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1 mm Morphogenesis process by which an animal takes shape determined by genome and differences between embryonic cells.

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Presentation on theme: "1 mm Morphogenesis process by which an animal takes shape determined by genome and differences between embryonic cells."— Presentation transcript:

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2 1 mm

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4 Morphogenesis process by which an animal takes shape determined by genome and differences between embryonic cells

5 The Acrosomal Reaction Triggered when sperm reaches egg releases hydrolytic enzymes that digest material surrounding the egg

6 Sperm-binding receptors Jelly coat Acrosome Actin Sperm head Basal body (centriole) Sperm plasma membrane Sperm nucleus Contact Acrosomal reaction Acrosomal process Contact and fusion of sperm and egg membranes Entry of sperm nucleus Cortical reaction Fertilization envelope Egg plasma membrane Vitelline layer Hydrolytic enzymes Cortical granule Fused plasma membranes Perivitelline space Cortical granule membrane EGG CYTOPLASM

7 The Cortical Reaction Initiated by the fusion of egg and sperm induces a rise in Ca 2+ stimulates cortical granules to release their contents outside the egg cause formation of a fertilization envelope block to polyspermy

8 1 sec before fertilization Point of sperm entry 10 sec after fertilization Spreading wave of calcium ions 20 sec 30 sec 500 µm

9 Activation of the Egg sharp rise in Ca 2+ increases the rates of cellular respiration and protein synthesis by the egg cell = activation of egg cell

10 Binding of sperm to egg Acrosomal reaction: plasma membrane depolarization (fast block to polyspermy) Increased intracellular calcium level Cortical reaction begins (slow block to polyspermy) Formation of fertilization envelope complete Increased intracellular pH Fusion of egg and sperm nuclei complete Increased protein synthesis Onset of DNA synthesis First cell division 1 Seconds Minutes

11 Fertilization in Mammals the cortical reaction modifies the zona pellucida as a slow block to polyspermy

12 Follicle cell Acrosomal vesicle Egg plasma membrane Zona pellucida Sperm nucleus Cortical ganules Sperm basal body EGG CYTOPLASM

13 Cleavage a period of rapid cell division without growth partitions the cytoplasm of one large cell into many smaller cells blastomeres

14 Fertilized egg Four-cell stage Morula Blastula

15 Polarity eggs and zygotes of many animals (except mammals) Animal pole Vegetal pole Most of yolk

16 Anterior Right Animal pole Gray crescent Dorsal Ventral Left Posterior Body axes Establishing the axes Future dorsal side of tadpole Point of sperm entry First cleavage Vegetal hemisphere Vegetal pole Point of sperm entry Animal hemisphere

17 Cleavage planes follow a pattern relative to the zygotes animal and vegetal poles

18 Zygote 2-cell stage forming 8-cell stage 4-cell stage forming Animal pole Blasto- coel Blastula (cross section) Vegetal pole Blastula (at least 128 cells) 0.25 mm Eight-cell stage (viewed from the animal pole) 0.25 mm

19 Meroblastic cleavage incomplete division of the egg occurs in species with yolk-rich eggs Ie. reptiles and birds

20 Blastocoel Fertilized egg BLASTODERM Hypoblast Epiblast YOLK MASS Cutaway view of the blastoderm Blastoderm Four-cell stage Zygote Disk of cytoplasm

21 Holoblastic cleavage complete division of the egg occurs in species whose eggs have little or moderate amounts of yolk Ie. sea urchins and frogs

22 Gastrulation rearranges the cells of a blastula into a three-layered embryo a gastrula has a primitive gut

23 The three layers produced by gastrulation are called embryonic germ layers The ectoderm f orms the outer layer The endoderm l ines the digestive tract The mesoderm p artly fills the space between the endoderm and ectoderm Video: Sea Urchin Embryonic Development Video: Sea Urchin Embryonic Development

24 Animal pole Blastopore Filopodia pulling archenteron tip Archenteron Mesenchyme cells Blastocoel Future ectoderm Vegetal pole Key Future mesoderm Future endoderm Vegetal plate Blastocoel Mesenchyme cells Archenteron Blastocoel Mesenchume (mesoderm forms future skeleton) 50 µm Mouth Ectoderm Blastopore Digestive tube (endoderm) Anus (from blastopore)

25 Future ectoderm Key Future mesoderm Future endoderm Archenteron Blastocoel remnant Ectoderm Mesoderm Endoderm Yolk plug Gastrula Blastocoel shrinking Blastocoel Dorsal tip of blastopore CROSS SECTION Animal pole Dorsal lip of blastopore Vegetal pole Blastula SURFACE VIEW

26 Organogenesis regions of the germ layers develop into rudimentary organs the notochord forms from mesoderm the neural plate forms from ectoderm curves inward, forming the neural tube Video: Frog Embryo Development Video: Frog Embryo Development

27 Neural folds Neural plate LM 1 mm Neural fold Notochord Archenteron Neural plate formation Endoderm Mesoderm Ectoderm

28 Neural fold Neural plate Neural tube Formation of the neural tube Neural crest Outer layer of ectoderm Neural crest

29 Somites blocks Formed from mesoderm lateral to the notochord Coelom Lateral to the somites mesoderm splits to form the coelom

30 1 mm Notochord Archenteron (digestive cavity) Neural tube Neural crest Eye Somites Tail bud SEM Coelom Somite Somites

31 Notochord Archenteron Endoderm Mesoderm Ectoderm Neural tube Eye Coelom Somite Somites Neural tube Lateral fold Yolk stalk YOLK Form extraembryonic membranes Yolk sac Early organogenesis Forebrain Heart Blood vessels Late organogenesis

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33 Adaptations of Amniotes develop in a fluid-filled sac in a shell or the uterus Birds Reptiles mammals Germ layers give rise to membranes surrounding embryos

34 Embryo Amniotic cavity with amniotic fluid Allantois Amnion Albumen Yolk (nutrients) Yolk sac Chorion Shell

35 Mammalian Development eggs of placental mammals Small store few nutrients Exhibit holoblastic cleavage Show no obvious polarity Gastrulation and organogenesis similar to birds and reptiles Early cleavage is relatively slow

36 Cleavage forms the blastocyst forms trophoblast, the outer epithelium of the blastocyst, initiates implantation in the uterus, and the blastocyst forms a flat disk of cells As implantation is completed, gastrulation begins The extraembryonic membranes begin to form By the end of gastrulation, the embryonic germ layers have formed

37 Blastocyst reaches uterus. Endometrium (uterine lining) Maternal blood vessel Blastocyst implants. Inner cell mass Trophoblast Blastocoel Hypoblast Trophoblast Epiblast Expanding region of trophoblast

38 Hypoblast Chorion (from trophoblast Epiblast Amniotic cavity Amnion Yolk sac (from hypoblast) Extraembryonic mesoderm cells (from epiblast) Extraembryonic membranes start to form and gastrulation begins. Amnion Chorion Endoderm Mesoderm Ectoderm Yolk sac Extraembryonic mesoderm Gastrulation has produced a three-layered embryo with four extraembryonic membranes. Allantois Expanding region of trophoblast

39 Fate Maps general territorial diagrams of embryonic development

40 Fate map of a frog embryo Epidermis Central nervous system Blastula Epidermis Neural tube stage (transverse section) Endoderm Mesoderm Notochord

41 Development Differentiation Signal molecules Influence gene

42 Anterior Organizer regions Limb bud Posterior ZPA AER 50 µm Apical ectodermal ridge


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