Transcript a. Sperm
CHAPTER 54 LECTURE SLIDES To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Animal Development Chapter 54 Fertilization • In all sexually-reproducing animals, the first step is fertilization – union of male and female gametes • Fertilization itself consists of three events – Sperm penetration and membrane fusion – Egg activation – Fusion of nuclei 3 Fertilization • Sperm penetration and membrane fusion – Protective layers of egg include the jelly layer and vitelline envelope in sea urchins, and the zona pellucida in mammals – Sperm’s acrosome contains digestive enzymes that enable the sperm to tunnel its way through to the egg’s cell membrane – Membrane fusion permits sperm nucleus to enter directly into egg’s cytoplasm 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm a. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm a. Jelly layer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Jelly layer Plasma membrane a. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Jelly layer Plasma membrane Vitelline envelope a. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Jelly layer Plasma membrane Vitelline envelope Nucleus of egg a. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Jelly layer Plasma membrane Vitelline envelope Cytoplasm a. Nucleus of egg Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Jelly layer Plasma membrane Vitelline envelope Cytoplasm Cortical granules a. Nucleus of egg Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Oocyte Granulosa cell c. b. d. c-d: © David M. Phillips/Visuals Unlimited 1.2 µm 3.3 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Granulosa cell Oocyte Granulosa cell c. b. d. c-d: © David M. Phillips/Visuals Unlimited 1.2 µm 3.3 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Granulosa cell Zona pellucida Oocyte Granulosa cell c. b. d. c-d: © David M. Phillips/Visuals Unlimited 1.2 µm 3.3 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Granulosa cell Zona pellucida Oocyte Plasma membrane Granulosa cell c. b. d. c-d: © David M. Phillips/Visuals Unlimited 1.2 µm 3.3 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Granulosa cell Zona pellucida Oocyte Plasma membrane Granulosa cell First polar body b. c. d. c-d: © David M. Phillips/Visuals Unlimited 1.2 µm 3.3 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Granulosa cell Zona pellucida Oocyte Plasma membrane Granulosa cell First polar body c. 1.2 µm Cytoplasm b. d. c-d: © David M. Phillips/Visuals Unlimited 3.3 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Granulosa cell Sperm Zona pellucida Oocyte Plasma membrane Granulosa cell First polar body Cortical granules c. 1.2 µm Cytoplasm b. d. c-d: © David M. Phillips/Visuals Unlimited 3.3 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sperm Granulosa cell Sperm Jelly layer Zona pellucida Plasma membrane Oocyte Plasma membrane Vitelline envelope Granulosa cell First polar body Cytoplasm 1.2 µm Nucleus of egg Cortical granules a. c. Cortical granules Cytoplasm b. d. c-d: © David M. Phillips/Visuals Unlimited 3.3 µm Fertilization 1. Sperm penetrates 2. Some of the zona 4. The sperm nucleus 3. Sperm and egg between granulosa pellucida is degraded dissociates and plasma membranes cells. by acrosomal enzymes. enters cytoplasm. fuse. Plasma membrane Granulosa cells Zona pellucida Cortical granules 6. Additional sperm can no longer penetrate the zona pellucida. 5. Cortical granules release enzymes that harden zona pellucida and strip it of sperm receptors. Hyalin attracts water by osmosis. 7. Sperm and egg pronuclei are enclosed in a nuclear envelope. 20 Fertilization • Membrane fusion – Egg activation • Dramatic increase in the levels of free intracellular Ca2+ ions in the egg shortly after the sperm makes contact with the egg’s plasma membrane • Act as second messengers to initiate changes – Block to polyspermy • Rapid transient change in membrane potential • Cortical granules remove sperm receptors • Vitelline envelope lifts off – fertilization envelope 21 Fertilization • Sperm penetration has three other effects – Triggers the egg to complete meiosis – Triggers a cytoplasmic rearrangement – Causes a sharp increase in protein synthesis and metabolic activity in general Primary Oocyte First Metaphase of Meiosis Second Metaphase of Meiosis Diploid nucleus Meiosis Complete Polar bodies Polar body Female pronucleus (haploid) • Roundworms (Ascaris) • Polychaete worms (Myzostoma) • Clam worms (Nereis) • Clams (Spisula) • Nemertean worms (Cerebratulus) • Polychaete worms (Chaetopterus) • Mollusks (Dentalium) • Many insects • Sea stars • Lancelets (Branchiostoma) • Amphibians • Mammals • Fish • Cnidarians • Sea urchins 22 Fertilization • Fusion of nuclei – 3rd and final stage of fertilization – Haploid sperm and haploid egg nuclei fuse to form diploid nucleus of the zygote 23 Cleavage • Rapid division of the zygote into a larger and larger number of smaller and smaller cells (blastomeres) • Not accompanied by an increase in the overall size of the embryo • Animal pole – Forms external tissues • Vegetal pole – Forms internal tissues 24 Cleavage • Blastula – Hollow ball of cells – Blastocoel – fluid-filled cavity • Cleavage patterns are quite diverse – Relative amount of nutritive yolk in the egg is the characteristic that most affects the cleavage pattern of an animal embryo – Vertebrates exhibit a variety of reproductive strategies involving different patterns of yolk utilization 25 Cleavage Patterns • Eggs with little or no yolk – Holoblastic cleavage – Invertebrates, amphibians, mammals • Eggs with large amounts of yolk – Meroblastic cleavage – Embryo forms thin cap on yolk Sea Urchin Frog Chicken Animal pole Nucleus Cytoplasm Cytoplasm Shell Nucleus Air bubble Nucleus Plasma membrane Albumen Yolk Yolk Vegetal pole a. b. Yolk 26 c. Holoblastic cleavage Meroblastic cleavage 27 28 Cleavage Patterns • Mammalian eggs contain very little yolk – Undergo holoblastic cleavage – Form a blastocyst composed of • Trophoblast – Outer layer of cells – Contributes to the placenta • Blastocoel – Central fluid-filled cavity • Inner cell mass – Located at one pole – Forms the developing embryo 29 Cleavage Patterns ICM Blastocoel Blastodisc Yolk Trophoblast 30 Fate of Blastomeres • In many animals removal of committed cells results in embryos deficient in tissues that would have developed from those tissues • In mammals, early blastomeres do not appear to be committed to a particular fate – Cell removed for preimplantation genetic diagnosis – Split embryos form identical twins • In mammals, body form determined primarily by cell-to-cell interactions 31 Gastrulation • Process involving a complex series of cell shape changes and cell movements that occurs in the blastula • Establishes the basic body plan and creates the three primary germ layers – Ectoderm – Exterior • Epidermis of skin, nervous system, sense organs – Mesoderm – Middle • Skeleton, muscles, blood vessels, heart, blood, gonads, kidneys, dermis of skin – Endoderm – Inner • Lining of digestive and respiratory tracts, liver, pancreas, thymus, thyroid 32 Gastrulation • Cells move during gastrulation using a variety of cell shape changes – Cells that are tightly attached to each other via junctions will move as cell sheets – Invagination – Cell sheet dents inward – Involution – Cell sheet rolls inward – Delamination – Cell sheet splits in two – Ingression – Cells break away from cell sheet and migrate as individual cells 33 Gastrulation Patterns • Vary according to the amount of yolk • Gastrulation in sea urchins – Develop from relatively yolk-poor eggs – Form hollow symmetrical blastulas – Deuterostome – anus develops first and mouth second 34 Animal pole Ectoderm Future ectoderm Ectoderm Blastocoel Primary mesenchyme cells (PMC’s) Vegetal pole a. Filopodia Archenteron PMC Future endoderm Blastopore b. Anus c. 35 Gastrulation Patterns • Gastrulation in frogs – Asymmetrical yolk distribution – Yolk-laden cells of the vegetal pole are less numerous but much larger than the yolk-free cells of the animal pole • Makes gastrulation more complex 36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Animal pole Dorsal lip Ectoderm Ectoderm Mesoderm Archenteron Endoderm Ectoderm Archenteron Blastocoel Blastocoel Mesoderm Vegetal pole a. Blastocoel Yolk plug Dorsal lip of blastopore Ventral lip b. c. Neural plate Neural fold Neural plate 37 d. e. Gastrulation Patterns • Gastrulation in birds – At the end of cleavage in a bird or reptile, the developing embryo is a small cap of cells called the blastoderm • Sits on top of the large ball of yolk – Upper layer of the blastoderm gives rise to all three germ layers 38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blastoderm Yolk Blastocoel Yolk Primitive streak Mesoderm Ectoderm Endoderm Yolk 39 Gastrulation Patterns • Gastrulation in mammals – Proceeds similarly to that in birds – Embryo develops from inner cell mass – Embryo gastrulates as if it was sitting in a ball of yolk • Embryo obtains nutrition from placenta 40 Gastrulation Patterns Inner cell mass Primitive streak Amniotic cavity Ectoderm Ectoderm Mesoderm Formation of yolk sac Trophoblast a. b. Endoderm c. Endoderm d. 41 Extraembryonic Membranes • Adaptation to life on dry land – Reptiles, birds, and mammals – Amniotic species developed • Extraembryonic membranes – Amnion, chorion, yolk sac, and allantois • Nourish and protect the developing embryo 42 Extraembryonic Membranes • Amnion – Encloses amniotic fluid • Chorion – Located near eggshell in birds – Contributes to the placenta in mammals • Yolk sac – Food source in bird embryos – Found in mammals, but it is not nutritive • Allantois – Unites with chorion in birds, forming a structure used for gas exchange – In mammals, it contributes blood vessels to the developing umbilical cord 43 Extraembryonic Membranes Chick Embryo Mammal Embryo Chorion Amnion Chorion Yolk sac Amnion Umbilical blood vessels Yolk sac Villus of chorion frondosum Allantois Maternal blood a. b. 44 Organogenesis • Formation of organs in their proper locations • Occurs by interaction of cells within and between the three germ layers • Thus, it follows rapidly on the heels of gastrulation – In many animals it begins before gastrulation is complete 45 Organogenesis • To a large degree, a cell’s location in the developing embryo determines its fate • At some stage, every cell’s ultimate fate becomes fixed – cell determination • A cell’s fate can be established by – Inheritance of cytoplasmic determinants – Interactions with neighboring cells • Induction 46 Organogenesis in Drosophila • Salivary gland development – Sex combs reduced (scr) gene is a homeotic gene in the Antennapedia complex • Prior to organogenesis, it is expressed in an anterior band of cells – At the same time, Decapentaplegic protein (Dpp) is released from dorsal cells • Forms a gradient in the dorsal–ventral direction • Determines ventral position of salivary glands – During organogenesis, salivary glands develop in areas where Scr is expressed and Dpp is absent 47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prior to Organogenesis Dpp a. During Organogenesis Salivary gland Labium b. 48 Organogenesis in Vertebrates • Begins with the formation of two structures unique to chordates – Notochord – Dorsal nerve cord – neurulation 49 Development of Neural Tube • Notochord – Forms from mesoderm – Region of dorsal ectodermal cells situated above notochord thickens to form the neural plate – Cells of the neural plate fold together to form a long hollow cylinder, the neural tube – Will become brain and spinal cord 50 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neural plate Amniotic cavity Ectoderm Mesoderm Notochord Endoderm Yolk sac a. Neural groove Neural fold Ectoderm Notochord Mesoderm Endoderm b. Neural tube Ectoderm Neural crest Mesoderm Endoderm Somite 51 c. Generation of Somites • While the neural tube is forming from dorsal ectoderm, the rest of the basic architecture of the body is being rapidly established by changes in the mesoderm • Sheets of mesoderm on either side of the developing notochord separate into a series of rounded regions called somitomeres • Somitomeres then separate into segmented blocks called somites • Cells at the presumptive boundary regions in the presomitic mesoderm instruct cells anterior to them to condense and separate into somites at certain times – Contact-mediated signaling 52 Generation of Somites • Mesoderm in the head region remains connected as somitomeres – Form muscles of the face, jaws, and throat • Some body organs develop within a strip of mesoderm lateral to each row of somites – Kidneys, adrenal glands, and gonads • Remainder of mesoderm moves out to surround the endoderm completely • Mesoderm separates into two layers – Coelom forms in between 53 Copyright © The McGraw-Hill Companies, Inc. 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Chordamesoderm Notochord Intermediate mesoderm Kidney Gonads Circulatory system Lateral plate mesoderm Linings of body cavities Extraembryonic Head Paraxial mesoderm Somite Cartilage Skeletal muscle Dermis 54 Neural Crest Cells • Neurulation occurs in all chordates – In vertebrates it is accompanied by an additional step • Just before the neural groove closes to form the neural tube, its edges pinch off, forming a small cluster of cells called the neural crest • These cells migrate to colonize many different regions of developing embryo 55 Neural Crest Cells • Neural crest cells migrate along pathways – Cranial neural crest cells are anterior cells that migrate into the head and neck • Contribute to skeletal and connective tissues of the face and skull, as well as differentiating into nerve and glial cells of the nervous system, and melanocyte pigment cells – Trunk neural crest cells are posterior cells that migrate in two pathways • Ventral pathway cells differentiate into sensory neurons and Schwann cells • Lateral pathway cells differentiate into melanocytes of the skin 56 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Epidermis Neural tube Posterior Lateral Pathway Cells take a dorsolateral route between the epidermis and somites Neural crest cells Anterior Aorta Notochord a. Posterior somite Anterior somite Ventral Pathway Cells travel ventrally through the anterior half of each somite Ventral Pathway Cell Fates Lateral Pathway Cell Fates Dorsal root ganglia Ventral root Schwann cells Melanocytes Sympathetic ganglia Adrenal medulla b. 57 Neural Crest Cells • Many of the unique vertebrate adaptations that contribute to their varied ecological roles involve neural crest derivatives • For example, gill chambers provided a greatly improved means of gas exchange • Allowed transition from filter feeding to active predation (higher metabolic rate) • Other changes – Better prey detection, and rapid response to sensory information 58 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chordates Vertebrates Zygote Pharynx Lining of respiratory tract Lining of digestive tract Endoderm Blastula Gastrula Ectoderm Neural crest Gill arches, sensory ganglia, Schwann cells, adrenal medulla Liver Mesoderm Outer covering of internal organs Lining of thoracic and abdominal cavities Dorsal nerve cord Epidermis, skin, hair, epithelium, inner ear, lens of eye Major glands Pancreas Brain, spinal cord, spinal nerves Notochord Circulatory system Integuments Blood Heart Vessels Somites Gonads Kidney Dermis Skeleton Striated muscles 59 Vertebrate Axis Formation • Hans Spemann and Hilde Mangold transplanted cells of the dorsal lip of one embryo into the future belly region of another • Some of the embryos developed two notochords: a normal dorsal one, and a second one along the belly • Moreover, a complete set of dorsal axial structures formed at the ventral transplantation site in most embryos • Transplanted donor cells acted as organizers 60 Vertebrate Axis Formation Donor embryo Recipient embryo Primary neural fold Primary notochord, somites, and neural development Dorsal lip Secondary neural fold Secondary notochord, somites, and neural development Primary embryo Secondary embryo 61 Organizers • An organizer is a cluster of cells that release diffusible signal molecules which convey positional information to other cells – The closer a cell is to an organizer, the higher the concentration of the signal molecule (morphogen) it experiences – Organizers and the diffusible morphogens that they release are thought to be part of a widespread mechanism for determining relative position and cell fates during vertebrate development 62 Induction • Primary induction occurs between the three primary germ layers – Differentiation of the central nervous system during neurulation • Secondary induction occurs between tissues that have already been specified to develop along a particular pathway – Development of the lens of the vertebrate eye 63 Wall of forebrain Ectoderm Optic cup Lens vesicle Neural cavity Optic stalk Lens invagination Lens Optic nerve Lens Sensory layer Pigment layer • An extension of the optic stalk grows until it contacts the surface ectoderm, where it induces a section of the ectoderm to pinch off and form the lens • Other structures of the eye develop from the optic stalk, with lens cells reciprocally inducing the formation of photoreceptors in the optic cup 64 Retina Human Development • Human development from fertilization to birth takes an average of 266 days, or about 9 months – Commonly divided into three periods called trimesters 65 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First Trimester • First month a. © Lennart Nilsson/Albert Bonniers Förlag AB, A Child Is Born, Dell Publishing Company – Zygote undergoes its first cleavage about 30 hr after fertilization – By the time the embryo reaches the uterus, 6–7 days after fertilization, it has differentiated into a blastocyst – Trophoblast cells digest their way into the endometrium in the process known as implantation 66 First Trimester • First month – During the second week, the developing chorion and mother’s endometrium engage to form the placenta • Mom and baby’s blood come into close proximity, but do not mix – gases are exchanged • One hormone released by the placenta is human chorionic gonadotropin (hCG) – – – – Gastrulation occurs in the second week Neurulation occurs in the third week Organogenesis begins in the fourth week Embryo is 5 mm in length 67 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chorion Amnion Yolk sac Umbilical cord Chorionic frondosum (fetal) Decidua basalis (maternal) Placenta Umbilical artery Umbilical vein Uterine wall a. 68 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First Trimester • Second month – Organogenesis continues – Miniature limbs assume adult shape – All major organs in the body established – Embryo grows to about 25 mm in length – Weighs about 1 g, and looks distinctly human – 9th week marks the transition from embryo to fetus b. © Lennart Nilsson/Albert Bonniers Förlag AB, A Child Is Born, Dell Publishing Company 69 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First Trimester • Third month – Nervous system develops c. – Limbs start to move – Secretion of hCG by the placenta declines, and so corpus luteum degenerates – Placenta takes over hormone secretion © Lennart Nilsson/Albert Bonniers Förlag AB, A Child Is Born, Dell Publishing Company 70 Increasing Hormone Concentration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. hCG Estrogen Progesterone 0 1 2 3 4 5 6 Months of Pregnancy 7 8 9 71 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Second Trimester d. © Lennart Nilsson/Albert Bonniers Förlag AB, A Child Is Born, Dell Publishing Company • The basic body plan develops further • Bones actively enlarge in fourth month • Rapid fetal heartbeat can be heard by a stethoscope • By the end of the sixth month, fetus is over 300 mm long, and weighs 600 g 72 Third Trimester • A period of growth and organ maturation • Weight of the fetus doubles several times • Most of the major nerve tracts in the brain are formed • Brain continues to develop and produce neurons for months after birth 73 Birth • Estrogen stimulates mother’s uterus to release prostaglandins, and produce more oxytocin receptors – Prostaglandins begin uterine contractions – Sensory feedback from uterus stimulates oxytocin release from posterior pituitary • Oxytocin and prostaglandins further stimulate uterine contractions 74 Birth • Strong contractions, aided by the mother’s voluntary pushing, expel the fetus • Now called a newborn baby, or neonate • After birth, continuing uterine contractions expel the placenta and associated membranes – Collectively called the afterbirth 75 Copyright © The McGraw-Hill Companies, Inc. 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Intestine Placenta Umbilical cord Wall of uterus Cervix Vagina 76 Nursing • Milk production (lactation) occurs in alveoli of mammary glands when stimulated by the anterior pituitary hormone prolactin • During pregnancy, the mammary glands are prepared for, but prevented from, lactating 77 Nursing • After birth – Prolactin – stimulates the mammary alveoli to produce milk – Suckling triggers posterior pituitary to release oxytocin • Stimulates contraction of smooth muscles surrounding alveolar ducts • Milk is ejected (milk let-down reflex) • The first milk produced after birth, colostrum, is rich in nutrients and maternal antibodies 78 Postnatal Development • Growth of the infant continues rapidly after birth • Babies typically double their birth weight within 2 months • Different components grow at different rates – Allometric growth 79 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). 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