1. 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 © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Animal Development Chapter 47

2. Figure 47.2 EMBRYONIC DEVELOPMENT Sperm Adult frog Egg Metamorphosis Larval stages Zygote Blastula Gastrula Tail-bud embryo FERTILIZATION CLEAVAGE GASTRULATION ORGANO- GENESIS

3. Concept 47.1: Fertilization and cleavage initiate embryonic development Fertilization is the formation of a diploid zygote from a haploid egg and sperm © 2011 Pearson Education, Inc.

4. Fertilization Molecules and events at the egg surface play a crucial role in each step of fertilization –Sperm penetrate the protective layer around the egg –Receptors on the egg surface bind to molecules on the sperm surface –Changes at the egg surface prevent polyspermy, the entry of multiple sperm nuclei into the egg © 2011 Pearson Education, Inc.

5. The Acrosomal Reaction The acrosomal reaction is triggered when the sperm meets the egg The acrosome at the tip of the sperm releases hydrolytic enzymes that digest material surrounding the egg © 2011 Pearson Education, Inc.

6. Figure 47.3-5 Basal body (centriole) Sperm plasma membrane Sperm nucleus Sperm head Acrosome Jelly coat Sperm-binding receptors Fertilization envelope Cortical granule Fused plasma membranes Hydrolytic enzymes Vitelline layer Egg plasma membrane Perivitelline space EGG CYTOPLASM Actin filament Acrosomal process

7. Gamete contact and/or fusion depolarizes the egg cell membrane and sets up a fast block to polyspermy © 2011 Pearson Education, Inc.

8. The Cortical Reaction Fusion of egg and sperm also initiates the cortical reaction Seconds after the sperm binds to the egg, vesicles just beneath the egg plasma membrane release their contents and form a fertilization envelope The fertilization envelope acts as the slow block to polyspermy © 2011 Pearson Education, Inc.

9. Egg Activation The rise in Ca 2+ 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.

10. In mammals the first cell division occurs 12  36 hours after sperm binding The diploid nucleus forms after this first division of the zygote © 2011 Pearson Education, Inc.

11. 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 © 2011 Pearson Education, Inc.

12. Figure 47.6 (a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula 50  m

13. In frogs and many other animals, the distribution of yolk (stored nutrients) is a key factor influencing the pattern of cleavage The vegetal pole has more yolk; the animal pole has less yolk The difference in yolk distribution results in animal and vegetal hemispheres that differ in appearance © 2011 Pearson Education, Inc. Cleavage Patterns

14. Zygote 2-cell stage forming 4-cell stage forming 8-cell stage Vegetal pole Blastula (cross section) Gray crescent Animal pole Blastocoel 0.25 mm 8-cell stage (viewed from the animal pole) Blastula (at least 128 cells) Figure 47.7

15. After cleavage, the rate of cell division slows and the normal cell cycle is restored 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. Concept 47.2: Morphogenesis in animals involves specific changes in cell shape, position, and survival

16. Gastrulation Gastrulation rearranges the cells of a blastula into a three-layered embryo, called a gastrula © 2011 Pearson Education, Inc.

17. The three layers produced by gastrulation are called embryonic germ layers –The ectoderm forms the outer layer –The endoderm lines the digestive tract –The mesoderm partly fills the space between the endoderm and ectoderm Each germ layer contributes to specific structures in the adult animal © 2011 Pearson Education, Inc.

18. ECTODERM (outer layer of embryo) MESODERM (middle layer of embryo) ENDODERM (inner layer of embryo) Epidermis of skin and its derivatives (including sweat glands, hair follicles) Epithelial lining of digestive tract and associated organs (liver, pancreas) Epithelial lining of respiratory, excretory, and reproductive tracts and ducts Germ cells Jaws and teeth Pituitary gland, adrenal medulla Nervous and sensory systems Skeletal and muscular systems Circulatory and lymphatic systems Excretory and reproductive systems (except germ cells) Dermis of skin Adrenal cortex Thymus, thyroid, and parathyroid glands Figure 47.8

19. Gastrulation begins at the vegetal pole of the blastula Mesenchyme cells migrate into the blastocoel The vegetal plate forms from the remaining cells of the vegetal pole and buckles inward through invagination © 2011 Pearson Education, Inc. Gastrulation in Sea Urchins

20. The newly formed cavity is called the archenteron This opens through the blastopore, which will become the anus © 2011 Pearson Education, Inc.

21. Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Blastocoel Filopodia Mesenchyme cells Blastopore Archenteron 50  m Ectoderm Mouth Mesenchyme (mesoderm forms future skeleton) Blastopore Blastocoel Archenteron Digestive tube (endoderm) Anus (from blastopore) Key Future ectoderm Future mesoderm Future endoderm Figure 47.9

22. Cells continue to move from the embryo surface into the embryo by involution These cells become the endoderm and mesoderm Cells on the embryo surface will form the ectoderm © 2011 Pearson Education, Inc.

23. Key Future ectoderm Future mesoderm Future endoderm SURFACE VIEW CROSS SECTION Animal pole Vegetal pole Early gastrula Blastocoel Dorsal lip of blasto- pore Blastopore Dorsal lip of blastopore Blastocoel shrinking Archenteron Blastocoel remnant Ectoderm Mesoderm Endoderm Blastopore Yolk plug Blastopore Late gastrula 321 Figure 47.10

24. Developmental Adaptations of Amniotes The colonization of land by vertebrates was made possible only after the evolution of –The shelled egg of birds and other reptiles as well as monotremes (egg-laying mammals) –The uterus of marsupial and eutherian mammals © 2011 Pearson Education, Inc.

25. In both adaptations, embryos are surrounded by fluid in a sac called the amnion This protects the embryo from desiccation and allows reproduction on dry land Mammals and reptiles including birds are called amniotes for this reason © 2011 Pearson Education, Inc.

26. The four extraembryonic membranes that form around the embryo –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.

27. Organogenesis During organogenesis, various regions of the germ layers develop into rudimentary organs Early in vertebrate organogenesis, the notochord forms from mesoderm, and the neural plate forms from ectoderm © 2011 Pearson Education, Inc.

28. Figure 47.13 Neural folds 1 mm Neural fold Neural plate Notochord Ectoderm Mesoderm Endoderm Archenteron (a) Neural plate formation (b) Neural tube formation (c) Somites Neural fold Neural plate Neural crest cells Outer layer of ectoderm Neural crest cells Neural tube Eye SomitesTail bud SEM Neural tube Notochord Coelom Neural crest cells Somite Archenteron (digestive cavity) 1 mm

29. The neural plate soon curves inward, forming the neural tube The neural tube will become the central nervous system (brain and spinal cord) © 2011 Pearson Education, Inc.

30. Programmed cell death is also called apoptosis At various times during development, individual cells, sets of cells, or whole tissues stop developing and are engulfed by neighboring cells For example, many more neurons are produced in developing embryos than will be needed Extra neurons are removed by apoptosis © 2011 Pearson Education, Inc. Programmed Cell Death

31. Concept 47.3: Cytoplasmic determinants and inductive signals contribute to cell fate specification 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 © 2011 Pearson Education, Inc.

32. Cells in a multicellular organism share the same genome Differences in cell types are the result of the expression of different sets of genes © 2011 Pearson Education, Inc.

33. Fate Mapping Fate maps are diagrams showing organs and other structures that arise from each region of an embryo Classic studies using frogs indicated that cell lineage in germ layers is traceable to blastula cells © 2011 Pearson Education, Inc.

34. Epidermis Central nervous system Notochord Mesoderm Endoderm BlastulaNeural 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 Figure 47.17

35. Later studies of C. elegans used the ablation (destruction) of single cells to determine the structures that normally arise from each cell The researchers were able to determine the lineage of each of the 959 somatic cells in the worm © 2011 Pearson Education, Inc.

36. First cell division Zygote Hatching Time after fertilization (hours) Intestine Mouth EggsVulva Anus 1.2 mm ANTERIOR POSTERIOR Nervous system, outer skin, muscula- ture Muscula- ture, gonads Outer skin, nervous system Germ line (future gametes) Musculature 10 0 Figure 47.18

37. Restricting Developmental Potential Hans Spemann performed experiments to determine a cell’s developmental potential (range of structures to which it can give rise) Embryonic fates are affected by distribution of determinants and the pattern of cleavage The first two blastomeres of the frog embryo are totipotent (can develop into all the possible cell types) © 2011 Pearson Education, Inc.

38. Control egg (dorsal view) 1a1b Gray crescent Control group Experimental group Experimental egg (side view) Gray crescent EXPERIMENT Thread Figure 47.22-1

39. Control egg (dorsal view) 2 1a1b Gray crescent Control group Experimental group Experimental egg (side view) Gray crescent Thread Normal Belly piece EXPERIMENT RESULTS Figure 47.22-2

40. In mammals, embryonic cells remain totipotent until the 8-cell stage, much longer than other organisms Progressive restriction of developmental potential is a general feature of development in all animals In general tissue-specific fates of cells are fixed by the late gastrula stage © 2011 Pearson Education, Inc.