Size Control in Fission Yeast
In fission yeast, where growth governs progression through G2/M, a wee1 mutation causes entry into mitosis at an abnormally small size, resulting in a shorter G2. G1 is lengthened, suggesting that progression through Start (beginning of cell cycle) is responsive to growth when the G2/M control is lost. Furthermore, cells in poor nutrient conditions grow slowly and therefore take longer to double in size and divide. Low nutrient levels also reset the growth threshold so that cell progresses through the cell cycle at a smaller size. Finally, wee1 mutant fission yeast cells are smaller than wild-type cells, but take just as long to go through the cell cycle. This is possible because small yeast cells grow slower, that is, their added total mass per unit time is smaller than that of normal cells.
A spatial gradient is thought to coordinate cell size and mitotic entry in fission yeast. The Pom1 protein kinase (green) is localized to the cell cortex, with the highest concentration at the cell tips. The cell-cycle regulators Cdr2, Cdr1 and Wee1 are present in cortical nodes in the middle of the cell (blue and red dots). a, In small cells, the Pom1 gradient reaches most of the cortical nodes (blue dots). Pom1 inhibits Cdr2, preventing Cdr2 and Cdr1 from inhibiting Wee1, and allowing Wee1 to phosphorylate Cdk1, thus inactivating cyclin-dependent kinase (CDK) activity and preventing entry into mitosis. b, In long cells, the Pom1 gradient does not reach the cortical nodes (red dots), and therefore Cdr2 and Cdr1 remain active in the nodes. Cdr2 and Cdr1 inhibit Wee1, preventing phosphorylation of Cdk1 and thereby leading to activation of CDK and mitotic entry. (This simplified diagram omits several other regulators of CDK activity.)
Read more about this topic: Schizosaccharomyces Pombe
Famous quotes containing the words size, control, fission and/or yeast:
“Great causes are never tried on their merits; but the cause is reduced to particulars to suit the size of the partizans, and the contention is ever hottest on minor matters.”
—Ralph Waldo Emerson (1803–1882)
“... the black girls didn’t get these pills because their black ministers were up on the pulpit saying that birth control pills were black genocide. What I’m saying is that black men have exploited black women.... They didn’t want them to have any choice about their reproductive health. And if you can’t control your reproduction, you can’t control your life.”
—Joycelyn Elders (b. 1933)
“The pace of science forces the pace of technique. Theoretical physics forces atomic energy on us; the successful production of the fission bomb forces upon us the manufacture of the hydrogen bomb. We do not choose our problems, we do not choose our products; we are pushed, we are forced—by what? By a system which has no purpose and goal transcending it, and which makes man its appendix.”
—Erich Fromm (1900–1980)
“Blues is to jazz what yeast is to bread—without it, it’s flat.”
—Carmen McRae (b. 1922)