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The most complex problem How to get from here The most complex problem How to get from here to there LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 47 Animal Development Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Figure 47.1 A human embryo at about 7 weeks after conception shows development of distinctive features 1 mm Development: cellular level • Cell division • Differentiation – cells become specialized in structure & function • Morphogenesis (organogenesis) Development: cellular level • Cell division • Differentiation – cells become specialized in structure & function • if each kind of cell has the same genes, how can they be so different? – shutting off of genes = loss of totipotency – Turning genes on based on chemical cues • Morphogenesis (organogenesis) Development: cellular level • Cell division • Differentiation – cells become specialized in structure & function • if each kind of cell has the same genes, how can they be so different? – shutting off of genes = loss of totipotency – Turning genes on based on chemical cues • Morphogenesis (organogenesis) – “creation of form” = give organism shape – basic body plan • polarity – one end is different than the other • symmetry – left & right side of body mirror each other • asymmetry – look at your hand… Our model organisms Developmental events EMBRYONIC DEVELOPMENT Sperm Zygote Adult frog Egg Metamorphosis Blastula Larval stages Gastrula Tail-bud embryo Fertilization in sea urchins: fast block and slow block to polyspermy Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Vitelline layer Egg plasma membrane Figure 47.3-2 Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Hydrolytic enzymes Vitelline layer Egg plasma membrane Figure 47.3-3 Sperm nucleus Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Acrosomal process Actin filament Hydrolytic enzymes Vitelline layer Egg plasma membrane Figure 47.3-4 Sperm 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 Figure 47.3-5 Sperm plasma membrane Sperm nucleus Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Fertilization envelope Acrosomal process Actin filament Cortical Fused granule plasma membranes Hydrolytic enzymes Perivitelline space Vitelline layer Egg plasma membrane EGG CYTOPLASM EXPERIMENT 10 sec after fertilization Slow block RESULTS to polysperm y: Change in Ca++ in the egg makes f.e. 1 sec before fertilization 25 sec 35 sec 1 min 10 sec after fertilization 20 sec 30 sec CONCLUSION Point of sperm nucleus entry Spreading wave of Ca2 Fertilization envelope 500 m 500 m Egg Activation • The rise in Ca2+ in the cytosol increases the rates of cellular respiration and protein synthesis by the egg cell • With these rapid changes in metabolism, the egg is said to be activated • The proteins and mRNAs needed for activation are already present in the egg • The sperm nucleus merges with the egg nucleus and cell division begins © 2011 Pearson Education, Inc. • When the sperm binds a receptor in the zona pellucida, it triggers a slow block to polyspermy (no fast block to polyspermy has been identified in mammals) Zona pellucida Follicle cell Sperm basal body Sperm nucleus Cortical granules CLEAVAGE •Fertilization is followed by cleavage, a period of rapid cell division without growth •Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres •The blastula is a ball of cells with a fluid-filled cavity called a blastocoel 50 m (a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula Cleavage in a frog embryo Zygote 2-cell stage forming Gray crescent 0.25 mm 8-cell stage (viewed from the animal pole) 4-cell stage forming 8-cell stage Animal pole 0.25 mm Blastula (at least 128 cells) Vegetal pole Blastula (cross section) Blastocoel Concept 47.2: Morphogenesis in animals involves specific changes in cell shape, position, and survival • Morphogenesis, the process by which cells occupy their appropriate locations, involves – Gastrulation, the movement of cells from the blastula surface to the interior of the embryo – Organogenesis, the formation of organs © 2011 Pearson Education, Inc. Figure 47.8 ECTODERM (outer layer of embryo) • Epidermis of skin and its derivatives (including sweat glands, hair follicles) • Nervous and sensory systems • Pituitary gland, adrenal medulla • Jaws and teeth • Germ cells MESODERM (middle layer of embryo) • Skeletal and muscular systems • Circulatory and lymphatic systems • Excretory and reproductive systems (except germ cells) • Dermis of skin • Adrenal cortex ENDODERM (inner layer of embryo) • Epithelial lining of digestive tract and associated organs (liver, pancreas) • Epithelial lining of respiratory, excretory, and reproductive tracts and ducts • Thymus, thyroid, and parathyroid glands Gastrulation in the sea urchin Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Blastocoel Filopodia Mesenchyme cells Blastopore Archenteron 50 m Blastocoel Ectoderm Key Future ectoderm Future mesoderm Future endoderm Mouth Mesenchyme (mesoderm forms future skeleton) Archenteron Blastopore Digestive tube (endoderm) Anus (from blastopore) Gastrulation in frog embryo 1 CROSS SECTION SURFACE VIEW Animal pole Blastocoel Dorsal lip of blastopore Early Vegetal pole gastrula Blastopore Blastocoel shrinking 2 3 Blastocoel remnant Dorsal lip of blastopore Archenteron Ectoderm Mesoderm Endoderm Key Future ectoderm Future mesoderm Future endoderm Late gastrula Blastopore Blastopore Yolk plug Archenteron Gastrulation in chicks Fertilized egg Primitive streak Embryo Yolk Primitive streak Epiblast Future ectoderm Blastocoel Migrating cells (mesoderm) Endoderm Hypoblast YOLK 1 Blastocyst reaches uterus. Uterus Embryonic development in humans Endometrial epithelium (uterine lining) Inner cell mass Trophoblast Blastocoel 2 Blastocyst implants (7 days after fertilization). Expanding region of trophoblast Maternal blood vessel Epiblast Hypoblast Trophoblast 3 Extraembryonic membranes start to form (10–11 days), and gastrulation begins (13 days). Expanding region of trophoblast Amniotic cavity Epiblast Hypoblast Yolk sac (from hypoblast) Extraembryonic mesoderm cells (from epiblast) Chorion (from trophoblast) 4 Gastrulation has produced a three-layered embryo with four extraembryonic membranes. Amnion Chorion Ectoderm Mesoderm Endoderm Yolk sac Extraembryonic mesoderm Allantois Figure 47.12a Endometrial epithelium (uterine lining) Uterus Inner cell mass Trophoblast Blastocoel 1 Blastocyst reaches uterus. Figure 47.12b Expanding region of trophoblast Maternal blood vessel Epiblast Hypoblast Trophoblast 2 Blastocyst implants (7 days after fertilization). Figure 47.12c Expanding region of trophoblast Amniotic cavity Epiblast Hypoblast Yolk sac (from hypoblast) Extraembryonic mesoderm cells (from epiblast) Chorion (from trophoblast) 3 Extraembryonic membranes start to form (10–11 days), and gastrulation begins (13 days). Figure 47.12d Amnion Chorion Ectoderm Mesoderm Endoderm Yolk sac Extraembryonic mesoderm Allantois 4 Gastrulation has produced a three-layered embryo with four extraembryonic membranes. Developmental Adaptations of Amniotes • The colonization of land by vertebrates was made possible only after the evolution of 1. The shelled egg of birds and other reptiles as well as monotremes (egg-laying mammals) 2. The uterus of marsupial and eutherian mammals © 2011 Pearson Education, Inc. • The four extraembryonic membranes that form around the embryo in a reptile/bird: – – – – The chorion functions in gas exchange The amnion encloses the amniotic fluid The yolk sac encloses the yolk The allantois disposes of waste products and contributes to gas exchange © 2011 Pearson Education, Inc. Neuralation in a frog embryo Eye Neural folds Neural fold Tail bud Neural plate SEM 1 mm Neural fold Somites Neural tube Neural plate Notochord Neural crest cells 1 mm Neural crest cells Coelom Notochord Somite Ectoderm Mesoderm Endoderm Neural crest cells Outer layer of ectoderm Archenteron (a) Neural plate formation Neural tube (b) Neural tube formation Archenteron (digestive cavity) (c) Somites Organogenisis in a chick Neural tube Notochord Eye Forebrain Somite Coelom Endoderm Mesoderm Ectoderm Archenteron Lateral fold Heart Blood vessels Somites Yolk stalk These layers form extraembryonic membranes. (a) Early organogenesis Yolk sac Neural tube YOLK (b) Late organogenesis Ectoderm Morphogenesis results from cells changing shape Figure 47.15-2 Ectoderm Neural plate Microtubules Figure 47.15-3 Ectoderm Neural plate Microtubules Actin filaments Figure 47.15-4 Ectoderm Neural plate Microtubules Actin filaments Figure 47.15-5 Ectoderm Neural plate Microtubules Actin filaments Neural tube Elongation of tissue by convergent extension Concept 47.3: What determines how parts form; and messing with those determining factors • 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 – Can result from: oocyte composition, logal signals, gravity © 2011 Pearson Education, Inc. Epidermis Fate mapping Central nervous system Notochord Epidermis Mesoderm Endoderm Blastula Neural tube stage (transverse section) (a) Fate map of a frog embryo 64-cell embryos Blastomeres injected with dye Larvae (b) Cell lineage analysis in a tunicate Time after fertilization (hours) Figure 47.18 Zygote 0 First cell division Nervous system, outer skin, musculature 10 Musculature, gonads Outer skin, nervous system Germ line (future gametes) Musculature Hatching Intestine Intestine Anus Mouth Eggs Vulva POSTERIOR ANTERIOR 1.2 mm Determination of germ cell fate in C. elegans. 100 m How does distribution of the gray crescent affect the developmental potential of the first two daughter cells? EXPERIMENT Control egg (dorsal view) Experimental egg (side view) 1a Control 1b Experimental group group Gray crescent Gray crescent Thread 2 RESULTS Normal Belly piece Normal Figure 47.7b 0.25 mm Animal pole 8-cell stage (viewed from the animal pole) Figure 47.7c 0.25 mm Blastocoel Blastula (at least 128 cells) Can the dorsal lip of the blastopore induce cells in another part of the amphibian embryo to change their developmental fate? EXPERIMENT Dorsal lip of blastopore Pigmented gastrula (donor embryo) RESULTS Primary embryo Secondary (induced) embryo Nonpigmented gastrula (recipient embryo) Primary structures: Neural tube Notochord Secondary structures: Notochord (pigmented cells) Neural tube (mostly nonpigmented cells) Figure 47.24 Anterior Limb bud AER ZPA Posterior Limb buds 50 m 2 Digits Apical ectodermal ridge (AER) Anterior 3 4 Ventral Proximal Distal Dorsal Posterior (a) Organizer regions (b) Wing of chick embryo • One limb bud–regulating region is the apical ectodermal ridge (AER) • The AER is thickened ectoderm at the bud’s tip • The second region is the zone of polarizing activity (ZPA) • The ZPA is mesodermal tissue under the ectoderm where the posterior side of the bud is attached to the body © 2011 Pearson Education, Inc. EXPERIMENT Anterior New ZPA Donor limb bud Host limb bud ZPA Posterior RESULTS What happens when you put ZPA on both sides of a budding limb? Could you make a human with pinkies on both sides of their hands? EXPERIMENT Anterior New ZPA What role does the zone of polarizing activity (ZPA) play in limb pattern formation in vertebrates? Donor limb bud Host limb bud ZPA Posterior RESULTS 4 3 2 2 4 3 • Sonic hedgehog is an inductive signal for limb development • Hox genes also play roles during limb pattern formation © 2011 Pearson Education, Inc. Homeotic genes • Mutations to homeotic genes produce flies with such strange traits as legs growing from the head in place of antennae. antennapedia – structures characteristic of a particular part of the flies animal arise in wrong place Homeobox DNA • Master control genes evolved early • Conserved for hundreds of millions of years • Homologous homeobox genes in fruit flies & vertebrates – kept their chromosomal arrangement Cilia and Cell Fate • Ciliary function is essential for proper specification of cell fate in the human embryo • Motile cilia play roles in left-right specification • Monocilia (nonmotile cilia) play roles in normal kidney development © 2011 Pearson Education, Inc. Figure 47.26 Lungs Heart Liver Spleen Stomach Large intestine Normal location of internal organs Location in situs inversus