Chapter 32. Embryology
Recommended Article : 【Biology】 Table of Contents for Biology
1. Overview
h. Hydra Regeneration and Transplantation
1. Overview
⑴ Model Organisms for Developmental Research
① Fruit Fly (Drosophila melanogaster) : Embryo develops outside the mother
② C. elegans
③ Xenopus laevis
④ Chick : Surgical removal possible during embryo development
⑤ Mus musculus
⑥ Danio rerio : Transparent interior
⑦ Arabidopsis thaliana
⑵ Key Proteins
① Fibronectin
○ Located in the extracellular matrix
○ Stretches when the organ grows in length
○ Binds with the integral protein integrin
② Cadherin
○ Attaches cells to form tissues and organs
○ Involved in neural tube separation
③ Morphogen Proteins (BMP Antagonists)
○ noggin, chordin, xnr3
④ Morphogen Proteins (Wnt Antagonists)
○ cerberus, Fribee, dickkopf, Frzb
○ Note: Wnt is related to deep brain structures
2. Genetic Identity
⑴ Basis of Genetic Identity
① Totipotency in plants
② Nuclear transfer in animals
○ Briggs & King’s experiment: Concluded changes in nuclear activity occur after significant development
○ Gurdon’s experiment: Induced development even with differentiated cell nuclei
③ Reproductive cloning in mammals
④ Differentiation potential of stem cells
○ Stem cell: Ability to differentiate into specific cell types
○ Unipotency: Ability to differentiate into only one type of cell
○ Multipotency: Ability to differentiate into several types of cells
○ Pluripotency: Ability to differentiate into all cell types
○ Totipotency: Ability to develop into a complete organism, including extraembryonic structures
⑵ Types of Stem Cells
① Type 1: Embryonic Cells
○ Definition: Blastomeres themselves
○ Trophoblast cells + Inner cell mass. Totipotency
② Type 2: Embryonic Stem Cells (ESC)
○ Definition: Cells obtained during embryo differentiation
○ Advantages: Pluripotency
○ Disadvantages: Ethical issues (considered up to blastocyst stage, but still ethical concerns)
○ Types: Oocyte-derived ESC, Parthenogenetic ESC, Virgin-born ESC, Somatic cell nuclear transfer ESC
○ Oocyte-derived ESC: Inner cell mass taken from the blastocyst
○ Virgin-born ESC: Eggs develop without sperm. Dr. Hwang Woo-suk’s research
○ History
○ Established in 1981 from mouse blastocysts
○ In 1998, Thomson et al. established human embryonic stem cells (hESC) for the first time
③ Type 3: Adult Stem Cells (ASC)
○ Definition: Stem cells found in adults
○ Note: The environment around adult stem cells is referred to as the niche
○ Advantages: No ethical concerns
○ Disadvantages: Multipotency, Unipotency
○ Hematopoietic Stem Cells (HSC)
○ Differentiates into white blood cells, red blood cells, platelets, etc.
○ Associated with malignant blood disorders, severe aplastic anemia, etc.
○ CD34+
○ Mesenchymal Stem Cells (MSC)
○ Derived from mesoderm, forms bone, cartilage, muscle, blood vessels, fat, etc.
○ Differentiates into skin, muscle tissue, and even nerve tissue
○ Related to joint cartilage damage, bio-material production, and nervous system disorders
○ CD73+, CD90+, CD105+
○ Bone Marrow Stem Cells
○ Composed of hematopoietic stem cells: Differentiates into white blood cells, red blood cells, macrophages
○ Procedure takes 30 minutes
○ Normal daily activities possible immediately after the procedure
○ Neural Stem Cells
○ Also present in the adult nervous system
○ Skin Stem Cells
○ Cord Blood Stem Cells (CBC)
○ Derived from fetuses with undeveloped immune systems. Extracted from placenta and umbilical cord blood
○ No immune rejection
○ Active
○ Assists in regenerating damaged cartilage tissue
○ Type 1: Hematopoietic Stem Cells
○ Type 2: Mesenchymal Stem Cells
○ Low-grade GVHD
○ Umbilical Cord Stem Cells
○ No immune rejection
○ Type 4: Induced Pluripotent Stem Cells (iPSC)
⑤ Type 5: Terminally Differentiated Cells
⑶ Determination: Point of Cellular Differentiation Through Gene Expression (e.g., MyoD1 Expression)
① Autonomous Determination: Determination from the beginning (e.g., protostomes, deuterostomes)
○ Example: Concentration distribution of cytoplasmic determinants in the egg becomes uneven after fertilization
② Conditional Determination: Determination influenced by surrounding cytoplasmic factors during development
○ Cell differentiation can be induced by signaling molecules from neighboring cells
3. Developmental Process
⑴ Overview
① Step 1: Cell Division
② Step 2: Cell Differentiation
③ Step 3: Morphogenesis
④ Step 4: Pattern Formation
⑵ Activation of Ovum
① Early Ovum Activation: Before fertilization
○ Uses NADPH to form the vitelline membrane, activating NAD+
○ Inactivates MAPK → Pauses cell division → Prepares for proper fertilization, initiates DNA replication
② Late Ovum Activation: After fertilization
○ Insufficient time for direct transcription → Transfers mRNA to the cytoplasm → Produces proteins required for fertilization → Immediate transcriptional inhibition effect is absent
○ Transcription occurs after the blastula stage, so transcriptional inhibitors take effect at this stage
○ Protein production occurs at higher pH levels, so Na+/H+ exchange pump → pH increase
⑶ Blastula
① Blastula has a blastocoel
② Blastocoel degenerates and disappears soon after
⑸ Gastrulation: Formation of the Embryonic Germ Layers
① Gastrulation: Ingression
○ Morphogen: A substance that, as it diffuses, creates concentration gradients, determining cell fate based on exposure level to the gradient
② Germ Layers
○ Neural tube induction
○ Surface ectodermal cells: Ectoderm
○ Archenteron dorsal lip (dorsal lip of the blastopore): Mesoderm, endoderm
○ (Note) Neural crest: Ectoderm
○ (Note) Neural crest: Mesoderm
○ (Note) Neural crest: Ectoderm
○ Endodermal cells: Endoderm
③ Formation of the Germ Layers Mechanism
○ Extensive cell movement
○ Archenteron: Degenerates and disappears. Replaced by the endoderm
○ Formation of embryonic layers
⑹ Germ Layer Theory
Figure. 1. Formation of the Germ Layers
① Ectoderm : Epidermis, nervous system, brain, pigment cells, lens of the eye, adrenal medulla
② Mesoderm : Muscles, nephric duct, somite, heart, connective tissue, kidney (metanephros), circulatory system, bones and skeletal muscles, adrenal cortex, dermis
③ Endoderm : Respiratory system, digestive system, endocrine glands, bladder
○ Note: The liver, lungs, intestines, etc., are all endodermal, but only the kidney is mesodermal
④ Germ cells: Sperm and egg cells. Not part of the germ layers
Input: 2015.07.15 08:11