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BIOL 230-Development-Case A Body-Building Plan Ontogeny recapitulates phylogeny (sort of) Ontogeny recapitulates phylogeny (sort of) A human embryo at about 7 weeks after conception shows development of distinctive features EMBRYONIC DEVELOPMENT Sperm Zygote Egg Larval stages ESIS GEN ANO ORG Metamorphosis GE VA EA CL GA ST RU LA TIO N Fertilization and cleavage initiate embryonic development Fertilization is the formation of a (1)___ploid zygote from a (2)___ploid egg and sperm FER TIL IZA TIO N Adult frog Basal body (centriole) Sperm head Blastula Acrosome Jelly coat Sperm-binding receptors Gastrula Vitelline layer Egg plasma membrane Tail-bud embryo Sperm plasma membrane Sperm nucleus Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Basal body (centriole) Sperm head Hydrolytic enzymes Vitelline layer Egg plasma membrane Acrosome Jelly coat Sperm-binding receptors Acrosomal process Actin filament Hydrolytic enzymes Vitelline layer Egg plasma membrane Sperm nucleus Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Acrosomal process Actin filament Fused plasma membranes Hydrolytic enzymes Vitelline layer Egg plasma membrane BIOL 230-Development-Case Experiment Fertilization envelope Egg Activation Sperm plasma membrane Sperm nucleus Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors The rise in Ca2+ in the cytosol increases the rates of cellular respiration and protein synthesis by the egg cell Fertilization envelope Acrosomal process 10 sec after fertilization Actin filament Cortical Fused granule plasma membranes Perivitelline Hydrolytic enzymes space Vitelline layer EGG CYTOPLASM Egg plasma membrane 25 sec Results Point of sperm nucleus entry 35 sec 1 min 500 µm (3) From where does the Ca2+ come? (4) What would happen if you injected a sea urchin egg with Ca2+? Spreading wave of Ca2+ (5) Does MPF remain constant in an embryo? 1 sec before fertilization 10 sec after fertilization 20 sec 30 sec From where does the egg get the necessary proteins and mRNA? 500 µm Cleavage Fertilization is followed by cleavage, which is (6) _____ 50 µm 50 µm Which are you? Which are you? (7) Protostome 50 µm Deuterostome BIOL 230-Development-Case Zygote Animal hemisphere Cleavage furrow Cleavage Pattern in Frogs In frogs and many other land animals, cleavage is asymmetric due to the distribution of yolk 0.25 mm Vegetal hemisphere Gray crescent Animal pole 2-cell stage forming Zygote Animal hemisphere Cleavage furrow 0.25 mm Vegetal hemisphere Gray crescent 4-cell stage forming Animal pole 0.25 mm 8-cell stage Blastocoel 2-cell stage forming 4-cell stage forming 8-cell stage Blastula (cross section) Cleavage Patterns Contrast the two embryos: (8) Morphogenesis Morphogenesis Cleavage Patterns Holoblastic cleavage Morphogensis Morphogenesis Gastrulation Organogenesis Cleavage Patterns Meroblastic cleavage Organogenesis During organogenesis, various regions of the germ layers develop into rudimentary organs Adoption of particular developmental fates may cause cells to change shape or even migrate to a new location in the body BIOL 230-Development-Case Characteristics of the phylum chordata ___ Neurulation Neural folds Eye Neural fold Somites Tail bud Neural plate Neurulation begins as cells from the dorsal mesoderm form the notochord (9) ___ Signaling molecules secreted by the notochord and other (10)_____dermal cells cause the ectoderm above to form the neural plate ___ This is an example of (11)_____ SEM 1 mm Neural Neural fold plate Notochord Ectoderm Mesoderm Neural tube Neural crest cells Endoderm Archenteron Notochord Coelom Neural crest cells Archenteron (digestive cavity) Outer layer of ectoderm Neural tube (a) Neural plate formation Neural fold Neural plate Neural fold Neural plate (b) Neural tube formation Neural fold Neural crest cells Neural crest cells (b) Neural tube formation Neural fold Neural plate (b) Neural tube formation Eye Somites (c) Somites Neural plate Neural crest cells Outer layer of ectoderm Neural tube (b) Neural tube formation Tail bud Eye Forebrain Heart Neural crest cells Neural crest cells Outer layer of ectoderm Neural tube (b) Neural tube formation SEM Neural tube Notochord Coelom Blood vessels 1 mm Neural crest cells Somite Somites Neural tube (b) Late organogenesis 1 mm Neural crest cells Somite BIOL 230-Development-Case Mechanisms of Morphogenesis Mechanisms of Morphogenesis movement of cells Ectoderm Neural plate Microtubules cytoskeleton Convergence Cells elongate and crawl between each other. Actin filaments Extension The sheet of cells becomes longer and narrower. What would happen if you treated an embryo with vinblastine just before neural tube development? (12) Ectoderm Programmed Cell Death Neural plate Microtubules Many more neurons are produced in developing embryos than will be needed In some cases a structure functions in early stages and is eliminated during later development What happens to the extras? (13) What happens to the tadpoles tail? (14) Actin filaments Neural tube Fate Mapping Determination is the term used to describe the process by which a cell or group of cells becomes committed to a particular fate Differentiation refers to the resulting specialization in structure and function Cells in a multicellular organism share the same genome So how do you have different cells? (15) Fate maps are _____ BIOL 230-Development-Case Fate Mapping Fate maps are diagrams showing organs and other structures that arise from each region of an embryo Studies of Caenorhabditis elegans used ____ 100,291,840 bp 19,735 protein-coding genes Studies of Caenorhabditis elegans used gene deletion 100,291,840 bp 19,735 protein-coding genes Axis Formation 20 µm Bilateral Radial 100 µm 1 Newly fertilized egg 3 Two-cell embryo 2 Zygote prior to first division 4 Four-cell embryo Cells with P granules Restricting Developmental Potential The anterior-posterior axis of the frog embryo is determined during oogenesis The first two cells of the frog embryo are totipotent, meaning (18) ____ Experiment Control egg (dorsal view) Experimental egg (side view) Control group Gray crescent Experimental group Gray crescent What determines the A-P axis? (16) The dorsal-ventral axis is not determined until fertilization What determine the D-V axis? (17) Thread BIOL 230-Development-Case Experiment Control egg (dorsal view) Experimental egg (side view) Control group Experimental group Gray crescent Gray crescent The “Organizer” of Spemann and Mangold Spemann and Mangold transplanted tissues between early gastrulas … Experiment Results Dorsal lip of blastopore Primary embryo Secondary (induced) embryo Pigmented gastrula (donor embryo) Thread Neural tube Notochord Nonpigmented gastrula (recipient embryo) Notochord (pigmented cells) Neural tube (mostly nonpigmented cells) Results Why did this happen happened? (19) Normal Belly piece Normal The “Organizer” of Spemann and Mangold Formation of the Vertebrate Limb …the transplanted dorsal lip of the blastopore triggered a second gastrulation in the host Inductive signals play a major role in pattern formation, development of spatial organization The dorsal lip functions as an organizer of the embryo body plan, inducing changes in surrounding tissues to form notochord, neural tube, and so on The molecular cues that control pattern formation are called positional information Anterior Limb bud 2 AER Digits ZPA Limb buds 50 µ m Posterior Anterior Apical ectodermal ridge (AER) 3 4 Ventral Proximal Distal Dorsal Posterior (a) Organizer regions (b) Wing of chick embryo Anterior Limb bud AER Limb buds ZPA Posterior 50 µm Apical ectodermal ridge (AER) 50 µm Apical ectodermal ridge (AER) Zone of polarizing activity (ZPA) The ZPA influences development by secreting a protein signal called Sonic hedgehog What happens if cells expressing Sonic hedgehog are implanted into the ZPA site of a normal limb bud? (20) BIOL 230-Development-Case Experiment Sonic hedgehog: What’s in a name? Anterior Sonic hedgehog: What’s in a name? New ZPA Donor limb bud Host limb bud ZPA 1993 Nobel prize: Christiane Nusslein-Volhard Eric Wieschausspiky Posterior Results 1993 Nobel prize: Christiane NussleinVolhard Eric Wieschausspiky Protein looked like a hedgehog 4 3 2 2 4 3 Sonic hedgehog: What’s in a name? Sonic hedgehog: What’s in a name? 1993 Nobel prize: Christiane Nusslein-Volhard Eric Wieschausspiky 1993 Nobel prize: Christiane Nusslein-Volhard Eric Wieschausspiky Protein looked like a hedgehog Protein looked like a hedgehog Other hedgehog genes: Other hedgehog genes: Indian Indian Dessert Dessert …So why Sonic? …So why Sonic? S S G1 M G2 M Cell cycle during cleavage stage Cell cycle after cleavage stage So how does a cell know when to stop? (21) Development answers How does this happen? (22) 1. 2. diploid haploid 3. 4. ER A fertilization membrane would form and fertilization would be prevented No, it should fluctuate mitosis + cytokinesis 5. 6. 7. 8. 9. deuterostome top one is complete cleavage notochord, hollow dorsal nerve cord, pharyngeal gill slits 10. mesodermal 11. Induction 12. cytoskeleton wouldn’t rearrange so no neural tube 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. apoptosis apoptosis expression of different genes animal-vegetal poles sperm entry can develop into any tissue The dorsal lip of the blastopore induced cells in another part of the amphibian embryo to change their developmental fate A mirror image limb results Cleavage-clock-regulated: Evidence suggests that the 60-cell stage, just prior to gastrulation, is the time of zygotic gene activation A developing embryo begins to split into identical twins but then stops part way, leaving the twins joined.
