Chick Embryo Development (BIO 133) PDF

Chick Embryo Developmen t BIO 133 Developmental Biology (Animal) Outline 18-hr Chick Embryo 24-hr Chick Embryo 33-hr Chick Embryo Chicken Egg Anatom y A. Upper view of the germinal vesicle B. cross section before gastrulation C. cross section during gastrulation ap = area pellucida ao = area...

Chick Embryo Developmen t BIO 133 Developmental Biology (Animal) Outline 18-hr Chick Embryo 24-hr Chick Embryo 33-hr Chick Embryo Chicken Egg Anatom y A. Upper view of the germinal vesicle B. cross section before gastrulation C. cross section during gastrulation ap = area pellucida ao = area opaca ps = primitive streak 1 = Epiblast (forms the ectoderm) 2 = Blastocoel 3 = Hypoblast (forms the endoderm) 4 = Subgerminal cavity, 5 = Yolk 1. Cleavage in birds is discoidal meroblastic. cleavage occurs in blastodisc. equatorial and vertical cleavage divide the blastoderm into a tissue that is to 5-6 cell layers thick 2. A two-layered blastoderm is formed via ingression and delamination Subgerminal cavity= space between the blastoderm and the yolk Area pellucida= the translucent central area of the blastoderm where embryo develops Area opaca= the peripheral opaque area that surrounds the area pellucida of a vertebrate embryo responsible for the loss of the regulative ability of the primitive-streak-stage embryo 3. The primitive streak defines the axis of the embryo Primitive streak- thickening of the epiblast at the posterior region of the embryo Formed by the ingression of endodermal precursors from the epiblast and migration of cells from the lateral region it elongates towards the future head region thickest at the anterior end, called the Hensen’s node Defines the axis of the embryo  Primitive groove- depression within the streak opening through which migrating cells pass into the blastocoel Analogous to amphibian blastophore Primitive knot-Hensen’s node Thickening at the anterior end functional equivalent of the dorsal lip of the amphibian blastopore (i.e., the organizer) Primitive pit-funnel-shape depression at the center of the node Where cells pass into the blastocoel 4. The primitive streak has a continually changing cell population. Cell migrating thru the Hensen’s node pass down to the blastocoel and migrate anteriorly= foregut, head mesoderm and notochord Cell passing thru the lateral portions of the primitive streak= endodermal and mesodermal tissues Scatter factor- 190kDa protein which enables EMT to happen  5. Migration through the primitive streak: formation of endoderm and mesoderm First cells to migrate thru the Hensen’s node= pharyngeal endoderm of the foregut Germinal crescent-contains precursor of the germ cells Cells that migrated anteriorly and eventually displaced the hypoblast cells to be confined in the anterior portion of the area pellucida Head mesenchyme and prechordal plate mesoderm- enters the blastocoel and do not move ventrally Head process-anterior midline region of the epiblast chordamesoderm-extends upp to the presumptive midbrain; where hindbrain and trunk form Cell migrating inwardly thru the lateral portion of the primitive streak Deep layer=endodermal organs + mostextraembryonic membranes spreads between endoderm and epiblast=- mesodermal portions+ extraembryonic membranes 18-hr Chick Embryo Embryology of chicken 18 hours after fertilization: stained whole mount preparation 1 = Proamnion 2 = Area opaca (dark) 3 = Area pellucida (transparent) 4 = Embryonal region 5 = Neural plate 6 = Chorda 7 = Hensen's node 8 = Primitive streak Embryology of chicken 20 hours after fertilization: stained whole mount preparations 1 = Proamnion 2 = Area opaca (dark) 3 = Area pellucida (transparent) 4 = Embryonal region 5 = Head fold 6 = Neural groove 7 = Neural plate 8 = Chorda 9 = Hensen's node 10 = Primitive streak 1. An area of the blastoderm at the cephalic end of a vertebrate embryo, in which there is no mesoderm separating the ectoderm and endoderm. 24-hr Chick Embryo 24-hr Chick Embryo 1. 4 pairs of somites 2. At this stage the dark peripheral area opaca and central translucent and colourless area pellucida are distinctly visible. 3. In the anterior part is present the proamnion, which is a small and comparatively more translucent region of area pellucida and is characterised by the absence of mesoderm. 4. In the middle of area pellucida, in its posterior half runs a primitive streak with a primitive groove in its centre. The primitive groove is bound by primitive folds. 5. In the anterior half of area pellucida, in the middle, runs the neural groove bound by neural folds. 6. The primitive streak and neural groove are separated by Hensen’s node having a small depression in the centre-the Hensen’s pit.  24-hr Chick Embryo 7. Immediately below the primitive groove the primitive streak gives rise to a small out- growth, the notochord and on either side to mesoderm. 8. In the area pellucida embryonic and extra embryonic regions also become distinguished. 9. In the anterior- most part the ectoderm has given rise to head fold, which is a pocket-like extension of neural folds. The underlying endoderm is also transformed into a pocket-like foregut. The proamnion is greatly reduced. 10. In front of Hensen’s node the mesoderm of embryonic area differentiated into 3-4 pairs of mesodermal somites. 11. The neural canal, in the region of head fold, gives rise to forebrain. 12. The foregut extends on either side into an amino-cardiac vesicle. 3 – neural folds (neurectoderm) 8 – cranial neuroporus 4 - (epidermal) ectoderm 9 – foregut 6 – endoderm 10 – subcephalic cavity (amnion region) 7 – neural groove 11 – subgerminal cavity 2 – (ch) chordamesoderm 3 – (nt) neural tube 4 – (ec) ectoderm 5 – head mesoderm 6 – (en) endoderm 2 – chordamesoderm 3 – neural folds 1 - primitive groove 33-hr Chick Embryo Whole mount Whole mount Whole mount FATES 1. Prosencephalon Gives rise to: A. TELENCEPHALON - this gives rise to -> Cerebral hemispheres, Basal ganglia, Olfactory bulbs, Lateral ventricles B. DIENCEPHALON- Thalamus, Hypothalamus, Epithalamus (pineal gland), subthalamus C. OPTIC CUP Formation of optic cup i. Optic Vesicle development - The optic vesicles emerge as lateral outgrowths from the diencephalon (forebrain). - These vesicles grow outward toward the surface ectoderm. ii. Lens placode induction - The extreme lateral portion of the optic vesicle comes into contact with the overlying ectoderm.This interaction induces the thickening of the ectoderm to form the lens placode. iii. Invagination of the Optic vesicle - The optic vesicle begins to invaginate, forming a cup-like structure called the optic cup. - The invagination also occurs in the lens placode, which later separates to become the lens vesicle. NOTE: Infundibulum: funnel-shaped structure that connects the developing hypothalamus to the developing pituitary gland (hypophysis) during early embryonic development. Give rise to pituitary gland and infundibular stalk 2. Mesencephalon Gives rise to: A. TECTUM - integrates sensory information and reflexes related to vision and hearing. B. CEREBRAL AQUEDUCT - Connects 3rd to 4th ventricle C. TEGMENTUM - involved in motor coordination; important for reward, addiction, and movement regulation; transmit motor information from the cortex to the spinal cord. 3. Rhombencephalon Gives rise to: A. METENCEPHALON - Cerebellum - responsible for motor coordination, balance, and fine motor control Pons - Serves as a relay station for signals between the forebrain and the cerebellum Cerebral aqueduct - plays a role in circulating cerebrospinal fluid (CSF) B. MYELENCEPHALON- Medulla oblangata - Responsible for vital autonomic functions like heart rate, breathing, and blood pressure regulation; Houses the centers for reflexes such as swallowing, vomiting, and coughing; It contains ascending and descending tracts that carry sensory and motor information between the brain and spinal cord. 4th ventricle - located between the cerebellum and the pons and becomes part of the central canal of the spinal cord. NOTE: AT the 33-hour stage of embryonic development in many vertebrates (e.g., chick embryos), the rhombencephalon (hindbrain) is divided into seven neuromeres, called rhombomeres. These rhombomeres are transient, segmental structures that play a critical role in organizing the development of the cranial nerves and brainstem. FATE OF THE ECTODERM 1. Neuroectoderm (Nervous System) Fate: The neuroectoderm gives rise to the central nervous system (CNS) and peripheral nervous system (PNS). A. Brain and spinal cord: The neural tube forms from the neuroectoderm and eventually develops into the brain and spinal cord. The process of neural tube formation is called neurulation. B. Peripheral nervous system: The neural crest cells (which arise from the neuroectoderm) give rise to a variety of structures, including sensory ganglia (e.g., dorsal root ganglia) Autonomic ganglia Schwann cells (which myelinate peripheral nerves) Chromaffin cells of the adrenal medulla Facial cartilage and bone FATE OF THE ECTODERM 2. Surface Ectoderm (Epidermis and Appendages) Fate: The surface ectoderm forms the epidermis (outer layer of the skin) and its appendages, as well as other sensory organs A. Epidermis: Forms the outermost layer of the skin, providing a protective barrier. B. Hair, nails, and glands: The surface ectoderm gives rise to structures such as hair follicles, sebaceous glands, sweat glands, and nails. C. Mucous membranes: It forms the lining of the oral cavity, nasal cavity, and the anus. D. Sensory organs: The surface ectoderm also contributes to the formation of the lens of the eye and epithelial lining of the ear (e.g., tympanic membrane). FATE OF THE ECTODERM 3. Placodes (Specialized ectodermal structures) Fate: Some regions of ectoderm thicken to form placodes, which are specialized areas that give rise to sensory organs and components of the nervous system. A. Olfactory placodes - Give rise to the olfactory epithelium (responsible for the sense of smell). B. Lens placode: Forms the lens of the eye. C. Auditory placodes: Give rise to the structures of the inner ear, including the cochlea and vestibular system, which are involved in hearing and balance. 4. Other contributions of ectoderm A. Teeth: The ectoderm contributes to the formation of the enamel of teeth. B. Pituitary gland: The anterior part of the pituitary gland (also known as the adenohypophysis) is derived from ectodermal tissue. C. Cornea: The epithelial layer of the cornea is formed by the surface ectoderm. FATE OF THE OTIC PLACODE The otic pit becomes increasingly pronounced as the surrounding ectoderm continues to grow, and the inner cells proliferate. By the end of 33 hours, the pit is well-formed, and the invagination is almost complete. 1. Induction and Ectodermal Thickening (24-28 hours) - The otic placode forms as a localized area of thickened ectoderm, located on either side of the hindbrain, in the region that corresponds to the rhombomeres of the developing brainstem (specifically, around rhombomeres 5 and 6). - The placode begins to flatten and differentiates from the surrounding ectoderm. FORMATION OF THE OTIC PLACODE 2. Invagination and Formation of the Otic Pit (28-30 hours) - Around 28-30 hours, the otic placode undergoes invagination. - This process involves the ectodermal cells of the otic placode folding inward to form a cup-like structure known as the otic pit. - The formation of the otic pit is a significant step that marks the transition from a flat placode to a more three-dimensional structure. - The surrounding ectoderm continues to stay attached, but the center of the placode deepens as the cells change shape. FORMATION OF THE OTIC PLACODE 3. Growth and Deepening of the Otic Pit (30-33 hours): - Between 30-33 hours, the otic pit continues to deepen, and its lateral edges converge toward each other. - The otic pit becomes increasingly pronounced as the surrounding ectoderm continues to grow, and the inner cells proliferate, pushing the edges closer together. - By the end of 33 hours, the pit is well-formed, and the invagination is almost complete. FATE OF THE MESODERM 1. Paraxial Mesoderm (Somitomeres and Somites): Fate: Forms structures associated with the axial skeleton and musculature. Somites: These segmented blocks of paraxial mesoderm give rise to:Sclerotome: Forms the vertebrae and rib cartilage. Myotome: Forms the skeletal muscles of the body (e.g., muscles of the back and limbs). Dermatome: Forms the dermis of the skin. FATE OF THE MESODERM 2. Intermediate Mesoderm Fate: Forms structures related to the urinary system and reproductive system. Kidneys: Forms the kidneys and ureters. Gonads: Gives rise to the testes (in males) and ovaries (in females), as well as the genital ducts. Part of the adrenal glands and mesonephros (temporary kidney in early development). FATE OF THE MESODERM 3. Lateral Plate Mesoderm The lateral plate mesoderm is divided into two layers: the somatic (parietal) layer and the splanchnic (visceral) layer. A. Somatic (Parietal) Layer: Fate: Forms the body wall, including the limbs and skin. It contributes to the formation of: Skeletal muscles of the body and limbs, Dermis of the skin, Bones of the limbs and body wall, Lining of the body cavities (peritoneum, pleura, and pericardium). B. Splanchnic (Visceral) Layer: Fate: Forms the visceral organs and the vascular system. It contributes to the formation of: Heart and blood vessels, Smooth muscles of internal organs (e.g., gastrointestinal tract, respiratory system, and blood vessels), Mesenteries (membranes that support the organs within the body cavity) FATE OF THE MESODERM 4. Notochord Fate: The notochord itself is a transient structure, but it plays a crucial role in signaling and patterning the surrounding tissues during development. It will eventually degenerate in most species but contributes to the formation of the nucleus pulposus of the intervertebral discs in adults. FATE OF THE HEART At around 20 hours in the chick embryo, the pre-cardiac mesoderm starts to fold and merge to form a simple, linear heart tube. The heart tube consists of an inner layer of endocardium (the endothelial lining) and an outer layer of myocardium (muscle tissue). As the heart tube forms, it undergoes convergent extension, a process that lengthens and narrows the tube. This movement helps bring the two parts of the heart field together, forming the heart tube. At about 24-30 hours in the chick embryo, the linear heart tube begins to undergo looping, a crucial step in heart development. FATE OF THE HEART This process is essential for shaping the heart and establishing its functional chambers. Rightward looping: The heart tube bends and loops to the right, creating distinct bulges that correspond to the future chambers. The looping helps position the different segments of the heart The sinus venosus (future atria) atria ventricles outflow tract (which will eventually form the aorta and pulmonary artery. FATE OF THE ENDODERM 1. Formation of the Gut Tube The endoderm begins to fold and form the primitive gut tube, which will give rise to the entire digestive tract. At this point, the gut tube is in its early form, and it will eventually differentiate into the: Foregut: This section will give rise to the pharynx, esophagus, and part of the stomach. Midgut: This will eventually develop into most of the small intestine and the cecum. Hindgut: The hindgut will differentiate into the large intestine, the rectum, and eventually the anus. 2. Lung Bud Development The endodermal cells in the region of the foregut begin to form the lung buds, marking the early stages of the development of the respiratory system. These lung buds will eventually give rise to the bronchi and lungs. FATE OF THE ENDODERM 3. Formation of the Liver and Pancreas At this stage, the liver and pancreas are beginning to develop from the endoderm of the foregut: - The liver arises from a small liver bud in the ventral wall of the foregut. - The pancreas starts to develop as an outgrowth from the dorsal part of the foregut. It will later split into the exocrine and endocrine components. 4. Formation of the Thyroid Gland The endoderm is also contributing to the formation of the thyroid gland. The thyroid rudiment forms in the region of the pharynx from the endodermal tissue at this stage. FATE OF THE ENDODERM 5. Formation of the Parathyroid Glands The parathyroid glands begin to differentiate from the endodermal tissue in the region of the pharyngeal pouches. 6. Development of the Urogenital System In the early stages, the endoderm contributes to the epithelial lining of the urogenital system, including the bladder and parts of the urethra. VIEL GLÜCK! BIO 133 Developmental Biology (Animal)