Developmental Anatomy

1. Developmental Anatomy • PreformationvsEpigenesis: A history. • Primary Germ Layers and early organs. • Karl von Baer and his laws. • Fate Mapping • Evolutionary Embryology.

2. Aristotle: First biologist? • The Generation of Animals (350 BCE) • Noted Variations of life cycle themes: • Some born of Eggs (oviparity) • Some from live birth (viviparity) • Some from eggs, but hatch in mother (ovoviviparity). • Holoblastic- whole egg divided into smaller cells • Meroblastic- half egg divides into smaller cells; rest is yolk sac.

3. Cell Division differs amongst species

4. Ex ovoomnia- Willaim Harvey 1651

5. Preformation • Belief that everything is in egg and/or sperm in smaller form. • Overtime, organs and essentially the organism grows. • Marcello Malphigi- studies chick embryos..notes abundance of structure in embryo and questions epigenesis • Predates cell theory

6. Epigenesis • Embryonic parts arise from embryonic tissue. Newly formed organs. • Kasper Friedrich Wolff provides evidence that embryonic organs arise from tissue that has no adult counter part! • Sets the foundation for Germ layer theory.

7. “Developmental Force” • Immanuel Kant and Johann Friedrich Blumenbach (mid to late 1700s). • Mystical force leads to development of embryos. • This “force” is heritable from germ cells and highly susceptible to change. • Mendel’s work almost a century later… • Developmental force= Genetics?

8. Using the microscope revolutionizes development • Christian Pander, Heinrich Rathke, and Karl Ernst von Baer. • Identify the three germ layers: • Ectoderm • Mesoderm • Endoderm

9. The Three Germ Layers

10. Triploblastic and diploblastic Organisms • These organisms use all three germ layers. • Some organisms only use two germ layers (lack mesoderm): • Porifera (sponges) • Cnidarians (sea anemones, hydra, jellyfish) • Ctenophores (comb jellies)

11. Axes and Symmetry

12. Christian Pander • Work with Chick Embryos. • Supports epigenesis by showing that tissues worked together to form organs. • Discovers tissue interaction-Induction: • No tissue can form organs alone, must interact with other tissues in order to for organogenesis to occur.

13. Heinrich Rathke • Discovered pharyngeal arches. • In fish, these arches give rise to gill apparatus • In humans, form jaw, ears, vertebrate skull.

14. Karl Ernst von Baer • “Father” of Developmental Biology • Expanded Pander’s studies of Chick Embryos. • Identifies notochord- rod of dorsal-most mesoderm tissue. • Notochord divides embryo in right and left sides, instructs ectoderm above it to differentiate into nerve tissue.

15. von Baer laws • Rule 1: The general features of a large group of animals appear earlier in development than do the specialized features of a smaller group. • All vertebrates have similar structures during development: gill arches, notochord, primitive kidneys. • Very similar shortly after gastrulation.

16. von Baer’s laws • Rule 2: Less General characters are developed from the more general, until finally the most specialized appear. • All vertebrates have skin, later skin becomes feathers for birds, scales for reptiles, hair and nails for mammals

17. von Baer’s Laws • Rule 3: The embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them. • Visceral clefts of embryonic birds/mammals do not ressemble gill slits of adult fish.

18. von Baer’s Laws • Rule 4: Therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo. • We never pass through a developmental stage similar to adult fish or birds.

19. Are there really similarities?

20. The Cell theory and Fate mapping • Matthias Schleiden and Theodor Schwann in 1838 formalize the Cell theory: all living organisms are composed of cells! • Embryologists followed this movement and began tracking cell movement during development!

21. Two Cell types: Epithelial and Mesenchymal • Epithelial • Mesenchymal

22. Morphogenesis • Direction and No. of cell divisions • Cell shape changes • Cell movement • Cell growth • Cell death.

23. Cell Movement and association Cadherin based adhesion-self association. Different strength of interaction

24. Morphogenesis

25. How do you fate map cells? • Observing live embryos! • Edwin G Conklin • Still used as primary fate mapping technique. • Zebra Fish will allow you to do this!

26. How do you fate map cells? • Vital Dye Marking • Vital dyes stain the cells but don’t kill them. • Dead cells tell no tales…unless you study apoptosis.

27. How do you fate map cells? • Radioactive/ Fluorescent labeling • Radioactive label: Transplant of graft from radiolabeled embryo to unlabeled embryo. Silver stain! • Fluorescent labeling: Inject fluorescent dye into cells of embryo.

28. How do you fate map cells? • Genetics! • Use cells from another organism that contain a easily detectable marker!

29. Darwin: Embryology’s biggest fan! • Saw Embryology as support for his theories. • “Community of embryonic structure reveals community of descent” • This is shown in Homologous structures, such as the forelimb of human arms vs. wings of a bird! • What would be an analogous structure?

30. Evolutionary change is due to developmental change.. • Ontogeny causes phylogeny? • Human fingers versus Bat wing!