Download 1. The Anatomical Tradition

Developmental Biology – Biology 4361 The Anatomical Tradition June 10, 2008
A hen is only an egg’s way of making a new egg. Samuel Butler, 1885
The Anatomical Tradition ­ Overview What is developmental biology? How do biologists study it? Fundamental concepts and questions General questions Scientific approaches Historical Modern
Core concepts Fundamental Questions & Concepts How does a fertilized egg give rise to the adult body? How does the adult body produce yet another body? Gametes Life Cycle Adult gametes zygote embryo adult 1 cell (haploid) 1 cell (diploid) multiple cells ~10 11 cells 2 cell types 1 cell type multiple cell types 200+ cell types
General Questions of Developmental Biology* Humans: 1 cell (1 type) creates ~10 14 cells (~214 types). Each cell (zygote, embryo, and adult) has identical DNA.
1. How do cells differentiate? *According to Gilbert General Questions: Differentiated cells are organized into complex sets with a variety of functions.
2. How are cell organized into tissues and organs? General Questions: During development, all cells, tissues, and organs naturally limit their growth. 3. How do cells know when to stop dividing? “Think about homeostasis (in the adult); each event of cell duplication must be compensated by the elimination of another cell. This requires extremely tight regulation of cell death, along with “perfect waste management” and recycling.” “Pathological conditions often tip this balance; e.g. disregulated cell cycle (e.g. mitosis) and cell death (either excessive or diminished. e.g. stroke or infarction lead to excess cell death in neurons and cardiomyocytes, respectively. AIDS caused by loss of proliferating immune cells at a pace greater than they can be replaced. Cancers characterized in part by suppression of cell death programs (which lead to chemo­ and radio­therapy resistance, thus eventually causing somatic death.” Galluzzi et al., 2007 Cell Death and Differentiation 14:1237­1266
General Questions: Sperm and eggs are haploid and have many other cellular modifications that are necessary for reproduction.
4. How is gametogenesis accomplished? General Questions: New phenotypes have the potential to be established only during an organism’s developmental period.
5. How do changes in development create new body forms? General Questions: During development organisms respond to the environmental conditions to which they are exposed.
6. How is development of an organism integrated into the larger context of its habitat? General Questions: 1. How do cells differentiate? [Differentiation] 2. How are cells organized into tissues and organs? [Morphogenesis] 3. How do cells know when to stop dividing? [Growth] 4. How is gametogenesis accomplished? [Reproduction] 5. How do changes in development create new body forms? [Evolution] 6. How is development of an organism integrated into the larger context of its habitat? [Environmental integration]
Scientific Approaches Comparative embryology (historic) Experimental embryology (modern) Evolutionary embryology Teratology Mathematical modeling
Scientific Approaches Comparative embryology (historic) Historical roots Preformation v. epigenesis Germ line Germ layers
Experimental embryology (modern) Evolutionary embryology Teratology Mathematical modeling Comparative Embryology Dr. Nicole Valenzuela
Richard N Feinberg, Greg Holmes Comparative Embryology Hippocrates (5 th century BCE) ­ recognized development Aristotle (4 th century BCE) ­ cleavage patterns, viviparity, etc.* William Harvey (1640s) ­ Ex ovo omnia (“all from the egg”) Marcello Malpighi (1672) ­ 1st microscopic account of chick development
Origins – Preformation v. Epigenesis Preformation – new organism contained in sperm or egg ­ no cell theory to constrain size ­ age of Earth unknown (so not a problem) ­ eliminated need for “vital force” Homunculus Epigenesis – new organism formed de novo (“from scratch”) epi­ “after” (or upon, over, besides, outer, attached to) genesis ­ “origin” (or coming into being of something)
­ explained mixture of traits in hybrids ­ explained blending of traits ­ embryos had structures unknown in adults Comparative Embryology Hippocrates (5 th century BCE) ­ recognized development Aristotle (4 th century BCE) ­ cleavage patterns, viviparity, etc.* William Harvey (1640s) ­ Ex ovo omnia (“all from the egg”) Marcello Malpighi (1672) ­ 1st microscopic account of chick development Kaspar Friedrich Wolff (1733­1794) ­ differentiated tissues arise from undifferentiated cells Christian Pander (c. 1817) ­ germ layers, induction
Germ Line Concept Soma = somatic cells = all but gametes soma
continuous germ line Germ Line Concept Soma = somatic cells = all but gametes
Germ Line Concept Soma = somatic cells = all but gametes
Germ Layers germ – initiates development or serves as an origin ecto­ outside, external endo­ inside, internal, within meso­ middle, intermediate ­derm skin, covering blast – formative unit, esp. of living matter, bud, budding, or germ Germ Layers Ectoderm ­ outer layer; forms epidermis (skin), brain, CNS Mesoderm ­ middle layer; forms blood, heart, kidneys, gonads, bones, muscles, connective tissues Endoderm ­ inner layer; forms inside of digestive tract, associated organs Triploblastic organisms (vertebrates, echinoderms, etc) ­ 3 germ layers Diploblasts (cnidaria, ctenophores, porifera) lack true mesoderm
Comparative Embryology Hippocrates (5 th century BCE) ­ recognized development Aristotle (4 th century BCE) ­ cleavage patterns, viviparity, etc.* William Harvey (1640s) ­ Ex ovo omnia (“all from the egg”) Marcello Malpighi (1672) ­ 1st microscopic account of chick development Kaspar Friedrich Wolff (1733­1794) ­ differentiated tissues arise from undifferentiated cells Christian Pander (c. 1817) ­ germ layers, induction Heinrich Rathke (1820’s) ­ similarity between species Karl Ernst von Baer (1820’s) ­ described blastula, notochord, mammalian egg; established “von Baer’s laws”
von Baer’s Laws 1. General features of a large group of animals appear earlier in development than do the specialized features of a smaller group. 2. Less general characters develop from the more general, until finally the most specialized appear. 3. The embryos of a given species, instead of passing through the adult stages of lower animals, departs more and more from them. 4. Therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo. von Baer’s work marked the transition from mainly observational to experimental embryology.
Scientific Approaches Comparative embryology (historic) Experimental embryology (modern techniques) Embryo manipulation Cell lineage Fate mapping
Evolutionary embryology Teratology Mathematical modeling Experimental Embryology Techniques Isolation – remove and grow part of embryo by itself (no communication, signals, regulation from outside) How do the cells/tissues respond? Removal – a portion of the embryo is removed What happens to the remaining embryo? Is there a gap? Are organs or tissues missing? Transplantation – portion removed, transplanted to another embryo Same species = homospecific Different species = heterospecific Different age = heterochronic Different place (same embryo) = heterotopic How does the transplanted tissue respond?
Tracing Cell Lineage Ceanorhabditis elegans invariant cell lineages ­ 959 cells; each lineage known
Constructing Fate Maps
zygote 8­cell Fate Mapping
Fate Mapping Techniques Heterospecific transplantation
Scientific Approaches Comparative embryology (historic) Experimental embryology (modern) Evolutionary embryology Teratology Mathematical modeling
Evolutionary Embryology Homologous structures? Analogous structures?
Homologous Structures
Evolutionary Embryology jointed legs etc. barnacle larvae barnacle (arthropod) notochord, nerve cord
sea squirt larvae sea squirt (chordate) Evolutionary Developmental Biology Peripatus Distal­less gene
Scientific Approaches Comparative embryology (historic) Experimental embryology (modern) Evolutionary embryology Teratology/medical embryology Mathematical modeling
Medical Embryology & Teratology
Mathematical Embryology
Mathematical Embryology