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General Biology gy II Lecture 2-4 Before the class C p e 477 Chapter Animal Development p • When a life begins? • How a life of animal starts? • What are the progress of fertilization? • How an embryo is developed into an individual? • How each cell knows its own fate? ݅ ᑣ ٫ Դৣ [email protected] General Biology lectured by Han-Jia Lin 2 Outlines Overview: A Body-Building Plan • A human embryo at about 7 weeks after conception shows development of distinctive features • Part1 – Fertilization – Cleavage • Part2 Part 2 – Gastrulation – Organgenesis • Part3: – Cellfatedeterminationandpatternformation Biology lectured ©General 2011 Pearson Education, Inc. by Han-Jia Lin 3 General Biology lectured by Han-Jia Lin 4 Stagesofembryonicdevelopment p Sperm AnimalDevelopment EMBRYONICDEVELOPMENT • Although animals display different body plans, they share h many basic b i mechanisms h i off d development l and d use a common set of regulatory genes Zygote • Cleavage Adult Egg f frog ϩය • Blastula ៶ ය ៶खය • Gastrulation Metamorphosis চဉය • Organogenesis Ꮤ۔ԋය • Metamorphosis Larval stages ᡂᄊය General Biology lectured by Han-Jia Lin Blastula Gastrula Tailbud embryo 5 Modelanimals General Biology lectured by Han-Jia Lin 6 Fertilization • Fertilization is the formation of a diploid p zygote yg from a haploid egg and sperm • C.elegans,Drosophila C l hil • Seaurchin,zebrafish,frog,chickandmouse , , g, • 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 Nature430,411412 General Biology lectured by Han-Jia Lin http://www.imcb.astar.edu.sg/pressarchive/170309p.php 7 – Changes at the egg surface prevent polyspermy, the entry of multiple sperm nuclei into the egg General Biology lectured by Han-Jia Lin 8 Acrosome Reaction The Acrosomal Reaction )ഗᡏϸᔈ* Sperm plasma membrane • The acrosomal reaction is triggered when the sperm meets the egg Sperm nucleus • Th The acrosome att the th tip ti off the th sperm releases l hydrolytic enzymes that digest material surrounding di th the egg Basal body (centriole) p Sperm head • Gamete contact and/or fusion depolarizes p the egg gg cell membrane and sets up a fast block to p y p polyspermy y General Biology lectured by Han-Jia Lin 9 Fertilization envelope l Acrosomal process Actin filament Cortical Fused granule plasma membranes b Hydrolytic enzymes Perivitelline space Vitelline layer Acrosome Jelly coat Sperm-binding receptors EGG CYTOPLASM Egg plasma membrane General Biology lectured by Han-Jia Lin Figure 47.4 10 EXPERIMENT The Cortical Reaction )Ҝ፦ϸᔈ** • Initiated by the fusion of egg and sperm • Seconds after the sperm binds to the egg, vesicles jjust beneath the egg gg p plasma membrane release their contents and form a fertilization envelope p acts as the slow block • The fertilization envelope to polyspermy • The cortical reaction requires a high concentration of Ca2 ions in the egg • Ca2 spread across the egg correlates with the appearance of the fertilization envelope General Biology lectured by Han-Jia Lin 11 10 sec after fertilization 25 sec 35 sec 1 min 10 sec after f tili ti fertilization 20 sec 30 sec 500 Pm RESULTS 1 sec before f tili ti fertilization 500 Pm m CONCLUSION Point of sperm nucleus entry General Biology lectured by Han-Jia Lin Spreading wave of Ca2 Fertilization envelope 12 Fertilization in Mammals Egg gg 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 i said is id tto b be activated ti t d • Secretions in the mammalian female reproductive t t alter tract lt sperm motility tilit and d structure t t • This is called capacitation, p , and must occur before sperm are able to fertilize an egg • The p proteins and mRNAs needed for activation are already present in the egg • The sperm nucleus merges with the egg nucleus and cell division begins General Biology lectured by Han-Jia Lin 13 General Biology lectured by Han-Jia Lin 14 Figure 47.5 Capacitation • Only in mammalian sperm – Not N t ready d tto ffertilize tili b before f capacitation! – Take place in female reproduction tract • Biochemical event • Reported in 1951 by both Min Chueh Chang and Collin Russel Austin, independently. p y No fast block in mammlian! Zona pellucida Follicle cell Key and Lock! Dr. Min Chueh Chang ܴ റγ 2:19.2::2 Sperm Sperm nucleus basal body General Biology lectured by Han-Jia Lin 15 General Biology lectured by Han-Jia Lin Cortical granules 16 Cleavage DurationofCleavageStage • Fertilizationisfollowedbycleavage,aperiodofrapid celldivisionwithoutgrowth • Cleavage Cleavagepartitionsthecytoplasmofonelargecell partitions the cytoplasm of one large cell intomanysmallercellscalledblastomeres (खယಒझ) • Theblastula(៶ख)isaballofcellswithafluidfilled cavitycalledablastocoel (៶ख๚) • In mammals the first cell division occurs 1236 h hours after ft sperm bi binding di • The diploid nucleus forms after this first division of the zygote • Zebrafish (cleavage2hr,blastula5hr) • Chicken(~24hr) • Mouseandhuman Blastocoel (5~6days) 50 Pm 50Pm (a)Fertilizedegg (b)Fourcellstage General Biology lectured by Han-Jia Lin (c)Earlyblastula Blastula(atleast128cells) (d)Laterblastula 17 General Biology lectured by Han-Jia Lin 18 Cleavagepattern First2cleavage • PolarityofZygote • Cytokinesis (SÆMÆSÆMphase) – Yolkisthekeyfactorforcleavage • Cleavagefurrowռྎ • Th Thevegetalpolehasmoreyolk;theanimalpole t l l h lk th i l l haslessyolk • Thefirst2cleavageproduce4blastomeres h f l d bl ofequal f l size • Meroblastic:theyolk istoobigthatcleavage furrow cannot pass furrowcannotpass throughit(bird,frog, fish…) • Holoblastic:human Animal p pole ނ ཱུ V Vegetal t l pole l ނ ཱུ Graycrescent Zygote yg General Biology lectured by Han-Jia Lin 0 25 0.25mm 19 2cellstage forming General Biology lectured by Han-Jia Lin 4cellstage forming • Graycrescent:ԪД 20 The3rd cleavage Inmostinsects • Equatorial • Spermandeggnucleifusewithinyolk! • Maybeasymmetric:becauseofthehugeyolkin meroblastic embryo! embryo! • Multipleroundsofmitosisoccurwithout cytokinesis! – Nocellmembranesformaroundtheearlynuclei (blastomeresinanimalpolearesmaller) 0.25mm Animalpole – Nucleimigratetotheouteredgeoftheembryo aandtheplasmamembraneformÆ d t e p as a e b a e o 6000cells 6000 ce s surrondingamassofyolk(similartoblastula) Animal pole Graycrescent Vegetalpole 4cellstage 2cellstage forming forming General Biology lectured by Han-Jia Lin Zygote 8cellstage 8cellstage(viewed fromtheanimalpole) 21 General Biology lectured by Han-Jia Lin Regulationofcleavage End of Part 1 • Howanembryoknowstheendofcleavagestage? Ask yourself…. – theratioofmaterialinthenucleusrelativetothe cytoplasm is sufficiently large cytoplasmissufficientlylarge 22 • How eggs could prevent polyspermy? • Wh What’s t’ diff differentt between b t mammalian li fertilization and other animals? – Exp:halfofthecytoplasmremoveÆ onefewer cleavageoccur… l • When is the start point of cleavage? • Theendofcleavagemeans… g • What is animal pole and vegetal pole? – EnoughcellsÆ enoughcopiesofchromosomeÆ enough RNA to program the cell’ssmetabolism enoughRNAtoprogramthecell metabolism • What is the sequence of cleavage? • How to control cleavage? General Biology lectured by Han-Jia Lin 23 General Biology lectured by Han-Jia Lin 24 Morphogenesis Gastrulation • Thecellularandtissuebasedprocessesbywhich theanimalbodytakesshapes. • Gastrulation rearrangesthecellsofablastula g intoathreelayeredembryo,calledagastrula (চဉख) • Thethreelayersproducedbygastrulation Th h l d db l i are calledembryonicgermlayers (खቫ) – Gastrulation • Asetofcellsfromsurfaceofblastulamovesto i interiorlocation i l i – The Theectodermformstheouterlayer ectoderm forms the outer layer – Theendodermlinesthedigestivetract – Themesodermpartlyfillsthespacebetweenthe The mesoderm partly fills the space between the endodermandectoderm • Celllayersestablished(2or3layers) y ( y ) • Aprimitivedigestivetubeisformed • Animalswithbilateralsymmetryaretriplobasts, h i havingmesoderm d • Eachgermlayercontributestospecificstructures in the adult animal intheadultanimal – Organogenesis • Theformationoforgans The formation of organs General Biology lectured by Han-Jia Lin 25 ECTODERM(outerlayerofembryo) 26 GastrulationinSeaUrchins •Epidermisofskinanditsderivatives(includingsweatglands, hairfollicles) •Nervousandsensorysystems • Pituitary gland adrenal medulla •Pituitarygland,adrenalmedulla •Jawsandteeth •Germcells • Gastrulation beginsatthevegetalpoleofthe begins at the vegetal pole of the blastula • Mesenchyme cellsmigrateintotheblastocoel cells migrate into the blastocoel MESODERM(middlelayerofembryo) • Thevegetalplateformsfromtheremainingcells ofthevegetalpoleandbucklesinwardthrough invagination •Skeletalandmuscularsystems •Circulatoryandlymphaticsystems •Excretoryandreproductivesystems(exceptgermcells) •Dermisofskin • Adrenal cortex •Adrenalcortex • Thenewlyformedcavityiscalledthe archenteron (চဉ) archenteron(চဉ) ENDODERM(innerlayerofembryo) •Epithelialliningofdigestivetractandassociatedorgans (liver,pancreas) •Epithelialliningofrespiratory,excretory,andreproductivetracts andducts dd •Thymus,thyroid,andparathyroidglands General Biology lectured by Han-Jia Lin General Biology lectured by Han-Jia Lin • Thisopensthroughtheblastopore (खα orচα), which will become the anus whichwillbecometheanus 27 General Biology lectured by Han-Jia Lin 28 Gastrulationbegins withthemigrationof mesenchymecells h ll (໔ယಒझ) Animal pole Blastocoel Mesenchyme cells Vegetalplate Threeaxisofbilaterallyanimals Vegetal pole Protostomes(চα)ނ Protostomes (চα)ނ BlastoporeÆ mouth Blastocoel Deuterostomes(ࡕα)ނ Deuterostomes (ࡕα)ނ BlastoporeÆ anus Aftergastrulation,the After gastrulation the larvaesofSeaurchinare zooplankton Filopodia Mesenchyme cells Archenteron Bl t Blastopore Aftermetamorphogenesis, theadultseaurchinsinkto theseafloor. 50Pm Blastocoel Ectoderm Key A h t Archenteron Blastopore Mouth Futureectoderm Future ectoderm Futuremesoderm Futureendoderm Mesenchyme (mesodermforms futureskeleton) Digestivetube(endoderm) b ( d d ) Anus(fromblastopore) General Biology lectured by Han-Jia Lin 29 GastrulationinFrogs • Cellscontinuetomovefromtheembryosurface ll i f h b f intotheembryobyinvolution(खजϣᙯ) • This Thisformsacreasealongtheregionwherethegray forms a crease along the region where the gray crescent(ԪД) formed – Thesecellsbecometheendodermandmesoderm – Cellsontheembryosurfacewillformtheectoderm C ll th b f ill f th t d • Th Thepartabovethecreaseiscalledthedorsallip t b th i ll d th d l li (ङয)oftheblastopore 1 Key Future ectoderm Future mesoderm Early Vegetalpole Future gastrula endoderm General Biology lectured by Han-Jia Lin 30 EmbryoInvolution • Frog Froggastrulationbeginswhenagroupofcellsonthe gastrulation begins when a group of cells on the dorsalsideoftheblastulabeginstoinvaginate SURFACEVIEW SURFACE VIEW Animalpole General Biology lectured by Han-Jia Lin 2 CROSS SECTION CROSSSECTION Key Blastocoel Dorsal Dorsal lipof blasto pore Blastopore Blastocoel shrinking Archenteron Future ectoderm d Future mesoderm Future Future endoderm Dorsal lipof blastopore 31 General Biology lectured by Han-Jia Lin 32 LateGastrulationinFrog Gastrulationinchicks • Priortogastrulation,theembryoiscomposedof anupperandlowerlayer,theepiblast(खቫ) andhypoblast(Πखቫ),respectively • Theblastocoeliscompletelyreplacedbythe endodermlined endoderm linedarchenteron archenteron 3 Future ectoderm Future mesoderm Future Future endoderm Ectoderm Mesoderm Endoderm Blastocoel remnant Key Late gastrula Blastopore • During Duringgastrulation,epiblastcellsmovetoward gastrulation epiblast cells move toward themidlineoftheblastodermandthenintothe embryotowardtheyolk b t d th lk • Themidlinethickensandiscalledtheprimitive p streak(চచ) Blastopore Yolk plug Yolkplug A h t Archenteron General Biology lectured by Han-Jia Lin 33 • Allthecellsthatwillformthe embryocomefromtheepiblast • Thehypoblastcellsdonot h h bl ll d contributetotheembryo • itcontributestothesac it contributes to the sac that that surroundstheyolkandaconnection betweentheyolkandtheembryo y y Fertilizedegg Primitive streak Embryo Yolk Gastrulationinhuman • human blastocyst (notblastulabecauseoflittle yolk)Æ Æ day6,>100cells Thetrophoblast trophoblast (Ꭶቫ)istheouterepithelial (Ꭶቫ) is the outer epithelial – The layeroftheblastocyst anddoesnotcontribute to the embryo but instead initiates implantation totheembryo,butinsteadinitiatesimplantation Epiblast Future Future ectoderm Endometrialepithelium (uterinelining) Uterus Blastocoel General Biology lectured by Han-Jia Lin 34 – Theinnercellmass isaclusterofcellsatone endoftheblastocyst Primitivestreak Migrating cells (mesoderm) General Biology lectured by Han-Jia Lin Innercellmass Trophoblast Endoderm Hypoblast Blastocoel YOLK 35 1 Blastocystreachesuterus. General Biology lectured by Han-Jia Lin 36 Implantation BeginningofGastrulation • Thetrophoblast cellssecretenzymesto b kd breakdownandinvadetheendometrium d i d th d ti of f uterus(ηϣጢ). • Afterimplantation,trophoblast f i l i h bl continuesto i expandandasetofextraembryonic membranes is formed isformed. • Innercellmassformaflatdiskwithepiblast and hypoblast Expandingregionof trophoblast Amnioticcavity Epiblast Hypoblast Yolksac(fromhypoblast) Expandingregionof trophoblast Maternal blood vessel Epiblast Hypoblast Extraembryonicmesoderm cells(fromepiblast) cells (from epiblast) Chorion(fromtrophoblast) Trophoblast 2 Blastocystimplants Blastocyst implants (7daysafterfertilization). General Biology lectured by Han-Jia Lin 37 LateGastrulationinhuman • Thefourextraembryonic membranes that form aroundtheembryoofamniotes(Բጢ)ނ, Բ ނ includingreptiles,birdsandmammals – Likechickembryo,cellsmoveinwardfromthe epiblastthroughaprimitivestreakandform mesodermandendoderm Allantois 4 Gastrulationhasproduceda threelayeredembryowith fourextraembryonic membranes. General Biology lectured by Han-Jia Lin 38 DevelopmentalAdaptationsofAmniotes • Embryo: y Amnion Chorion Ectoderm Mesoderm Endoderm Yolksac 3 Extraembryonicmembranes ( y ), starttoform(10–11days), andgastrulationbegins (13days). General Biology lectured by Han-Jia Lin – Thechorion (้Лጢ)functionsingasexchange – Theamnion (Բጢ* enclosestheamnioticfluid – Theyolksac(ռ៶ጢ) enclosestheyolkintheeggof reptilesandisthesiteofearlyformationofbloodin mamals – Theallantois (ֿ៶ጢ)disposesofwasteproductsin reptileeggandincorporatedintotheumbilicalcord(ᙏ )inmammals • Placenta: – Invading trophoblast – Cellsfromepiblast – Adjacent endometrum • butnotinfishandamphibians,why? 39 General Biology lectured by Han-Jia Lin 40 Figure 47.13a Neural folds Organogenesis • Cellmovement Frog neurulation – Gastrulation Æ massmovement – OrganogenesisÆ localmovement – MorphogenesisÆ Æ moveandchangeofshape(animalonly) • Duringorganogenesis,variousregionsofthegermlayers developintorudimentaryorgans – Ex:theneurulationÆ brainandspinalcord(ૉᡎ) – Notochord(ૉ)Æ startfromdorsalmesoderm(arod) – Neuralplate(ઓ݈)Æ ectodermabovethenotochord, i d d b i li inducedbysignalingmoleculesfrommesodermalcellsand l l f d l ll d others • Neuraltube(ઓᆅ)Æ Neural tube (ઓᆅ) Æ rolledfromneuralplateÆ rolled from neural plate Æ central central nervoussystem(brainandspinalcord) General Biology lectured by Han-Jia Lin 1 mm Neural plate Notochord Ectoderm Mesoderm Endoderm A h t Archenteron (a) Neural plate formation 41 Neural fold Neural fold General Biology lectured by Han-Jia Lin 42 Neural tube related cells in vertebrate development Neural plate • Neuralcrestcells (ઓૉಒझ) ( ) – Developalongtheneuraltube(ectoderm) – Migrationtoformvariouspartsoftheembryo(peripheral g p y (p p nerves,partsofteeth,skullbones,andsoon) Question: Our CNS comes from which germ layer? • Somites (ᡏ) Neural crest cells Neural crest cells (b) Neural tube formation General Biology lectured by Han-Jia Lin Neural tube – Lateraltothenotochordformsblocks(mesoderm) – MigrationofmesenchymecellsÆ vertebraeformationand musclesassociatedwith – Themesodermsplitstoformthecoelom(bodycavity) – Somitebecomeslessobviouslaterindevelopment – Notochorddisappearedbeforebirth(someleavein vertebraldisk໔ዬ) b l di k ໔ዬ) Outer layer y of ectoderm Figure 47.13b-3 43 General Biology lectured by Han-Jia Lin 44 Figure 47.13c Eye Somites Tail bud Chick neurulation • Early Earlyorganogenesisinothervertebratesissimilarto organogenesis in other vertebrates is similar to thatinthefrog SEM Neural tube Notochord Coelom • Chickneurulation Chi k l ti Æ threelayertube th l t b 1 mm Neurall N crest cells Neural tube Notochord )ઓૉಒझ* Eye Forebrain Somite Coelom E d d Endoderm Mesoderm Ectoderm Archenteron Lateral fold Heart Blood vessels Somites Somite (c) Somites Yolk stalk )ᡏ* These layers y form extraembryonic membranes. Archenteron (di (digestive ti cavity) General Biology lectured by Han-Jia Lin 45 Yolk sac Neural tube YOLK (a) Early organogenesis General Biology lectured by Han-Jia Lin (b) Late organogenesis (3 day old) Spina bifida (ૉࢊ) Organogenesis in invertebrates • A portion of the neural tube fails to develop or close properly • Themechanismsaresimilar 46 – Alsoinvolvemanycellmigrationandsignaling • Surgical repair – Themolecularsignalingpathwaysareverysimilar The molecular signaling pathways are very similar • Nerve damage Æ • Butthebodyplanisverydifferent – Ininsects,theneuraltubedevelopsalongtheventralside oftheembryo(vertebratesÆ dorsal) permanent Æ paralysis 1~2 2 per 1 1,000 000 in • 1 US General Biology lectured by Han-Jia Lin 47 General Biology lectured by Han-Jia Lin 48 Ectoderm MechanismsofMorphogenesis Neural plate • MovementofcellsÆ changeoftheshapeÆ cytoskeleton(ಒझମࢎ) k l ( झମࢎ) Microtubules • Cytoskeleton:microtubules(༾λᆅ)and y ( ) microfilaments(༾ํ) • Reorganization Reorganizationofthecytoskeletonisamajorforcein of the cytoskeleton is a major force in changingcellshapeduringdevelopment Actin filaments • Ex:inneurulation Wedge-shaped cells ུ Not only in vertebrate Not only in neuralation – microtubules microtubulesorientedfromdorsaltoventralinasheetof oriented from dorsal to ventral in a sheet of ectodermalcellshelplengthenthecellsalongthataxis Neural tube General Biology lectured by Han-Jia Lin 49 General Biology lectured by Han-Jia Lin Figure 47.15-5 50 Convergence extension in sea urchin development Convergent extension • Thecytoskeletonpromoteselongationofthe archenteron in the sea urchin embryo archenteronintheseaurchinembryo • rearrangementofcellsofatissuethatcauseitto becomenarrower(converge)andlonger(extend) Convergentextensionoccursinotherdevelopmental extension occurs in other developmental • Convergent processesÆ frogdevelopment Similar! • Th Thecytoskeletonalsodirectscellmigration(amoeboid t k l t l di t ll i ti ( b id movement) – Transmembrane glycoprotein:celladhesionmolecules – Extracellularmatrix(ECM) ( ) General Biology lectured by Han-Jia Lin 51 47.16 General BiologyFigure lectured by Han-Jia Lin 52 ProgrammedCellDeath End of Part 2 • Programmedcelldeathisalsocalledapoptosis Ask yourself…. • Atvarioustimesduringdevelopment,individualcells, setsofcells,orwholetissuesstopdevelopingandare engulfedbyneighboringcells • How many germ layers we have? • Wh Whatt different diff t in i the th gastrulation t l ti between b t sea urchin, chick and human? • For Forexample,manymoreneuronsareproducedin example many more neurons are produced in developingembryosthanwillbeneeded • What’s different in the neuron development between invertebrates and vertebrates? • Extraneuronsareremovedbyapoptosis,why? E t db t i h ? General Biology lectured by Han-Jia Lin 53 Cell fates: determination and differentiation General Biology lectured by Han-Jia Lin 54 FateMapping • Fatemapsarediagramsshowingorgansandother structuresthatarisefromeachregionofanembryo h f h f b • Determination isthetermusedtodescribethe processbywhichacellorgroupofcellsbecomes committedtoaparticularfate(beginning) • Classicstudiesusingfrogsindicatedthatcelllineagein g g g germlayersistraceabletoblastulacells • Differentiation referstotheresultingspecialization in structure and function (result) instructureandfunction(result) • How?Æ Cellsinamulticellularorganismsharethe samegenome – Differencesincelltypesistheresultoftheexpressionof differentsetsofgenes – Cytoplasmicdeterminantsandinductivesignals y p g contributetocellfatespecification General Biology lectured by Han-Jia Lin 55 General Biology lectured by Han-Jia Lin 56 Technologies for embryologists Study of C. elegans (ጕᙝ) • Dye injection Æ Æ Æ Specific marker gene • Development Developmentfinishedin3.5daywith959cellsina finished in 3 5 day with 959 cells in a worm • Cell ablation • Ablation(destruction)ofsinglecellstodetermine thestructuresthatnormallyarisefromeachcell 64-cell embryos – thelineageofeachofthe959somaticcellsisknown Blastomeres injected with dye • Question:why959cells? Larvae (b) Cell lineage analysis in a tunicate General Biology lectured by Han-Jia Lin Time affter fertilization (h hours) Figure 47.18 57 General Biology lectured by Han-Jia Lin 1 mm 58 Zygote 0 Tracing the formation of germ cells First cell division Nervous system, outer skin,, musculature Musculature, gonads Outer skin, nervous system Germ line (future gametes)) g • Germcellsarethespecializedcellsthatgiveriseto spermoreggs Musculature • ComplexesofRNAandproteinareinvolvedinthe p p specificationofgermcellfate 10 Hatching g • In InC.elegans,suchcomplexesarecalledPgranules, C elegans such complexes are called P granules persistthroughoutdevelopment,andcanbe detected in germ cells of the adult worm detectedingermcellsoftheadultworm Intestine Intestine Anus Mouth Eggs P granule protein in the gonad of adult worm Vulva POSTERIOR ANTERIOR 1.2 mm General Biology lectured by Han-Jia Lin 59 General Biology lectured by Han-Jia Lin 60 20 Pm Cytoplasmic determinants move before cell cleavage Determination by P granules 1 Newly fertilized egg • Pgranulesactascytoplasmicdeterminants,fixing g y p g germcellfateattheearlieststageofdevelopment • P Pgranulesaredistributedthroughoutthenewly granules are distributed throughout the newly fertilizedeggandmovetotheposteriorendbefore the first cleavage division thefirstcleavagedivision 2 Zygote yg prior p to first division • Witheachsubsequentcleavage,thePgranulesare partitionedintotheposteriormostcells 3 Two-cell embryo Using the same idea, the fates of all cells during C. elegans development are known… There are 131 cells die during development…. Q: How many rounds of mitosis must be done during C. elegans development? 4 Four-cell embryo General Biology lectured by Han-Jia Lin 61 Little worm, great discovery! By y using g C. elegans g as a model system, the Laureates have identified key genes regulating these processes processes. They have also shown that corresponding genes exist in higher species, including man man. General Biology lectured by Han-Jia Lin 63 http://www.nobelprize.org/nobel prizes/medici General Biology lectured by Han-Jia Lin Figure 47.20 62 AxisFormation(ᡏືԋ) • Inbilateralsymmetry(ୁٿჹᆀ)animals • Thisbodyplanexhibits – Almostsymmetry:rightleftaxis Almost symmetry: right left axis – Asymmetry:dorsalventralandanteriorposterioraxes General Biology lectured by Han-Jia Lin 64 Rotation of egg surface after fertilization in frog Establish the axis • Uponfusionoftheeggandsperm,theeggsurface rotates withrespecttotheinnercytoplasm with respect to the inner cytoplasm • Veryearlyindevelopment • Thiscorticalrotationbringsmoleculesfromonearea oftheinnercytoplasmoftheanimalhemisphereto interactwithmoleculesinthevegetalcortex – Theanteriorposterioraxisofthefrogembryois p g y determinedduringoogenesis • Thefollowingstatementsarealltrue The following statements are all true • Thisleadstoexpressionofdorsal (wheresperm entered the egg) and ventralspecific enteredtheegg)andventral specificgeneexpression gene expression – The animalvegetalasymmetryindicateswhere theanteriorposterioraxisforms h i i i f – Thedorsalventralaxisisnotdetermineduntil fertilization Confusing? General – Biology lectured by Han-Jia Lin 65 General Biology lectured by Han-Jia Lin 66 RestrictingDevelopmentalPotential Axis establishment in other animals • Ininsects – Morphogen gradientsdeterminebothAPandDV(dorsal ventral)axes • Progressiverestrictionofdevelopmentalpotentialis a general feature of development in all animals ageneralfeatureofdevelopmentinallanimals • Inchicks • Ingeneraltissuespecificfatesofcellsarefixedby thelategastrulastage – gravityisinvolvedinestablishingtheAPaxis gravity is involved in establishing the A P axis – Later,pHdifferencesbetweenthetwosidesofthe bl t d blastoderm establishtheDVaxis t bli h th D V i p p ( ) determinea • HansSpemann’sexperiments(1938)Æ cell䇻sdevelopmentalpotential(rangeofstructures g ) towhichitcangiverise) • Inmammals,experimentssuggestthatorientationof theeggandspermnucleibeforefusionmayhelp establishembryonicaxes • Embryonicfatesareaffectedbydistributionof determinants and the pattern of cleavage determinantsandthepatternofcleavage • OnceAPandDVaxesfixed,LRaxisisfixed! General Biology lectured by Han-Jia Lin 67 General Biology lectured by Han-Jia Lin 68 Figure 47.22-2 EXPERIMENT Control egg (dorsal view) Loss of totipotent Experimental egg (side view) 1a Control 1b Experimental group group g p Gray crescent Gray crescent • Th Thefirsttwoblastomeres fi t t bl t ofthefrogembryoare f th f b totipotent (candevelopintoallthepossiblecell t types) ) Thread • Inmammals,embryoniccellsremaintotipotentuntil the8cellstage,muchlongerthanotherorganisms 2 – 16cell 16 cellstageÆ stage Æ trophoblast orinnercellmass or inner cell mass determined RESULTS Normal General Biology lectured by Han-Jia Lin • Cellfatecommitmentisirreversiblefromwhen? Belly piece Normal 69 General Biology lectured by Han-Jia Lin 70 Not only did a transplanted dorsal lip of the bl t blastopore continue ti to t be b a blastopore bl t lip, li it also l triggered gastrulation of the surrounding tissue! InductiveSignals • Asembryoniccellsacquiredistinctfates,they influencefatesofeachotherbyinduction fl f f h h b d p g Æ organizerexperminent g p • Ex1:SpemannandMangold EXPERIMENT Dorsall lip D li off blastopore – Thedorsallipfunctionsasanorganizeroftheembryobody plan inducing changes in surrounding tissues to form plan,inducingchangesinsurroundingtissuestoform notochord,neuraltube,andsoon Pigmented gastrula (donor embryo) • Ex2:limbformationinvertebrate Ex2: limb formation in vertebrate RESULTS Primary embryo Secondary (induced) embryo Nonpigmented gastrula (recipient embryo) Now, we know dorsal lip region inhibit a “ “determinant”, BMP-4 Primary structures: Neural tube Notochord Secondary structures: Notochord (pigmented cells) Neural tube ( (mostly tl nonpigmented i t d cells) ll ) Figure 47.23 General Biology lectured by Han-Jia Lin 71 General Biology lectured by Han-Jia Lin 72 FormationoftheVertebrateLimb Pattern formation of chick wings • Inductivesignalsplayamajorroleinpattern f formation,developmentofspatialorganization i d l f l • Thewingsandlegsofchicks,likeallvertebratelimbs, beginasbumpsoftissuecalledlimbbuds • Theembryoniccellsinalimbbudrespondto positionalinformationindicatinglocationalongthree axes • Themolecularcuesthatcontrolpatternformationare p calledpositionalinformation • This Thisinformationtellsacellwhereitiswithrespectto information tells a cell where it is with respect to thebodyaxes – PDaxis ((shoulder– fingertip) g p) – APaxis (Thumblittle (Thumb littlefinger) finger) – DVaxis (Knucklepalm) (Knuckle palm) • Itdetermineshowthecellanditsdescendents respondtofuturemolecularsignals • Thewingsandlegsofchicks,likeallvertebratelimbs, begin as bumps of tissue called limb buds beginasbumpsoftissuecalledlimbbuds General Biology lectured by Han-Jia Lin 73 2 Digits A t i Anterior Ventral Distal Proximal Dorsal Figure 47.24b Posterior General Biology lectured by Han-Jia Lin 74 Two organizers in chick’s limb buds ZPAproducesaninductivesignal • AER(apicalectodermal ridge) • TissuetransplantationexperimentsÆ ZPAproduces positionalinformationindicating䇾posterior䇿 l f d 䇾 䇿 Anterior Limb bud – thickened thickenedectodermat ectoderm at thebud’stip • ZPA ZPA(zoneofpolarizing ( f l ii activity) – mesodermal tissue under the ectoderm undertheectoderm wheretheposterior side of the bud is sideofthebudis attachedtothebody General Biology lectured by Han-Jia Lin AER ZPA Posterior Limb buds • ZPAsecretÆ Sonichedgehog(aninductivesignalfor g g( g limbdevelopment) – Similar SimilartoDrosophilaHedgehoggene(Hox):Thisgene to Drosophila Hedgehog gene (Hox): This gene familyalsoplayrolesofpatternformationinmanyanimals 50 Pm RESULTS EXPERIMENT Apical ectodermal ridge (AER) Anterior ZPA Figure 47.24a 3 4 75 Donor limb bud Posterior General Biology lectured by Han-Jia Lin New ZPA Host limb bud 4 3 22 4 3 76 Cilia (ᠼЛ) and Cell Fate Kartagener’s syndrome • Two types of cilia: motile or nonmotile • Ciliary Cili f function ti iis essential ti l ffor h human embryo b • Described by Dr. Kartagener in 1923 • Motile cilia • ~25% 25% was PCD ((primary i ciliary ili d ki dyskinesia) i ) – Propel fluid over cell surface or in sperm • Nasal sinuses and – Play Pl roles l iin lleft-right ft i ht specification ifi ti bronchi infection – Kartagener’s syndrome H Heart t • Male infertility • Monocilia (nonmotile cilia) Liver p Spleen • Situs Sit inversus i – A Act as antenna to receive i signal i l (f (from sonic i hedgehog….) Stomach 1/10,000 chance • ~1/10,000 – play roles in normal kidney development General Biology lectured by Han-Jia Lin Lungs 77 General Biology lectured by Han-Jia Lin Large intestine Normal location of internal organs Location in situs inversus End of Part 3 End of the class Ask yourself… • The key concepts which you have learned in • How embryologists establish fate map? • Part 1 • What is cytoplasmic determinants? How they work? • Part 2 78 • What is organizers? • How cilia determines cell fates? General Biology lectured by Han-Jia Lin • Part 3 79 General Biology lectured by Han-Jia Lin 80