Chapter 13.1. Chick Development
Page 1: Introduction to Chicken Development
Vertebrate Development: Focus on the development of chickens, specifically the species Gallus gallus.
Page 2: Amniotes
Amniotes: Group of vertebrates that includes reptiles, birds, and mammals.
Characteristics: Have an amniote egg that allows for terrestrial reproduction.
Types of Amniotes:
Reptiles: An example is the chicken.
Birds: Characterized by feathers and flight.
Monotremes: Egg-laying mammals (like platypus and echidna) that possess mammary glands.
Placental mammals: Examples include Mus musculus (house mouse).
Page 3: Extraembryonic Membranes
Amniote Egg Development: Membranes form during the development of reptiles, birds, and mammals.
Types of Extraembryonic Membranes:
Yolk Sac: Provides nutrients.
Chorion: Contains blood vessels, functions in respiration, contributes to placenta in placental mammals.
Allantois: Waste storage.
Amnion: Encloses the embryo in a protective fluid.
Shell and Amniotic Cavity: Protects and contains the embryo.
Page 4: Amnion and Yolk Sac
Amnion: A membrane surrounding the chick embryo, providing a fluid cushion and preventing desiccation.
Yolk Sac: In chickens, encases the yolk and features blood vessels for nutrient absorption.
Page 5: Allantois and Chorion Functions
Allantois: Functions mainly to store waste produced by the embryo.
Chorion: Contains blood vessels that facilitate gas exchange, absorbing oxygen and releasing carbon dioxide; forms part of the placenta in placental mammals.
Page 6: Structure of the Chick Egg
Blastodisc: A small disc of cytoplasm on the surface of the yolk that undergoes division.
Components:
Chalaza: Helps stabilize the yolk.
Albumin: Egg white that provides additional nutrients.
Vitelline Membrane: Surrounds the yolk.
Shell Membranes & Air Space: Protect the contents.
Page 7: Early Cell Division
Cell Division: Early stages show a 1-cell thick layer except at the edges.
Areas of the Blastodisc:
Area pellucida: Clear central zone.
Area opaca: Peripheral zone.
Marginal zone: Outer edge of the disk.
Page 8: Cell Layer Formation
Cell Layers: Early cell divisions lead to a fluid-containing blastocoel below the single-layered upper epiblast.
Page 9: Developmental Similarities
Pre-gastrulation and Gastrulation: Similarities between chicken and mammalian development, particularly in extraembryonic membranes and cell movements during gastrulation.
Page 10: Formation of the Hypoblast
Hypoblast Formation: Some cells migrate to the subgerminal cavity to contribute to the hypoblast as the egg is laid.
Page 11: Layers and Structures
Blastoceal: Space found between the upper epiblast and lower hypoblast.
Only Epiblast: Responsible for forming the embryo.
Page 12: Hypoblast Development Stages
Development Stages: Hypoblast islands begin to form; sequential stages classify the variety of layers.
Page 13: Primitive Streak Initiation
Primitive Streak and Groove: Important process in birds and mammals, where cells migrate to the disk's center, producing the thickening known as the primitive streak and groove.
Page 14: Cell Migration to Blastocoel
Cell Movement: Involves individual migration through the primitive groove, transitioning from an epithelial to a mesenchymal state, with changes in cadherin expression.
Page 15: Stages of Formation
Stages: Various stages of development showing the formation of the primitive streak and relationships among epiblast, hypoblast, and other structures.
Page 16: Early Stages of Cell Movement
Cell Movements: Formation of the primitive streak is associated with the migration of cells from the marginal zone towards the center of the blastoderm.
Page 17: Endodermal and Mesodermal Cells Migration
Cell Distribution: Endodermal and mesodermal cells migrate through the primitive streak, with some integrating into the hypoblast and others forming a loose layer in the blastocoel.
Page 18: Future Endoderm Formation
Endoderm Formation: Some migrating cells displace existing hypoblast cells to form the future endoderm.
Page 19: Role of Hensen’s Node
Hensen's Node: Anterior segment of the primitive streak serves a role similar to the dorsal blastopore lip in frogs, demonstrating early embryonic development processes.
Page 20: Fate Mapping
Fate Map: Cell movements during the primitive streak can be mapped, showing differentiation into various structures including notochord and mesoderm layers.
Page 21: Developmental Progression
Anatomical Structures: Illustrates how anterior and posterior embryonic structures form at different development stages.
Page 22: Asymmetry in Development
Embryonic Axis and Timing: Anterior regions develop earlier than posterior regions based on the timing of cell migration through the primitive streak during gastrulation.
Page 23: Layers of the Developing Embryo
Gastrulation Phase: Formation of three definitive layers: ectoderm, mesoderm, and endoderm, with migration dynamics affecting overall morphology.
Page 24: Embryonic Structures
Embryonic Anatomy: Overview of key structures such as the heart and amniotic cavity, vital for development.
Page 25: Hensen's Node Functionality
Cell Signaling and Organizers: Hensen’s node can induce axial development when transplanted, similar to the organizer function in frogs.
Page 26: Organizer Signaling Molecules
Molecular Functions: Chordin and Noggin from Hensen's node inhibit BMP signaling, enhancing dorsal tissue formation, yet requiring FGF for neural specification.
Page 27: Role of Noggin
Signaling Pathways: Interactions of Noggin with BMP signaling crucial for neural induction processes in chicks.
Page 28: FGF Signaling
Fibroblast Growth Factors (FGF): Produced in early embryonic stages; they are essential for neuronal gene expression in targeted areas of the embryo.
Page 29: Retinoic Acid Dynamics
Retinoic Acid: A hydrophobic signaling molecule derived from vitamin A, serves as a morphogen affecting gene expression gradients along the anterior-posterior axis.
Page 30: Gradients and Morphogenic Effects
Morphogen Gradient: Only low concentrations enhance anterior development, while high levels promote posterior specifications.
Page 31: Hox Gene Expression
Hox Genes: Critical for determining body plan in vertebrates; retinoic acid influences expression patterns of these genes during development.
Page 32: Homology Across Species
Homologous Genes: Comparison of vertebrate Hox genes to Drosophila homeotic genes highlights evolutionary conservation and functional roles in development.
Page 33: Regional Hox Expression
Differential Hox Expression: Specific Hox genes such as Hoxb4 and Hoxb9 are expressed at defined embryonic stages, reflecting varying developmental roles in the anterior-posterior axis.