Drosophila Oogenesis and Fertilization
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Drosophila Oogenesis and Fertilization

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What is the role of nurse cells during Drosophila oogenesis?

  • They directly fertilize the oocyte.
  • They provide nutrients to the oocyte post-fertilization.
  • They synthesize maternal proteins and mRNAs for storage. (correct)
  • They aid in fertilization.

    • What happens to nurse cells at the end of oogenesis?

  • They migrate to the oviduct.
  • They fuse with the oocyte.
  • They continue to proliferate.
  • They undergo apoptosis. (correct)

    • How do Drosophila oocytes remain until ovulation?

  • They are actively dividing.
  • They begin fertilization.
  • They complete meiosis.
  • They are paused at metaphase I. (correct)

    • What prevents polyspermy during fertilization in Drosophila?

    <p>Single entry site for sperm.</p> Signup and view all the answers

    What is a unique feature of sperm entry into the Drosophila egg?

    <p>The sperm enters intact without fusion.</p> Signup and view all the answers

    What initiates the resumption of meiosis in Drosophila oocytes upon entering the oviduct?

    <p>Mechanical pressure that opens Ca2+ channels.</p> Signup and view all the answers

    Where is the sperm entry site located on the Drosophila egg?

    <p>At the future dorsal anterior region.</p> Signup and view all the answers

    What occurs to the egg before the sperm enters during Drosophila fertilization?

    <p>It is activated and has begun body axes specification.</p> Signup and view all the answers

    What is the role of the acrosome reaction during fertilization in Drosophila?

    <p>It enables the sperm to break down the egg's plasma membrane.</p> Signup and view all the answers

    During which cleavage cycle do pole cells begin to form in Drosophila embryos?

    <p>Cycle 9</p> Signup and view all the answers

    What characterizes the division during cycle 14 of Drosophila embryogenesis?

    <p>Cell divisions are asynchronous with varying durations.</p> Signup and view all the answers

    What marks the transition from maternal to zygotic control in Drosophila?

    <p>Degradation of maternal mRNAs and proteins.</p> Signup and view all the answers

    What happens to the cell membrane after division 13 in Drosophila cleavage?

    <p>It folds inward to partition the energids into cells.</p> Signup and view all the answers

    What is an energid in the context of Drosophila cleavage?

    <p>A nucleus surrounded by actin filaments and microtubules.</p> Signup and view all the answers

    What is the primary type of cleavage exhibited by Drosophila until cycle 13?

    <p>Superficial meroblastic cleavage.</p> Signup and view all the answers

    What inhibits the formation of the cellular blastoderm in Drosophila?

    <p>Inhibiting microtubules.</p> Signup and view all the answers

    What is the first large-scale movement that occurs during gastrulation?

    <p>Ventral furrow formation</p> Signup and view all the answers

    Which cells flank the ventral midline during gastrulation?

    <p>Surface ectoderm cells</p> Signup and view all the answers

    What phase follows the mid-blastula transition?

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

    What is the significance of the germ band during development?

    <p>It includes all cells destined to form the trunk of the embryo.</p> Signup and view all the answers

    Where are cells destined to become posterior larval structures located?

    <p>Behind the head</p> Signup and view all the answers

    Which event occurs after the germ band has extended?

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

    What condition needs to be met before hatching occurs?

    <p>The germ band must retract.</p> Signup and view all the answers

    How does the general body plan of Drosophila change from embryo to adult?

    <p>It maintains the same body plan.</p> Signup and view all the answers

    What is the primary role of nurse cells during Drosophila oogenesis?

    <p>To provide nutrients to the developing oocyte</p> Signup and view all the answers

    Which life stage follows the larval phase in Drosophila development?

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

    What process occurs during the metamorphosis of Drosophila?

    <p>Remodeling of the body and generation of adult structures</p> Signup and view all the answers

    How many life stages does Drosophila undergo?

    <p>4</p> Signup and view all the answers

    What defines the anterior-posterior axis in Drosophila development?

    <p>The positioning of head and tail regions</p> Signup and view all the answers

    How does the oocyte in Drosophila develop from stem cells?

    <p>Through incomplete division leading to connected cells</p> Signup and view all the answers

    Which process occurs during the early stages of Drosophila embryogenesis?

    <p>Syncytial cleavage</p> Signup and view all the answers

    What distinguishes the germarium in Drosophila ovaries?

    <p>It is the most apical structure housing stem cells.</p> Signup and view all the answers

    Which type of genes is primarily regulated by gap genes in Drosophila development?

    <p>Pair-rule genes</p> Signup and view all the answers

    What is the role of bicoid mRNA in Drosophila embryogenesis?

    <p>Specifies anterior structures</p> Signup and view all the answers

    What does nanos mRNA specify in Drosophila development?

    <p>Posterior structures</p> Signup and view all the answers

    How are bicoid and nanos mRNAs anchored in the oocyte?

    <p>By proteins binding their 3' UTRs</p> Signup and view all the answers

    What does the protein product of the gurken mRNA influence in Drosophila?

    <p>Posteriorization of follicle cells</p> Signup and view all the answers

    Which of the following proteins is recruited to the posterior edge of the oocyte cytoplasm?

    <p>WPar-1 protein</p> Signup and view all the answers

    What is the initial function of Par-1 in the oocyte?

    <p>Organizing microtubules</p> Signup and view all the answers

    Which organelle primarily produces gurken mRNA in Drosophila?

    <p>Nurse cells</p> Signup and view all the answers

    What is the primary function of segment polarity gene mutants in Drosophila embryos?

    <p>To show defects in segment structures</p> Signup and view all the answers

    When is the expression of segmentation genes established in Drosophila embryos?

    <p>Before gastrulation</p> Signup and view all the answers

    Which pair-rule gene is mentioned as being expressed in seven stripes in Drosophila?

    <p>Fushi tarazu (ftz)</p> Signup and view all the answers

    Which segments make up the thoracic regions in Drosophila?

    <p>T1, T2, T3</p> Signup and view all the answers

    What defines the relationship between segments and parasegments in Drosophila?

    <p>Segments and parasegments are out of phase by one compartment</p> Signup and view all the answers

    What is true about the compartments of a segment in Drosophila?

    <p>Segments have both anterior and posterior compartments</p> Signup and view all the answers

    What is the assumed correspondence between pair-rule gene expression and later embryonic structures?

    <p>There is no correspondence between them</p> Signup and view all the answers

    Which of the following describes the structure of parasegments in Drosophila?

    <p>Each parasegment includes the posterior compartment of one segment and the anterior compartment of the next</p> Signup and view all the answers

    Study Notes

    Drosophila Development

    • Textbook: Chapter 10, pages 303-310, 312-330
    • Chapter Overview: Drosophila fertilization, cleavage, anterior-posterior axis establishment, and dorsal-ventral axis establishment

    Drosophila

    • Classification: Phylum - arthropod, Class - insecta, Protostome
    • Model Organism: Thomas Hunt Morgan introduced the fruit fly as a model organism in the early 1900s.
    • Genome/Mutations: Complete genome sequence known, easy mutant generation

    Drosophila Lifecycle

    • Stages: Embryo, larva, pupa, adult
    • Embryogenesis: Syncytial cleavage until 13th cell division, cellularization, gastrulation/segmentation, organogenesis
    • Larva: Embryo hatches as a larva, 3 instars (separate by molts)
    • Pupa: Larvae pupate at end of 3rd instar, remodeling for adult structures (metamorphosis)
    • Adult: 9-10 days after fertilization, adult fly emerges

    Drosophila Oogenesis

    • Ovaries: Pair, 15-20 ovarioles/egg tubes
    • Egg Chambers/Arrangement: Arranged linearly, least mature near germarium, mature furthest
    • Germarium: Apical structure, stem cell location
    • Egg Chambers: Clusters of cells surrounded by follicular cell, Each chamber produces one mature egg
    • Oogenesis Stages: Stem cell divides incompletely (no cytoplasmic cleavage) 4 times, generating 16 cells connected by cytoplasmic bridges. 15 of these cells form nurse cells; 1 cell becomes the oocyte. Oocyte matures as the egg chamber moves away from the germarium.
    • Nurse Cells: Synthesize maternal proteins and mRNAs stored in oocyte, undergo apoptosis at end of oogenesis.
    • Mature Oocyte: Released into oviduct, surrounded by follicular cells, paused at metaphase I until ovulation.

    Drosophila Fertilization

    • Different Activation: Sperm enters an egg already activated.
    • Ca2+ channels: Open when oocytes enter the oviduct due to mechanical pressure. Ca2+ initiates meiosis and translation of maternal mRNAs.
    • Single Entry Site: Only one site (micropyle) for sperm entry, prevents polyspermy (multiple sperm). No cortical granules.

    Drosophila Cleavage

    • Superficial Meroblastic: Nuclei divide without cytokinesis (karyokinesis) until cycle 13.
    • Syncytial Stage: Nuclei divide in the center until cycle 8.
    • Posterior Pole Cells: ~5 nuclei reach posterior pole by cycle 9, form pole cells and create membranes that turn into gametes.
    • Cycle 10: Nuclei migrate to periphery, mitosis continues at a slower rate.
    • Energids: Each nucleus + actin filaments and cytoplasmic islands
    • Division 13: Cell membrane folds inward, creating individual cells. The cellular blastoderm forms after 3 hrs. This process can be blocked by inhibiting microtubules, and the cellular blastoderm forms 3 hrs. post fertilization.
    • Mid-blastula Transition: Cycle 14, asynchronous divisions; maternal proteins/mRNAs breakdown, zygotic transcription begins

    Gastrulation

    • Rapid Cell Movement: Begins shortly after the mid-blastula transition.
    • Ventral Furrow: Prospective mesoderm cells (~1,000) fold inward to create ventral furrow, initiating gastrulation.
    • Furrow Closure: Furrow closes at the top to form a closed ventral tube.
    • Ectoderm/Cephalic Furrow: Ectoderm bends to form the cephalic furrow
    • Pole Cells: Internalize at the posterior end.

    Gastrulation Cont'd

    • Germ Band: Collection of cells along the ventral midline forming the trunk of the embryo, extends posteriorly and wraps around the dorsal surface.
    • Posterior Embryo Structures: More posterior structures are located behind the head during germ band extension.

    Drosophila Body Plan

    • Repeating Units: Embryo, larva, and adult have the same body plan (head, tail, repeating segments).
    • Segments: Thorax (3 segments), abdomen (8 segments)
    • Identity: Each segment has its own identity.

    Genetic Mechanisms Patterning the Drosophila Body

    • Forward Genetic Approach: Identifies genes by introducing mutations to examine mutant phenotypes and identifying associated genes
    • Nobel Prize (1995): Work by Edward Lewis, Christiane Nüsslein-Volhard, and Eric Wieschaus

    Hierarchy of Genes

    • Maternal Effect Genes: Code for transcription factors, translational regulators (morphogens)
    • Gap Genes: The first zygotic genes to be expressed, regulated by maternal effect genes.
    • Pair-rule genes: Regulated by gap genes, expression at segment boundaries.
    • Segment Polarity Genes: Regulated by pair-rule genes, expression in specific regions of each segment.
    • Homeotic Selector Genes: Regulated by other genes; specify segment identity.

    Maternal Gradients

    • AP Axis: Determined by two maternal mRNAs: bicoid and nanos,
    • Bicoid: Specifies anterior structures (head, mouth, thorax)
    • Nanos: Specifies posterior structures
    • Tethered mRNAs: Bicoid at anterior, nanos at posterior; bound via protein to 3’UTR.

    Hunchback and Caudal

    • Maternal mRNAs: Hunchback and caudal are other critical maternal mRNAs for anterior-posterior patterning.
    • Even Distribution: Distributed evenly across the oocyte.
    • Post-fertilization Translation: Translated after fertilization to form gradients.
    • High Levels: High levels of hunchback at anterior, high levels of caudal at posterior.
    • Translation Regulation: Bicoid and Nanos regulate translation of specific mRNAs

    How Bicoid Produces Anterior Structures

    • Repression of Caudal Translation: Bicoid represses translation of caudal mRNA, creating a region without caudal or inducing structures to the posterior.
    • Transcription Factor Action: Bicoid acts as a transcription factor, activating the expression of target genes in the anterior embryo.
    • Maternal and Zygotic Sources: Hunchback protein in early embryos originate from maternal and zygotic mRNAs.

    Terminal Gene Group

    • Acron and Telson: These structures (acron-head, telson-tail) form terminal portion, generated via maternal mRNAs tailless and huckebein proteins spread through cytoplasm, affecting terminal region development. Bicoid presence affects acron formation, while its lack leads to telson formation.
    • Maternal mRNA Diffusion: Tailless and huckebein proteins diffuse, influencing terminal region development
    • • Bicoid Influence: Bicoid presence leads to acron formation, its absence to telson formation.

    Summary of AP Axis Formation

    • Three Gene Sets: AP axis is defined by three sets of genes specifying anterior, posterior, and terminal regions.
    • Key Gene Groups: Bicoid/Hunchback, Nanos and Caudal, and Tailless/Huckebein

    Segmentation Genes

    • Maternal Effect (ME) Genes: Activate zygotic segmentation genes.
    • Gap Genes: Lack large sections of segmented body.
    • Pair-rule Genes: Lack every other segment.
    • Segment Polarity Genes: Defects in, duplications and polarity reversals in every segment.

    Practice Problems

    • Various Drosophila development practice problem questions to identify the roles of genetic mechanisms.

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    Related Documents

    Drosophila Development Lecture Notes PDF

    Description

    Explore the fascinating processes of Drosophila oogenesis and fertilization in this quiz. Uncover the roles of nurse cells, the mechanisms to prevent polyspermy, and the unique features of sperm entry. Perfect for students studying developmental biology.

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