Lecture 4
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Questions and Answers

What is the significance of exponential growth in embryonic development?

  • It is irrelevant to embryonic development
  • It slows down the process of cleavage division
  • It generates a large number of cells (correct)
  • It only occurs in the later stages of development

    • What is the primary function of cleavage division?

  • To generate a large number of cells from a single fertilized zygote (correct)
  • To distribute the zygotic genome unevenly among cells
  • To halt embryonic development
  • To generate a small number of specialized cells

    • What is the significance of each cleavage cell having a copy of the zygotic genome?

  • It restricts their ability to differentiate
  • It allows each cell to express a subset of the genome (correct)
  • It is unnecessary for embryonic development
  • It prevents further cell division

    • What is the outcome of ordinary mitotic division during cleavage?

    <p>Genetically equal cells</p> Signup and view all the answers

    What is the analogy used to describe the process of cleavage?

    <p>Building a house using a single big boulder of stone</p> Signup and view all the answers

    What is the significance of embryonic cells being able to move relative to their position?

    <p>It is essential for building specific structures</p> Signup and view all the answers

    What is the term for the cells resulting from cleavage division?

    <p>Blastomeres</p> Signup and view all the answers

    What is the purpose of generating many copies of the zygotic genome during cleavage?

    <p>To allow each cell to express a subset of the genome</p> Signup and view all the answers

    What is the process that phosphorylates target proteins inside the blastomere or cleavage cells?

    <p>Kinase</p> Signup and view all the answers

    What type of proteins are phosphorylated by the Cyclin B-CDC2 complex?

    <p>Histone proteins</p> Signup and view all the answers

    What is the source of MPF in the early embryo?

    <p>Maternal RNAs</p> Signup and view all the answers

    What is the result of the depletion of maternally-loaded Cyclin B and other cell cycle factors?

    <p>Zygotic genome activation</p> Signup and view all the answers

    What is the characteristic of the late embryonic cell cycle?

    <p>Asynchronous and slow</p> Signup and view all the answers

    What is the result of the transition from maternal to zygotic genome transcription?

    <p>All of the above</p> Signup and view all the answers

    What is the role of the Cyclin B-CDC2 complex in mitosis?

    <p>To phosphorylate target proteins</p> Signup and view all the answers

    What is the consequence of the degradation of the nuclear membrane?

    <p>Breakdown of the nuclear membrane</p> Signup and view all the answers

    What is the significance of the transition from maternal to zygotic genome transcription?

    <p>It leads to the loss of synchronous division</p> Signup and view all the answers

    What is the role of the regulators of Cyclin B in the early embryo?

    <p>They reside in the cytoplasm of the egg</p> Signup and view all the answers

    What is the primary function of maternal cytoplasmic factors in an oocyte?

    <p>To segregate cytoplasmic components into different blastomeres</p> Signup and view all the answers

    What is the result of an unequal distribution of cytoplasmic components in the progeny of cells?

    <p>Different combinations of cytoplasmic components in the progeny of cells</p> Signup and view all the answers

    What is the significance of the ratio of nuclear volume to cytoplasmic volume during cell division?

    <p>It is a universal aspect of cell division</p> Signup and view all the answers

    What is the role of MPF (mitosis promoting factor) in the transition from the zygote stage to the cleavage stage?

    <p>To fuel the transition from the zygote stage to the cleavage stage</p> Signup and view all the answers

    What are the two subunits of MPF?

    <p>Cyclin B and cdc2</p> Signup and view all the answers

    What is the fate of MPF during mitosis?

    <p>It is degraded during mitosis</p> Signup and view all the answers

    What happens to Cyclin B during mitosis?

    <p>It is degraded during mitosis</p> Signup and view all the answers

    What is the consequence of Cyclin B breakdown during mitosis?

    <p>MPF is inactivated</p> Signup and view all the answers

    What is the result of the re-synthesis of Cyclin B during the S phase?

    <p>MPF is activated</p> Signup and view all the answers

    What is the significance of the set point of nuclear volume to cytoplasmic volume ratio?

    <p>It is species-specific</p> Signup and view all the answers

    What type of cell cycle is characterized by the absence of gap phases and a biphasic pattern?

    <p>Cell cycle of early cleavage divisions</p> Signup and view all the answers

    Which factor promotes the transition from G2 to M phase in normal cell cycles?

    <p>Cyclin-cdc2 complex</p> Signup and view all the answers

    What is the characteristic of the first cleavage furrow in early cleavage divisions?

    <p>It occurs in a plane perpendicular to the axis of the mitotic spindle</p> Signup and view all the answers

    Which type of egg is characterized by a dense amount of yolk concentrated at one pole?

    <p>Telolecithal</p> Signup and view all the answers

    What is the characteristic of holoblastic radial cleavage in amphibians?

    <p>It is complete and involves the whole oocyte</p> Signup and view all the answers

    What is the role of maternal gene products in cleavage pattern?

    <p>They determine the orientation of the mitotic spindle</p> Signup and view all the answers

    Which type of cleavage is characteristic of birds, reptiles, and fish?

    <p>Meroblastic discoidal cleavage</p> Signup and view all the answers

    What is the effect of yolk on cleavage divisions in slightly telolecithal eggs?

    <p>It slows down the cleavage divisions</p> Signup and view all the answers

    What is the characteristic of the third plane of cleavage in amphibians?

    <p>It is horizontal and cuts the oocyte more displaced towards the animal pole</p> Signup and view all the answers

    Which type of cleavage is characteristic of insects?

    <p>Meroblastic superficial cleavage</p> Signup and view all the answers

    What is the primary function of the cells that form outside the blastocyst during embryonic development?

    <p>To form the trophectoderm and facilitate implantation</p> Signup and view all the answers

    What is the characteristic of the cleavage process in avian embryos?

    <p>Stack of cell layers with a subgerminal cavity</p> Signup and view all the answers

    What is the significance of the pluripotency gene markers in the inner cell mass (ICM)?

    <p>They indicate the presence of pluripotent stem cells</p> Signup and view all the answers

    What is the outcome of the 4th plane of cleavage in avian embryos?

    <p>Formation of centrally located and peripherally located cells</p> Signup and view all the answers

    What is the term for the cells that form the hypoblast layer in avian embryos?

    <p>Hypoblast</p> Signup and view all the answers

    What is the characteristic of the area pellucida in avian embryos?

    <p>It appears light or translucent under the microscope</p> Signup and view all the answers

    What is the significance of regulative development in embryonic cells?

    <p>It enables the development of embryonic cells based on cell-cell interaction</p> Signup and view all the answers

    What is the characteristic of the end of cleavage in mammalian embryos?

    <p>Formation of 2 distinct cell populations</p> Signup and view all the answers

    What is the characteristic of the cleavage division in the animal hemisphere?

    <p>It cleaves the animal hemisphere faster</p> Signup and view all the answers

    What is the term for the smaller blastomeres at the top portion of the embryo?

    <p>Micromeres</p> Signup and view all the answers

    What is the significance of the gray crescent in a fertilized oocyte?

    <p>It is a sign of fertilization</p> Signup and view all the answers

    What is the stage of embryonic development at which the internal cavity called blastocoel is formed?

    <p>Blastula stage</p> Signup and view all the answers

    What is the characteristic of the cleavage in mammalian cleavage?

    <p>It is holoblastic and rotational</p> Signup and view all the answers

    What is the significance of the slow cleavage in mammals?

    <p>It is an evolutionary adaptation to secure the embryo in the uterus</p> Signup and view all the answers

    What is the event that occurs at the 8-cell stage in mammalian cleavage?

    <p>Compaction</p> Signup and view all the answers

    What is the result of polarization at the 16-cell stage in mammalian cleavage?

    <p>The formation of the inner cell mass</p> Signup and view all the answers

    What is the term for the formation of the blastocoel in mammalian cleavage?

    <p>Cavitation</p> Signup and view all the answers

    What is the characteristic of the cell division in mammalian cleavage?

    <p>It is asynchronous and slow</p> Signup and view all the answers

    Study Notes

    Cleavage to Blastulation

    Functions of Cleavage Division

    • Generates a large number of cells:
      • From a single fertilized zygote to a multicellular embryonic phase
      • Embryonic cells capable of moving relative to each other
      • Analogy: breaking a large boulder into smaller stones to build a house
    • Generates many copies of the zygotic genome:
      • Each cell in the cleaving embryo has its own copy of the zygotic genome
      • Cell division is ordinary mitotic division, making all cells genetically equal
      • Each cell has the freedom to express its own subset of the genome, guiding its developmental pathway
    • Segregates cytoplasmic components into different blastomeres:
      • Maternal cytoplasmic factors (preformed guidelines) are distributed into different cells
      • In an oocyte, these components are in the form of maternal mRNAs (silenced) ready to be translated into proteins once activated by fertilization

    MPF (Mitosis Promoting Factor)

    • Translator of maternal mRNAs, fuelling the transition from the zygote phase to the cleavage phase
    • Composed of two subunits: Cyclin B and cdc2 (cyclin-dependent kinase 1)
    • MPF is periodically active, used by mitosis, and gets degraded, then re-synthesized to fuel mitosis

    Cycling of Cells

    • Synthesis and degradation of Cyclin B
    • Activation and deactivation of cdc2 kinases
    • The cyclin B-cdc2 complex is active, phosphorylating target proteins inside the blastomere or cleavage cells

    Source of MPF in the Early Embryo

    • Cyclin B is translated from maternal RNAs
    • All necessary components for cell cycling are also maternally derived

    Depletion of Maternally-Loaded Cyclin B and Other Cell Cycle Factors

    • Zygotic transcription must begin, marking the transition from maternal to zygotic genome transcription
    • New phenomena occur: addition of gap phases, loss of synchronous division, transcription of new mRNAs, and synthesis of different regulators

    Cell Cycle Control

    • MPF controls the cell cycle
    • In a typical somatic cell, the cell cycle includes M, S, G1, and G2 phases
    • In early cleavage divisions, there are no gap phases, and the cell cycle is biphasic (M and S phases)

    Factors Influencing Cleavage Pattern

    • Maternal cytoplasmic factors
    • Amount and distribution of yolk
    • Types of egg yolk content: isolecithal, mesolecithal, telolecithal, and centrolecithal

    Patterns of Cleavage and Cleavage Symmetry

    • Holoblastic (complete) cleavage: isolecithal and mesolecithal oocytes
    • Meroblastic (incomplete) cleavage: telolecithal oocytes
    • Cleavage patterns: radial, rotational, spiral, and bilateral

    Cleavage to Blastula

    • Amphibian cleavage: holoblastic radial, with three distinct regions recognized
    • Mammalian cleavage: holoblastic rotational, slow, and asynchronous, with a transient window of time for formation of an odd-numbered cell
    • Avian cleavage: involves only the blastodisc, with a subgerminal cavity forming, and eventually, the epiblast and hypoblast

    Developmental Properties of Cleaving Embryos

    • Regulative development: development of embryonic cells based on cell-cell interaction
    • Totipotent: embryonic cells have the ability to develop into any cell type

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    Description

    Learn about the process of cleavage division, its functions, and how it leads to the next phase of development in fertilized oocytes.

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