国外大学细胞生物学课件 英文课件25.ppt

D103 lecture 24 ? 2011 Grant MacGregor & Christine S ü tterlin – All rights reserved Page 1 D103 lecture 24 ? 2011 Grant MacGregor & Christine S ü tterlin – All rights reserved Page 2 Cytokinesis After telophase, a contractile ring of actin and myosinconstricts the equator ( cytokinesis ) and divides the cytoplasm to form two daughter cells. Cleavage furrow in a fertilized frog egg D103 lecture 24 ? 2011 Grant MacGregor & Christine S ü tterlin – All rights reserved Page 3 A contractile ring of actin and myosin II generates the force required for cytokinesis ? Actin - myosin II contractile ring is established in plane of metaphase plate . ? Myosin is kept inactive by phosphorylation by M-cyclin/CDK activity which is degraded prior to exit from anaphase .? Ring constricts via an acto-myosin contraction similar to that in muscle. ? The surface area of the two daughter cells is much greater than the original cell. To provide the additional membrane required, membrane vesicles are inserted adjacent to the leading edge of the cleavage furrow . Septins are a family of monomeric GTPases that are involved in this process. actin myosin II How does cell know where to locate contractile ring ? D103 lecture 24 ? 2011 Grant MacGregor & Christine S ü tterlin – All rights reserved Page 4 ? Actin - myosin II contractile ring is established at midbody where overlapping inter-polar MTsprovide signals for motor proteins to ponents of contractile ring . ? Activator (GEF) of Rho A is localized to midbody. ? Rho A coordinates activation of actin filamentformation and myosin IIactivation . ? Drosophila mutants lacking these proteins are unable plete cytokinesis . The midbody localizes molecules that stimulate Rho A activity to mediate formation of a contractile ring of actin and myosin II D103 lecture 24 ? 2011 Grant MacGregor & Christine S ü tterlin – All rights reserved Page 5 Meiosis - why bother ?