MAP Kinases in Meiosis

which the substrate kinase is converted to its active A recent meeting in Spain discussed the most important form will vary as the square of the activity of the upcell divisions in your life: the meioses that produced the stream kinase. Combining two such steps in succession egg and sperm that fused to create you. Most of the produces a cascade in which the activity of MAP kinase talks at the meeting (“Signal Transduction Pathways and varies as the fourth power of the activity of the MAPKKK Checkpoint Controls in Meiotic Maturation,” Cuenca, so that a 2.5-fold increase in the activity of MAPKKK September 4–7, 1997) focused on the cell cycle that changes the activity of MAP kinase from 10% to 90% produces oocytes and finally eggs from the germ line of its maximal value. By experimentally manipulating cells of female animals. This meiotic cycle is regulated the level of c-Mos (the MAPKKK that controls oocyte differently from the mitotic cycles of somatic cells. Nonmaturation) added to oocyte extracts, Ferrell showed proliferating somatic cells exit the cell cycle in G1, that the activation of MAP kinase does indeed switch whereas oocytes arrest in G2 and can escape from this from off to on in response to small increases in the pause up to 50 years later. In their fully grown but G2amount of added Mos, with a Hill coefficient (a measure arrested state, the oocytes are immature and require a of cooperativity) of almost 5. physiological stimulus to undergo maturation: the entry Strong as this cooperativity is (the Hill coefficient for into the meiotic divisions that converts them into unfertilthe binding of oxygen to hemoglobin is 2.8), individual ized eggs. The stimuli for maturation vary (steroid horoocytes show an even more switch-like response to the mones in vertebrates, modified purines in starfish, and maturation-inducing stimulus of progesterone. Ferrell