Ch II : Entry into M phase and MPF

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9 Terms

1
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meotic maturation and fertilisation of the xenopus egg

oogonia (2n cells) enter ore-meiotic S phase

  • oocyte grows to accumulate resources for fertilisation and oocyte I stops in G2/prophase I meiosis

progesterone released by neighbouring cells to oocyte I, resuming meiosis and enters reduction division 

  • GBVD germinal vesicular break down —> nuclear break down of oocyte 

  • oocyte asymmetric divises into 2 daughter cells

  • oocyte II arrested in metaphase II 

fertilisation of oocyte II will allow second meitoic divison 

<p>oogonia (2n cells) enter ore-meiotic S phase </p><ul><li><p>oocyte grows to accumulate resources for fertilisation and oocyte I stops in G2/prophase I meiosis</p></li></ul><p>progesterone released by neighbouring cells to oocyte I, resuming meiosis and enters reduction division&nbsp;</p><ul><li><p>GBVD germinal vesicular break down —&gt; nuclear break down of oocyte&nbsp;</p></li><li><p>oocyte asymmetric divises into 2 daughter cells</p></li><li><p>oocyte II arrested in metaphase II&nbsp;</p></li></ul><p>fertilisation of oocyte II will allow second meitoic divison&nbsp;</p><p></p>
2
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discovery of MPF by observing xenapus oocyte I and II

injection of cytoplasm from oocyte II (metaphase II) into oocyte I (prophase I) and inhibition of cycloheximide removed

  • oocyte I become oocyte II 

  • MPF maturation promoting factor active in oocyte II and enough to induce maturation of oocyte I 

<p>injection of cytoplasm from oocyte II (metaphase II) into oocyte I (prophase I) and inhibition of cycloheximide removed</p><ul><li><p>oocyte I become oocyte II&nbsp;</p></li><li><p>MPF maturation promoting factor active in oocyte II and enough to induce maturation of oocyte I&nbsp;</p></li></ul><p></p>
3
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discovery to determine if MPF universel (somatic cells)

injection of cytoplasm from somatic cell in Mitosis to xenopus oocyte

  • maturation of oocyte I to oocyte II

MPF = mitosis promoting factor —> universal

<p>injection of cytoplasm from somatic cell in Mitosis to xenopus oocyte </p><ul><li><p>maturation of oocyte I to oocyte II </p></li></ul><p>MPF = <strong>mitosis</strong> promoting factor —&gt; <strong>universal</strong> </p><p></p>
4
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xenopus model also reveals when MPF is active, so when is it active ?

MPF is rapidly activated at the end of G2/beginning of ad decreases rapidly at the end of telophase

<p>MPF is rapidly activated at the end of G2/beginning of ad decreases rapidly at the end of telophase </p>
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structure of an MPF 

MPF = CDK/Mitotic Cyclin complex

  • CDK1

  • cyclin B (mitotic cyclin)

however cyclin B is not sufficient for CDK1 activity 

  • phospho-substrate + ATP required 

  • CDK1 has 2 binding sites for these molecules 

<p>MPF = CDK/Mitotic Cyclin complex</p><ul><li><p>CDK1</p></li><li><p>cyclin B (mitotic cyclin)</p></li></ul><p>however cyclin B is not sufficient for CDK1 activity&nbsp;</p><ul><li><p>phospho-substrate + ATP required&nbsp;</p></li><li><p>CDK1 has 2 binding sites for these molecules&nbsp;</p></li></ul><p></p>
6
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what is MPF responsible for ?

  1. nuclear envelope breakdown

  2. spindle formation 

  3. disassembly of the nucleus 

  4. chromosomes condensation 

  5. actin remodelling

<ol><li><p>nuclear envelope breakdown</p></li><li><p>spindle formation&nbsp;</p></li><li><p>disassembly of the nucleus&nbsp;</p></li><li><p>chromosomes condensation&nbsp;</p></li><li><p>actin remodelling</p></li></ol><p></p>
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how does MPF play a role in chromosome condensation by phosphorylation of histone 3,1 and condensins

MPF controls phosphorylation :

A. condensins - bind to DNA and promote DNA coiling

B. Histones -

  • H1 → stabilises nucleosome structure, when phosphorylated its electrical charge changes and theres a reduction in DNA affinity (required for condensation

  • H3 → when phosphorylated it becomes an epigenetic mark that promotes recruitment of condensing factors

<p>MPF controls phosphorylation : </p><p>A. condensins - bind to DNA and promote DNA coiling</p><p>B. Histones -</p><ul><li><p>H1 → stabilises nucleosome structure, when phosphorylated its electrical charge changes and theres a reduction in DNA affinity (required for condensation</p></li><li><p>H3 → when phosphorylated it becomes an epigenetic mark that promotes recruitment of condensing factors </p></li></ul><p></p>
8
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what is role of MPF is the disappearance of the nuclear membrane during mitosis 

MPF phosphorylates Lamines (= supporting structure) and Lamine associated proteins (= junction between chromatin and inner nuclear membrane):

→ Lamine no longer interact w/ each other so dissociation of nuclear lamina and nuclear membrane fragments

→ physical association of chromatin w/ nuclear membrane by lamine is released and the chromatin is free to condensed 

<p>MPF <strong>phosphorylates</strong> <strong>Lamines</strong> (= supporting structure) and<strong> Lamine associated proteins</strong> (= junction between chromatin and inner nuclear membrane): </p><p>→ Lamine no longer interact w/ each other so <strong>dissociation</strong> of nuclear lamina and <strong>nuclear membrane</strong> <strong>fragments</strong> </p><p>→ physical association of chromatin w/ nuclear membrane by lamine is released and the <strong>chromatin is free</strong> to condensed&nbsp;</p>
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mechanism of nuclear membrane assembly

MPF inactive

  1. the nuclear membrane vesicles bind to chromosomes 

  2. vesicles fuse around the chromosomes to form envelope

  3. fusion of vesicles surrounding each chromosome

  4. chromsome de-condensation

<p>MPF inactive</p><ol><li><p>the nuclear membrane vesicles bind to chromosomes&nbsp;</p></li><li><p>vesicles fuse around the chromosomes to form envelope</p></li><li><p>fusion of vesicles surrounding each chromosome</p></li><li><p>chromsome de-condensation</p></li></ol><p></p>