Chapter 9. Drosophila Flash Cards

Page 1

Drosophila Development Overview

• Focus on genetics in Drosophila development.

• Reading: Chapter 9, pages 273-290, 295-296.

Page 2

Importance of Drosophila in Development Studies

• Drosophila provides unique insights into developmental genetics compared to other organisms like sea urchins.

• While manipulating cells is challenging, genetic studies are straightforward.

• Mutations serve as tools to understand affected genes' roles in development.

• Many critical development-regulating genes in humans were first identified in Drosophila.

Page 3

Drosophila Life Cycle

• Stages: embryo → larva → adult.

• Body Structure:

  • Head

  • Thorax:

    • Prothorax (T1)

    • Mesothorax (T2)

    • Metathorax (T3)

  • Abdomen (A1-A8)

Page 4

Drosophila Anatomy

• Adult consists of:

  • 3 body regions:

    • Head (red)

    • Thorax (green)

    • Abdomen (orange)

  • Each region comprises structurally distinct segments.

Page 5

Head and Thorax Structure

• Head:

  • 3 segments (less visible)

  • Contains eyes, antennae, proboscis.

• Thorax:

  • 3 segments, each having a pair of legs (total 6).

  • 2nd thorax segment has wings.

  • 3rd thorax segment has halteres for balance.

• Abdomen:

  • Composed of 9 segments (A1 to A9).

Page 6

Nuclear Organization in Early Embryos

• Nuclei are arranged in early fly embryos (cell cycle numbers refer to divisions).

• Syncytial embryos until nuclear division 13.

Page 7

Early Cell Division in Embryos

• Development from fertilized egg to larva occurs within 24 hours.

• Yolk is centered in the egg; cleavage is unusual—nuclei divide multiple times without membrane formation.

• Syncytial stage: many nuclei without cell membranes.

• 256 nuclei result from 8 divisions, each taking about 8 minutes.

Page 8

Nuclear Migration and Membrane Formation

• Nuclei migrate beneath the outer membrane by division 10, forming a syncytial blastoderm.

• Midblastula transition occurs after the 10th division, leading to increased transcription of mRNA.

• After division 13, membranes encase nuclei, forming a yolk core surrounded by a single cell layer.

Page 9

Nuclear Division in Fly Embryos

• Diagrammatic representations (A, B, C, D) illustrate nuclear division processes in syncytial development.

Page 10

Fly Gastrulation: Initial Stages

• Diagram illustrates internal ectoderm, amnioserosal covering, and pole cells.

• Development of ventral furrow initiates gastrulation process.

Page 11

Gastrulation Process

• Begins post-midblastula transition.

• Ventral midline folds inward, shaping future endoderm and mesoderm.

• Contrasts with processes in sea urchins; blastopore appears stretched along the embryo.

Page 12

Continued Gastrulation

• Body segments arise during gastrulation.

• Nervous system originates from the ventral ectoderm, positioned ventrally as opposed to dorsally in vertebrates.

Page 13

Nervous System Development

• Body segmentation occurs; the nervous system forms from parts of the ventral ectoderm.

Page 14

Segment Formation and Gastrulation

• Formation of various embryonic structures, highlighting anterior midgut invagination and cephalic and ventral furrows.

Page 15

Segment Identification in Classical Studies

• Detailed diagrams showing segmentation and body structure (A8, T1, T2, T3).

• Identification of medial and lateral segments of Drosophila.

Page 16

Key Genetic Materials in Development

• Roles of maternal effect genes, gap genes, pair-rule genes, segment polarity genes, and homeotic genes in anterior-posterior axis development.

Page 17

Developmental Organization

• Key tasks for establishing the anterior-posterior axis:

  • Specification of body ends.

  • Dividing segments appropriately.

  • Differentiating segments along the body.

Page 18

Anterior-Posterior Axis Specification

• Stepwise formation of spatial organization with:

  • Maternal effect genes establishing the axis.

  • Gap genes dividing areas into broad segments (mutations cause gaps).

  • Differentiation through homeotic genes.

Page 19

Key Genes in Development

• Discussion of maternal effect gene proteins, gap gene proteins, and pair-rule proteins' roles in segmentation processes.

Page 20

Maternal Effect Genes

• Maternal effect genes are crucial for setting the anterior-posterior axis, with impacts observable on embryos based on maternal mRNA/proteins deposited.

Page 21

Protein Gradients and Axis Formation

• The anterior-posterior axis is developed via gradients created by bicoid and nanos proteins.

Page 22

Bicoid Protein Characteristics

• Description of bicoid as a homeodomain protein and its function in establishing body polarity via transcription factors within a 60 amino acid homeodomain.

Page 23

Experimental Validation of Bicoid's Role

• Experimental results showing head development dependency on bicoid gene, including comparisons between normal and mutant phenotypes.

Page 24

Bicoid mRNA Manipulation in Experiments

• Results of adding bicoid mRNA at varying embryo locations, illustrating altered head and tail development in mutants.

Page 25

Bicoid Protein Gradients

• Concentration and spatial distribution of bicoid mRNA and its direct relationship with the anterior-posterior setup.

Page 26

Analysis of Bicoid Concentration

• Graphical insights into bicoid concentrations and their influence across wild-type and mutant embryos.

Page 27

Mechanism of Bicoid Action

• How bicoid inhibits the translation of posterior structures (caudal) and its implications for anterior-posterior development.

Page 28

Bicoid's Multifaceted Role

• Explanation of bicoid's interactions with caudal mRNA for translation inhibition and transcription activation of hunchback.

Page 29

Distribution of Caudal Protein

• Visual representation of caudal protein distribution in response to bicoid actions.

Page 30

Hunchback Transcription Activation

• Role of bicoid in triggering hunchback transcription, crucial for thorax and head regions development.

Page 31

Concentration Variances Across Embryos

• Comparison of oocyte mRNAs and embryo protein concentrations of significant developmental markers.

Page 32

Nanos Protein in Axis Formation

• The significance of nanos in establishing the posterior axis via mRNA localization and translating inhibition of hunchback.

Page 33

Identification of Segments

• Research insights on how specific segments in fly larvae are distinguishable in mutant analyses.

Page 34

Gap Genes in Segment Development

• Gap gene Krüppel example illustrating mutations leading to segmentation pattern gaps.

Page 35

Function of Gap Genes

• Morphological segmentation via gap genes characterized by how their mutations lead to segment absence.

Page 36

Regulatory Interactions Among Gap Genes

• Explanation of gap genes' initial transcription being controlled by maternal effect genes and their mutual regulation.

Page 37

Interaction of Gap Gene Products

• Visual representation of how gap gene products interact during segment development.

Page 38

Interactions of Gap Gene Products Continued

• Detailed assessment of gap gene concentration variations along the embryo.

Page 39

Regulating Development with Gap Genes

• Focusing on the distribution of gap gene products and their historical significance in Drosophila development.

Page 40

Overview of Genetic Regulation

• Summary of how maternal effect, gap, pair-rule, segment polarity, and homeotic genes work in anterior-posterior organization.

Page 41

Homeotic Genes and Segment Identity

• Examination of homeobox genes' effects on segment differentiation alongside mention of specific mutations.

Page 42

Homeotic Genes Example

• Comparative images showing wild-type and altered head structures from the Antennapedia mutation.

Page 43

Homeotic Genes Localization

• Identification of homeotic gene clusters along Drosophila chromosome 3 influencing segment types along the body axis.

Page 44

Regulation of Homeotic Gene Expression

• Discussion on regulatory sequences affecting the expression of homeotic genes by gap genes at anterior/personal body regions.

Page 45

Interactions Among Homeotic Genes

• Insight into how homeotic genes influence each other's expressions in different segments.

Page 46

Case Study: Ultrabithorax and Antennapedia

• Effects of Ultrabithorax on Antennapedia expression revealing broader developmental implications when absent.

Page 47

Mutant Analysis

• Example of a fly lacking expression of the ultrabithorax homeobox gene and its overall developmental impact.

Page 48

Role of Homeotic Genes in Development

• Explanation of how homeotic genes govern the expression of specific developmental genes associated with structures or tissues, using antennapedia and eyeless as examples.

Page 49

Development of Wing Structures

• Impact of homeotic gene ultrabithorax on segment development that normally leads to the formation of small balance structures called halteres.

Page 50

Key Developmental Regulatory Genes

• Insight into gene classifications including selector, regulator, and realizator, alongside associated processes related to cell polarity and adhesion.