Developmental Biology Biology 4361

Transcription

1 Developmental Biology Biology 4361 The Anatomical Tradition 2009

2 A hen is only an egg s way of making a new egg. Samuel Butler, 1885

3 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

4 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

5 Fundamental Questions & Concepts Gametes Life Cycle Adult gametes zygote embryo adult 1 cell 1 cell multiple (haploid) (diploid) cells ~10 11 cells 2 cell 1 cell multiple 200+ cell types type cell types types

6 General Questions (according to Gilbert) 1 cell (1 type) creates ~10 14 cells (~214 types) Yet, each cell in the zygote, embryo, and adult has identical DNA. 1. How do cells differentiate?

7 General Questions: Differentiated cells are organized into complex sets of tissues with a variety of functions. 2. How are cells organized into tissues and organs?

8 General Questions: During development, all cells, tissues, and organs naturally limit their growth. e.g. homeostasis each cell duplication must be matched by elimination of another cell - perfect waste management and recycling 1 Pathological conditions often tip this balance - stroke/infarction -AIDS - cancers 3. How do cells know when to stop dividing? 1. Galluzzi et al., 2007 Cell Death and Differentiation 14:

9 General Questions: Sperm and eggs are haploid and have many other cellular modifications that are necessary for reproduction. 4. How are gametes formed?

10 General Questions: New phenotypes have the potential to be established only during an organism s developmental l period. 5. How do changes in development create new body forms?

11 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?

12 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 g 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 t of its habitat? t? [Environmental integration]

13 Scientific Approaches Comparative embryology (historic) Experimental embryology (modern) Evolutionary embryology Teratology Mathematical modeling

14 Comparative Embryology Dr. Nicole Valenzuela Richard N Feinberg, Greg Holmes

15 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) - microscopic account of development

16 Origins Preformation v. Epigenesis Preformation new organism contained in sperm or egg - no cell theory y( (no size problem) - age of Earth unknown (so not a problem) - eliminated need for vital force Homunculus Epigenesis new organism formed de novo ( from scratch ) epi - after genesis - origin i - explained mixture of traits in hybrids -explained blending of traits - embryos had structures unknown in adults

17 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) - microscopic account of development Kaspar Friedrich Wolff ( ) - differentiated tissues arise from undifferentiated cells Christian Pander (c. 1817) - germ layers, induction

18 Germ Layers Germ layer region of cells that give rise to all tissues and organs germ initiates development or serves as an origin ecto- outside, external endo- inside, id internal, within meso- middle, intermediate -dermd skin, covering -blast immature form

19 Germ Layers Diploblastic organisms (cnidaria, ctenophores, porifera) - 2 germ layers (lack true middle layer) Triploblastic organisms (vertebrates, echinoderms, etc) - 3 germ layers

20 Germ Layers Diploblastic organisms (cnidaria, ctenophores, porifera) - 2 germ layers (lack true middle layer) Triploblastic organisms (vertebrates, echinoderms, etc) - 3 germ layers Ectoderm Mesoderm Endoderm - outer layer; forms epidermis, brain, CNS - - middle layer; forms blood, heart, kidneys, gonads, bones, muscles, connective tissues inner layer; forms inside of digestive tract, associated organs

21 Triploblasts Diploblasts

22 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) - microscopic account of development Kaspar Friedrich Wolff ( ) - differentiated tissues arise from undifferentiated cells Christian Pander (c. 1817) - germ layers, induction Karl Ernst von Baer (1820 s) - described blastula, notochord, mammalian egg

23 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. B k k d th t iti f i l von Baer s work marked the transition from mainly observational to experimental embryology.

24 Scientific Approaches Comparative embryology (historic) Experimental embryology (modern techniques) Embryo manipulation Cell lineage Fate mapping Evolutionary embryology Teratology Mathematical modeling

25 Experimental Embryology Techniques Isolation remove and grow part of embryo by itself (no communication, signals, regulation from outside) Removal a portion of the embryo is removed What happens to the remaining i embryo? Is there a gap? Are organs or tissues missing? Transplantation portion removed, transplanted to another embryo homospecific - same species heterospecific - different species heterochronic h - different age heterotopic - different place (same embryo)

26 Tracing Cell Lineage C. elegans invariant cell lineages cells; each lineage known

27 Constructing Fate Maps zygote 8-cell

28 Fate Mapping

29 Fate Mapping Techniques Heterospecific transplantation

30 Scientific Approaches Comparative embryology (historic) Experimental embryology (modern) Evolutionary embryology Teratology Mathematical modeling

31 Evolutionary Embryology Homologous structures? Analogous structures?

32 Homologous Structures

33 Evolutionary Embryology jointed legs, etc. barnacle larvae barnacle (arthropod) notochord, nerve cord sea squirt larvae sea squirt (chordate)

34 Evolutionary Developmental Biology Peripatus Distal-less gene

35

36 Scientific Approaches Comparative embryology (historic) Experimental embryology (modern) Evolutionary embryology Teratology/medical embryology Mathematical modeling

37 Medical Embryology & Teratology

38 Mathematical Embryology

39 Mathematical Embryology Mort Henick