START or Restriction Point The Cell Cycle

The Main Jobs of the Cell Cycle: 1.To accurately transmit the genetic information! 2.To maintain normal ploidy; i.e. diploidy! Euploidy: additions of whole chromosome sets e.g. n, 2n, 3n, 4n = haploid, diploid, triploid, tetraploid Aneuploidy: additions or subtractions of one or more single chromosomes e.g. 2n + 1, 2n -1, 2n + 2, etc.

Properties Required for Transmission of Chromosomes During Cell Division 1. One and only one centromere 2. Functional telomere at both ends 3. Chromosomes must be linear (i.e. fully replicated) 4. Chromosomes cannot be too large or too small

S Phase of the Cell Cycle

Mitosis

Fibroblasts in Culture blue = DNA green = microtubules

Mitosis in an Early Fruit Fly Embryo

Anaphase in a plant cell

Metaphase in a mammalian cell

G1-S and G2-M are the major control points in the cell cycle Rao and Johnson cell fusion experiments 1.Fuse M phase cell with interphase cell: Interphase nucleus enters M 2.Fuse S phase cell with G1 cell: The G1 nucleus enters S phase 3.Fuse S phase cell with G2 cell: The G2 nucleus does not enter S phase

Cyclin Dependent Kinase Regulate the Cell Cycle

Experimental Systems Important for Cell Cycle Studies Arbacia punctulata Xenopus laevisSchizosaccharomyces pombe Saccharomyces cerevisiae

Fission yeast: Schizosaccharomyces pombe

Budding Yeast Saccharomyces cerevisiae

Isolating Temperature Sensitive Mutants in Haploid Yeast

Permissive (low) temperatureRestrictive (high) temperature Cdc Mutants Arrest at the Same Cell Cycle Phase

cdc mutant growing at permissive temp (23C) cdc mutant growth arrested after 6 hrs at non-permissive temp (36C) The Behavior of a Temperature Sensitive cdc Mutant

How to Clone cdc Genes in Yeast

Cdc Genes Encode Proteins Needed for DNA Replication Studies in S. cerevisiae

Cdc Genes Encode Proteins Needed for the G2-M Transition: Studies in S. pombe cdc2 + encodes a kinase Moreover = cdc28 in S. cerevisiae!

Cyclin was Discovered in Sea Urchin Embryos Protein Level Time cyclin A cyclin B MMM can stimulate to lay lots of eggs

Frog life cycle 1 mm sperm tadpole feeds, grows and bcecomes an adult frog OOCYTE GROWS WITHOUT DIVIDING (MONTHS) FERTILIZATION FERTILIZED EGG DIVIDES WITHOUT GROWING (HOURS)

The Maturation of Frog Eggs

An Assay for Maturation Promoting Factor (MPF) Yoshio Masui, 1971

MPF Activity Peaks Before Each Cell Division Moreover, MPF has kinase activity

Purification of MPF: The Birth of Cyclin Dependent Kinases This is cdc2 + !! (Cdc28 in S. cerevisiae) This is cyclin!! Which = cdc13 + in S. pombe

Phosphorylation of CDK Targets Changes Their Activity Now performs a cell cycle function

The Nobel Prize in Physiology or Medicine, 2001 “ for their discovery of key regulators of the cell cycle ”