds
0

Actions

Shares
Downloads
0
Comments
0
Likes
0

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide
  • Why do you need to arrest the cell cycle? (You don’t want to mate and do DNA replication simultaneously)
  • What a cell really wants to do is make more of itself. Therefore, there is a balance between mating (it is beneficial to be diploid) and cell cycle progression. If a cell is able to detect any molecules of alpha factor, then cells might experience an irreversible cell cycle arrest. Wild-type cells can eventually overcome the cell cycle arrest induced by the presence of alpha factor.Bar1 mutants will be hyper-sensitive to alpha-factor and will stay arrested in the presence of alpha-factor. (Since arrested cells don’t divide, they won’t grow up on a plate overnight)

Transcript

  • 1. Introduction to yeast genetics Michelle Attner July 24, 2012
  • 2. What is budding yeast, S. cerevisiae? Electron micrograph DIC (light microscopy)
  • 3. Advantages to budding yeast as a model organism• Simple, eukaryotic cell (~10μm diameter)• Compact genome (genome is sequenced)• Cells grow on plates and in culture• Short generation time (~90 minutes)• Live happily as haploids and diploids• Easy to manipulate genes (swap promoters, delete genes)• Easy to conduct genetic screens• Many yeast genes have evolutionarily conserved homologs in humans
  • 4. Outline and Learning Objectives: Intro to Yeast Genetics1. Understand the life cycle of budding yeast2. Describe how yeast cells mate, and understand how the BAR1 gene contributes to the regulation of this process3. Understand the mitotic cell cycle of budding yeast a. Explain how budding yeast was used as a model system to isolate genes required for cell cycle regulation b. Understand the basics of doing a genetic screen in yeast4. Understand the meiotic cell divisions of budding yeast a. Explain how sporulation and tetrad formation aids scientists studying yeast
  • 5. The life cycle of budding yeast An a and alphaYeast have 2 cell can fuse tomatings types: form ana and alpha a/alpha diploid. matinga haploids andalpha haploidsdivide a/alpha diploids can divide asexually or they can undergo meiosis to form four haploid gametes called spores Image: Wikipedia
  • 6. Brief genetics review• What is a gene?• What is an allele?• What is a mutation?• What is a genotype?• What is a phenotype?• What is the difference between mutations conferring recessive and dominant phenotypes? – Why is yeast great for studying mutations conferring recessive phenotypes? – How can you use yeast to determine if your mutation confers a recessive or dominant phenotype?
  • 7. Yeast mating is a fusion event 1. What is the signal for mating? • a cells secrete a factor • α cells secrete α factor • a cells have receptors for α factor, and vice versa 2. When α factor binds to receptors on a cell, a MAP kinase pathway is activated. 3. The output of this pathway is cell cycle arrest and shmoo formation 4. A shmoo is a mating projection that is necessary for cell fusion * Not shown in this diagram are nuclei, but they fuse too.Image: Wikipedia
  • 8. Light microscopy image of yeast shmoos
  • 9. Control of yeast mating by BAR1• The BAR1 gene is expressed in MATa cells• The Bar1 protein is a secreted protease that degrades α factor• Why might the cell have a mechanism for degrading α factor?• What do you predict would happen to bar1Δ mutants? (BAR1 gene is deleted)
  • 10. Outline and Learning Objectives: Intro to Yeast Genetics1. Understand the life cycle of budding yeast2. Describe how yeast cells mate, and understand how the BAR1 gene contributes to the regulation of this process3. Understand the mitotic cell cycle of budding yeast a. Explain how budding yeast was used as a model system to isolate genes required for cell cycle regulation b. Understand the basics of doing a genetic screen in yeast4. Understand the meiotic cell divisions of budding yeast a. Explain how sporulation and tetrad formation aids scientists studying yeast
  • 11. Overview of the cell cycleThe goal of mitosis is to producetwo daughter cells geneticallyidentical to the mother
  • 12. Zoom in on budding (vegetative growth) Phases of the cell cycle G1: Gap 1 S: DNA replication G2: Gap 2 M: Mitosis What happens during G1 and G2? Note that bud size gives you an indication of where the cell is in the cell cycle
  • 13. Imaging the cytoskeleton during the cell cycle in budding yeast Tubulin immunofluorence ofActin stained with phalloidin an anaphase cell Journal of Cell Biology
  • 14. How can we design a screen to find genes required for cell cycle progression?
  • 15. Designing a screen to find cell cycle genes1. Mutagenize yeast cells using a chemical that induces mutations in DNA2. What phenotype will we screen for?3. If these genes are essential for cell cycle progression, how will we pick mutants if they are all dead?4. How do we know which genes have the mutations?
  • 16. This screen was done!• Lee Hartwell and colleagues screened mutants for temperature-sensitive arrest in a cell cycle stage• For example, all cells with mutation 1 arrest as large- budded cells. Therefore, a wild-type copy of that gene is required for progression past the large-budded stage.• The scientists then figured out which genes the mutations were in. These genes were named cell division cycle or cdc• In this way, genes that control the different phases of the cell cycle were discovered.• Similar screen was done in another yeast species, S. pombe
  • 17. Outline and Learning Objectives: Intro to Yeast Genetics1. Understand the life cycle of budding yeast2. Describe how yeast cells mate, and understand how the BAR1 gene contributes to the regulation of this process3. Understand the mitotic cell cycle of budding yeast a. Explain how budding yeast was used as a model system to isolate genes required for cell cycle regulation b. Understand the basics of doing a genetic screen in yeast4. Understand the meiotic cell divisions of budding yeast a. Explain how sporulation and tetrad formation aids scientists studying yeast
  • 18. Budding yeast undergo meiosis to produce four haploid gametes in a process called sporulationStarvationinducessporulationin yeast In yeast, scientists can manipulate all four spores that are the products ofMarston et al., 2004 one diploid cell undergoing meiosis
  • 19. Using sporulation in genetic analysis of mutants• How can we ensure that our mutants have a mutation in only one gene?• What would happen if our mutant has a mutation in two genes?
  • 20. •••••••
  • 21. Conclusions• Today we discussed: – Life cycle of budding yeast: haploid, mating, diploid, sporulation – The basics of setting up a genetic screen• Questions?
  • 22. Acknowledgements• Mandana Sassanfar• Angelika Amon• Members of the Amon LabQuestions or comments:Michelle Attnermattner@mit.eduThanks!