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Developmental Zoology (ZOO 228.1.0) Dr. Dinithi Peiris Dept. of Zoology University of SJP 1 Developmental Zoology Unit Type No: of Lecture Hours Instructor Attendance 2 Course Description How does a complex, multicellular organism arise from a single cell? What is known about the mechanisms that accomplish this feat? : Compulsory Course : 15 hrs : Dr Dinithi Peiris : 80% attendance This course aims to provide a broad look at development integrating. We will explore the basic body plan of the embryo and how organs are formed, with special emphasis on vertebrate models. Embryonic and Adult Stem Cells will also be covered Prerequisite- Zoo 123.1.0 - Cytology 3 4 1 Intended Learning Outcomes Intended Learning Outcomes Upon successful completion of this course students should be able to Describe process of gametogenesis, fertilization, implantation Upon successful completion of this course students should be able to Describe the regulatory mechanisms of morphogenesis in early animal embryos. Understand the basis of development of animal body, and molecular mechanisms regulating developmental processes. phenomena relating animal development including axis formation, cell differentiation, and morphogenesis. Understand various aspects of tissue interactions observed in organs in later stages of embryonic development Describe 5 6 Assessment References Assignment 1: Tutorial (10%) Must complete the assignment 1 to sit for the final theory exam. • • Methods of Assessment: 1. Mid term exam 2. Tutorial 3. One hour final exam Slack J. (2001) – Essential developmental biology. Blackwell publications. USA. (20%) (10%) (70%) • Gilbert S. (2002) biology, 9th Edition. Online – Developmental resources -http:// www.nature.com/milestones/development/ milestones/index.html 7 8 2 What is Animal Development What is Animal Development Developmental Biology is the study of a PROCESS whereby a single cell divides and selectively activates expression of genes to produce a complex organism composed of many cell types. The process by which a fertilized egg transforms itself into a complex organism is one of the most exciting and complex mysteries in the field of biology! How does it happen?? Each of us sitting in this room developed from a single egg! Ex ovo omnia = all from the egg. 1651 William Harvey proposed that all animals originate from eggs• What are the types of PROCESSES required? 9 10 What is Animal Development What is Animal Development • During development single cell zygote give rise to different cells with different function. • Cells of similar types organized into tissues, tissues into organs, organs into organ systems, & organ systems into whole organism. • Hence, embryonic development must give rise, higher-level structures arranged in a particular way in three dimensions 11 • There is clearly something very special about a fertilized egg cell. • The genes in the genome are the driving force behind development and they are also the basis of the differences between organisms. 12 3 What is Animal Development • Question? • How a single cell and end up with a complex multicellular organism, with hundreds of different cell types, all formed at the correct time and in the correct place to build a functioning body and perform all the individual functions of life. What is Animal Development A central idea of development that we will talk about many times the rest of the semester is DIFFERENTIATION: All cells have the same DNA, but different cells express different genes. This is called DIFFERENTIATION. 13 What is Animal Development 14 Animal Development This PROCESS is studied using TOOLS, many of which you have already heard about: – a) Cell Biology – b) Genetics – c) Molecular Biology - 15 1. The body is made of millions to billions of cells. d) Each cell has a specialized task, e.g. muscle cell, nerve cell, etc. e) To carry out these specialized tasks, each cell has special machinery i. Nerve cell has machinery for transmitting electrical and chemical signals ii. blood cell has machinery to transport oxygen 16 4 Basics? Basics? 2. Cellular machinery is largely made up of proteins Proteins are long chains of amino acids. Each protein molecule has evolved to carry out a particular task. E.g: i. Hemoglobin in the blood binds to & carries oxygen ii Actin forms filaments that make up the cytoskeleton iii Ribosomal proteins help make up the ribosome, the cell's protein factory iv. Insulin is secreted by cells of the pancreas & serves as a signal to other cells. 17 3. Because of their different tasks, different cells contain different proteins: While some proteins are found in all cells (actin), others are made only in specialized cells 18 Basics? Developmental Mechanisms Differentiation mechanism: 4. Proteins are made up of chains or sequences of amino acids, and these amino acids are "encoded" in the cell's DNA a. b. Mosaic Development DNA is organized in large segments known as chromosomes 1 gene encodes = 1protein c. Thus there is a myoglobin gene, an actin gene, an insulin gene etc.. d. Mutations in single genes result in ? 19 Cells acquire fixed identity No influence from neighboring cells Isolated cells develop in to particular part of the body Autonomous Specification 20 5 Developmental Mechanisms Developmental Mechanisms Wilhelm Roux's experiment in 1888 Hans Driesch's experiment in 1892 Regulative Development Sea urchin cells developed in to separate parts. Most organisms combine information & develop as a combination of Mosaic & Regulative process. Cells are flexible Adjust according to neighboring cells & envt. When isolated, each cell can develop in to an entire organism. Conditional Specification 21 22 Developmental Mechanisms Developmental Mechanisms Another way to state the basic question is of Development is: How do cells know which genes to activate as they go through development? What are the two sources of information cells? Different Two cells activate different genes sources of information cells 23 1. Information from your mother 2. Information from your neighbors or environment. 24 6 Developmental Mechanisms Developmental Mechanisms Information from your mother Information from your neighbors or environment. E.g .Gene expression patterns, or Segregation of "determinants • I. Informational molecules (e.g. protein or mRNA). E.g. Cell-cell interactions. Communication can be local, via direct cell-cell contacts, or global, via diffusible molecules . I. Maintain neighbors in quo. II. incite neighbors to novel behaviors ii. Inherited patterns of gene expression. Iii. Information can be passed on uniformly, or can be segregated to one of the progeny cells. III. The differences can then be transmitted to cellular offspring IV. Even unicellular organisms communicate! 25 26 Developmental Mechanisms Signaling Systems E.g. of simple cell-cell communication • Development depend on effects of one group of cells on another. This is exerted by embryonic induction – secrete inducing factors 7 molecular families of inducing factors – growth factors, cytokines or hormones Binding results in induction of signal transduction pathway Leads to activation or suppression of certain genes 28 Yeast sex: Haploid cells have 2 mating types; “a” or “alpha” • Single-celled slime mold Amoeboid type cells living on forest floor 27 7 Signal Transduction Inducing Factor Families Retinoic acid can diffuse across the plasma membrane. Present in both vertebrates & invertebrates 1. Transforming growth factor β super family (TGF β). 2. Fibroblast growth factor family (FGFs). 3. Epidermal growth factor (EGF) 4. Hedgehog family 5. Wnt family Protein inducing factors cannot diffuse across the membrane – G-protein linked receptors Ion channel receptors Tyrosine kinase (main receptors) Activation of receptors activates a cascade and move to nucleus to activate target genes 29 Developmental Mechanisms PBL Amber just returned from New York and, she had felt sick the whole time, and the flu-like feeling still hadn't subsided. Question: What are three broad inter-related processes are involved in building an organism She was a little concerned, but attributed it mostly to nerves and lack of sleep. That night as she lay in bed reading, it felt like a gong was going off in her head. Maybe she was on edge over the recent break-up with her boy Answer: 1. Cell division 2. Cell differentiation 3. Morphogenesis 30 She went to sleep that night trying to ignore the unfamiliar pains and feelings that were consuming her. 31 32 8