Questions in developmental biology Differentiation Morphogenesis Growth/apoptosis Reproduction Evolution Environmental integration
Representative cell types of a vertebrate zygote => embryo => adult differentiation vs. determination progressive recognition of cell types (markers)
Malpighi, 1672 Chick embryo development Lillie, 1902 Pander, 1817 Carlson, 1981
Early gastrula Fate mapping: tracing cell lineages
Tunicate Styela partita Pigmented cytoplasmic regions => follow
Remove B4.1 => no tail muscle
Vital dye marking
Fluorescent dye caged => laser activation Zebrafish embryo Labels diluted after cell divisions
Antibody to a quail-specific protein Genetic markers nucleolus
Transplantation Pigmented => unpigmented (donor) (recipient, host) To the same location Neural crest cell migration
Cut and Paste: basic strategy to study development Tissues Genes Mark cells to trace???
Rules of Evidence (cause-effect) Correlative (temporal order) Loss-of-function Gain-of-function find it; lose it; move it Biology, like any other science, does not deal with Facts, but with evidence.
Animal model Piebaldism sterility, anemia, unpigmented regions in skin, deafness, defect in gut neurons dominant mutation in kit affects proliferation and migration of neural crest cells, germ cell precursors, bloood cell precursors
oocyte fertilization newly laid eggs Xenopus laevis
blastocoel Early blastula Late blastula
gastrulation Dorsal blastopore lip
Chick embryo
metamorphosis
Effect by environmental agents Thalidomide taken during pregnancy
Equiangular spiral growth
Allometric growth (different rates of growth)
Reaction-diffusion model
WT B-D: leopard mutants
Dictyostelium discoideum
camp
Cell adhesion molecules (CAM) gp24 induced after starvation gp80 streaming amoebae gp150 migrating slug
camp is required for prespore formation WT prespore-specific marker + camp-degrading enzyme cellulose (stalk cell wall) + DIF inducing prestalk cells
Major evolutionary divergence
Darwin: community of embryonic structures reveals community of descent barnacle crustacean, not mollusc shrimp Tunicate: larvae have notochords and formed neural tubes => chordate
Homologous structures (arise from common ancestral structure) Analogous structures (similar function, but not from a common ancestor) e.g bird wing and insect wing
Homologies of jaws and gill arches fish reptile mammal
Metazoans multicellular animals that pass through embryonic stages of development Diploblasts two germ layers (ectoderm, endoderm) Radiata: cnidarians, ctenophores radial symmetry Triploblasts three germ layers (ectoderm, endoderm, mesoderm) bilateral symmetry protostomes (mouth first, from blastopore) deuterostomes (mouth second; anus from blastopore)
von Baer s principles 1. The 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 are developed from the more general, until finally the most specialized appear 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 embryos of a higher animal is never like the lower animal, but only like its early embryo.
Amniote egg originated in reptiles water => land Similar invention in arthropods
Pharyngeal (branchial, gill) arches Salamader embryo; surface ectoderm removed
Chick embryo
Acetabularia Nuclear control of morphogenesis
Sexual reproduction in paramecium
Chlamydomonas
Meiosis
Volvocales Unicellular => multicellular species gonidia (germ cells)
Asexual reproduction in Volvox carteri 2 days cell movement resembling gastrulation
Bottle cells cell shape change => morphogenesis
somatic regenerator A blocked apoptosis somatic cells => gonidia
Sexual reproduction in Volvox carteri