2Developmental Biology Major QuestionsGrowth: regulation of sizeMorphogenesis: generation of ordered formDifferentiation: generation of cellular diversityReproduction: why and how is the germ line so specialEvolution: how do changes in development create new body formsEnvironmental integration: how does the environment influence developmentApproachesAnatomical : Comparative and Evolutionary Embryology, Teratology, ModelingExperimentalGenetic
3The Anatomical approach Anatomical approach : descriptive, based on the observation of morphological changesDiscovery of primary germ layers, inductive interactions amongst them.devbio8e-fig jpg
4Comparative embryology Aristotle in 350 B.C noticed that: 1) Animals are born in different ways: - oviparity: from eggs- viviparity: live birth - ovoviviparity: producing a egg that hatches inside the body2) Two major cell division patterns by which embryos are formed:- holoblastic pattern of cleavage: the entire egg is divided into smaller cells- meroblastic pattern of cleavage: only part of the egg is destined to become the embryo.
5Epigenesis and preformation In 1672, Marcello Malpighi published the first microscopic account of chick development.Debate: epigenesis X preformation - Epigenesis: organs of the embryo are formed from scratch- Preformation: organs of the embryo are already present in miniature formIn 1767, Kaspar Wolff proclaimed that he believed in the truth of epigenesis after working with chick embryos and seeing the heart and blood vessels to develop.The end of preformationism did not come until 1820s with Christian Pander, Karl Ernst von Baer, and Heinrich Rathke.
6Christian Pander- 1820sPander studied the chicken embryo and discovered the germ layers: - Ectoderm: generates the outer layer of the embryo. It produces the surface area (epidermis) of the skin abd forms of the brain and nervous system.- Mesoderm: generates the blood, heart, kidney, gonads, bones, muscles and connective tissue.- Endoderm: innermost layer of the embryo and produces the epithelium of the digestive tubes and its associated organs (including the lungs).Triploblastic- animals with 3 germ layersDiploblastic- animals with 2 germ layers
71.4 The notochord in the chick embryo Karl Ernst von Baer discovered the notochord and the mammalian egg.devbio8e-fig jpg
8Comparative / Evolutionary Embryology Von Baer rules: vertebrate embryos are very similar, sharing various structures. As they develop, they diverge. (pages 9 and 10)Darwin: community of embryonic structure reveals community of embryonic descent; comparison of embryonic forms help in establishing evolutionary relationshipsdevbio8e-fig jpg
91.6 Fate maps the early gastrula stage Cell lineage: following individual cells to see what they become.Techniques to follow normal development: FATE MAPPING (vital dye marking, radioactive or fluorescent labeling, genetic marking).devbio8e-fig jpg
101.7 Fate map of the tunicate embryo – Edwin Conklin, 1905 devbio8e-fig jpg
111.8 Vital dye staining of amphibian embryos devbio8e-fig jpg
121.9 Fate mapping using a fluorescent dye- zebrafish (Part 1) devbio8e-fig jpg
131.9 Fate mapping using a fluorescent dye- zebrafish (Part 2) devbio8e-fig jpg
141.10 Genetic markers as cell lineage tracers Chimeric embryos: graft of quail cells inside of a chicken embryo. Also called “mosaic” embryos.devbio8e-fig jpg
15The Cellular Basis of Morphogenesis Cells are constantly changing during embryogenesisMorphogenesis is brought about through a limited repertoire of variations in cellular processes within these two types of arrangements: - Direction and number of cell divisions - Cell shape changes - Cell movement - Cell growth- Cell death- Changes in the composition of the cell membrane or secreted productsCell migration: one of the most important contributions of fate maps has been their demonstration of extensive cell migration during development.
161.11 Neural crest cell migration (A) Mary Rawles (1940) showed that melanocytes of the chicken originate in the neural crest (NC).devbio8e-fig jpg(B)(C) Weston (1963) demonstrated that migrating NC cells gave rise to melanocytes, and peripheral neurons.
17Medical EmbryologyBetween 2 and 5% of live births show observable anatomical abnormalities.In the lack of experimental data…birth defects help us understand normal human development.Some birth defects are produced by mutant genes or chromosomal abnormalities, while others are produced by environmental factors.Genetic defects: malformations – often appear as syndromesUse of animal models to identify genetic, cellular and molecular basis of human syndromes.Ex: kit mutation leading to piebaldismEnvironmental defects: disruptionsResponsible agents: teratogens – chemicals, viruses, radiationEx: thalidomide leadind to phocomelia
181.15 Developmental anomalies caused by genetic mutation Piebaldism- dominant mutation on gene Kit. Includes anemia, sterility, unpigmented regions of the skin and hair, deafness, and absence of nerves that cause peristalsis in the gut.devbio8e-fig jpg
191.16 Developmental anomalies - environmental agent (Part 1) Disruptions: abnormalities caused by exogenous agents (certain chemicals or viruses, radiation, or hyperthermia).The agents responsible for these disruptions are called teratogens.1960s: increase of a previous rare syndrome of congenital abnormalities.Phocomelia caused by the drug thalidomide which were prescribed to pregnant women as a mild sedative.devbio8e-fig jpg
21Mathematical Modeling Base development on formal mathematical and physical principles.Mathematical modeling is strong in pattern formation and growth.Growth- Isometric: all components grow at the same rate, uniform (mollusk shells)- Allometric: components grow at different rates (human body)Patterning- Turing: reaction-diffusion model (tooth development)