MAP kinase in individual oocytes. MAP kinase 0.001 0.01 0.1 1 10 immunoblotting using progesterone (µM) a MAP-kinase-specific antibody. The first two lanes in each gel contain nonphosphorylated, –+ 0.03µM progesterone and phosphorylated, active MAP kinase (+). (From J.E. Ferrell, Jr., and 0.1 µM progesterone
E.M. Machleder, Science 280:895–898, 1998.
0.3 µM progesterone With permission from AAAS.)
Before you crushed the oocytes, you noticed that not all oocytes in individual dishes had white spots. Had some oocytes undergone partial activation and not yet reached the white-spot stage? To answer this question, you repeat the experiment, but this time you analyze MAP kinase activation in individual oocytes. You are surprised to find that each oocyte has either a fully activated or a completely inactive MAP kinase (Figure Q15–3B). How can an all-ornone response in individual oocytes give rise to a graded response in the population?
15–15 Propose specific types of mutations in the gene for the regulatory subunit of cyclic-AMP-dependent protein kinase (PKA) that could lead to either a permanently active PKA or a permanently inactive PKA.
15–16 Phosphorylase kinase integrates signals from the cyclic-AMP-dependent and Ca2+-dependent signaling pathways that control glycogen breakdown in liver and muscle cells (Figure Q15–4). Phosphorylase kinase is composed of four subunits. One is the protein kinase that catalyzes the addition of phosphate to glycogen phosphorylase to activate it for glycogen breakdown. The other three subunits are regulatory proteins that control the activity of the
Figure Q15–4 Integration of cyclic-AMP-dependent and Ca2+dependent signaling pathways by phosphorylase kinase in liver and muscle cells (Problem 15–16).
catalytic subunit. Two contain sites for phosphorylation by PKA, which is activated by cyclic AMP. The remaining subunit is calmodulin, which binds Ca2+ when the cytosolic Ca2+ concentration rises. The regulatory subunits control the equilibrium between the active and inactive conformations of the catalytic subunit, with each phosphate and Ca2+ nudging the equilibrium toward the active conformation. How does this arrangement allow phosphorylase kinase to serve its role as an integrator protein for the multiple pathways that stimulate glycogen breakdown?
15–17 The Wnt planar polarity signaling pathway normally ensures that each wing cell in Drosophila has a single hair. Overexpression of the Frizzled gene from a heat-shock promoter (hs-Fz) causes multiple hairs to grow from many cells (Figure Q15–5A). This phenotype is suppressed if hs-Fz is combined with a heterozygous deletion (DshΔ) of the Dishevelled gene (Figure Q15–5B). Do these results allow you to order the action of Frizzled and Dishevelled in the signaling pathway? If so, what is the order? Explain your reasoning.
Figure Q15–5 Pattern of hair growth on wing cells in genetically different Drosophila (Problem 15–17). (From C.G. Winter et al., Cell 105:81–91, 2001. With permission from Elsevier.)
Marks F, Klingmüller U & Müller-Decker K (2009) Cellular Signal Processing: An Introduction to the Molecular Mechanisms of Signal Transduction. New York: Garland Science.
Lim W, Mayer B & Pawson T (2015) Cell Signaling: Principles and Mechanisms. New York: Garland Science.
Principles of Cell Signaling