Part I Chapter 1
-Basic Problems of developmental Biology:
• Maintenance of complete genome while cells differentiate
-Main mechanisms of differential gene expression-polarity and cytoplasmic differences; polarity: • Gene expression leads to a difference in cells
• Every cell in body has the same genome
• Gene regulation occurs:
o Polarity and cell division
▪ Uneven egg contents
▪ Environmental factors
o Gene cascades
▪ Cell-cell signaling
-What does development encompass?
• Development begins at fertilization
• Study of the emergence of living order
-What are the basic questions in developmental biology?
1. Question of differentiation-how can identical genetic instructions produce different types of cells? How can single cell generate so many cells? 2. Question of morphogenesis-how can cells in body organize into functional structures? 3. Question of growth-how do cells know to stop dividing? 4. Question of reproduction-how are germ cells set apart from somatic cells? What instructions are in the nucleus and cytoplasm? 5. Question of regeneration-how do stem cells retain regeneration capacity? Can we harness it to cure diseases? 6. Question of evolution-how do changes in development create new body forms? 7. Question of environmental integration-can environmental chemicals disrupt development? How is development of organism integrated into its habitat?
-Some basics: similarity and relatedness of organisms; development of 3 germ layers: • All develop three germ layers:
o Ectoderm- skin, nervous system, brain and nervous system o Endoderm- gut, digestive tract and associated organs, the lungs o Mesoderm- all the rest, kidney blood, heart, gonads, bones, muscles
-History of Embryology-Von Baer’s principles and Haeckel’s misinterpretation; fate mapping and cell lineages: • Von Baer’s Principles:
1. General features appear earlier in development than specialized features 2. Less general characters develop from the more general; until finally the most specialized appear. (originally have same skin, later skin develops) 3. The embryo 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. • Haekel misinterpretated: thought he was talking about recapitulation. (The idea that embryonic development repeats that of one’s ancestors.) o He implied that we go through a fishlike stage
▪ We don’t
▪ However, development (ontogeny) and evolutionary relationships (phylogeny) are related. • Fate maps and cell lineages:
o Vital dye marking
o Transplantation of labeled cells
o Injection of tracers into cells
o Chimeras (such as chick-quail)
• Some cells are highly migratory
-What are the basic cellular processes (ingression, epiboly, etc)? • Ingression-migration of individual cells form surface into the interior of the embryo. • Invagination-infolding of a region of cells much like the indenting of a rubber ball when poked. • Involution-inturning or inward movement of an expanding outer layer so that it spreads over the internal surface of the remaining external cells. • Delamination-the splitting of one cellular sheet into two more less parallel sheets. • Epiboly-the movement of epithelial sheets that spread as a unit to enclose the deeper layers of the embryo.
-Homology vs Analogy:
• Homology=similarity via common ancestry (wing of a bird, arm of a human) • Analogy=via common function (wing of bird and wing of butterfly)
-Basic stages of development:
1. Fertilization-fusion of sex cells
2. Cleavage-mitotic divisions
3. Gastrulation-blastomre moves and causes changes in position...