LE 47-7Fertilized eggFour-cell stageMorulaBlastulaLE 47-8AnteriorRightAnimal poleGraycrescentDorsalVentralLeftPosteriorBody axesEstablishing the axesFuturedorsalside oftadpolePoint ofspermentryFirstcleavageVegetalhemisphereVegetal polePoint of sperm entryAnimalhemisphere• The three layers produced by gastrulationare called embryonic germ layers– The ectoderm forms the outer layer– The endoderm lines the digestive tract– The mesoderm partly fills the space between theendoderm and ectodermVideo: Sea Urchin Embryonic DevelopmentVideo: Sea Urchin Embryonic DevelopmentLE 47-11AnimalpoleBlastoporeFilopodiapullingarchenterontipArchenteronMesenchymecellsBlastocoelFuture ectodermVegetalpoleKeyFuture mesodermFuture endodermVegetalplateBlastocoelMesenchymecellsArchenteronBlastocoelMesenchume(mesodermforms futureskeleton)50 µmMouthEctodermBlastoporeDigestive tube (endoderm)Anus (from blastopore)LE 47-23bCell lineage analysis in a tunicateWhat is the most likely problem that couldarise if you used an injected dye to trace thelineage of cells in a developing animal?• A. The dye might alter the animal’sdevelopment.• B. The dye might be toxic.• C. The dye might break down or be dilutedover time.• D. The dye might be expensive or difficult toobtain.• E. The color of the embryo might obscure thedye.LE 47-24Left (control):Fertilizedsalamander eggswere allowed todivide normally,resulting in thegray crescentbeing evenlydivided betweenthe two blastomeres.Right(experimental):Fertilized eggs wereconstricted by athread so that thefirst cleavage planerestricted the graycrescent to oneblastomere.Gray crescentGray crescentNormalBellypieceNormalThe two blastomeres werethen separated andallowed to develop.LE 47-25aNonpigmented gastrula(recipient embryo)Pigmented gastrula(donor embryo)Dorsal lip ofblastoporeLE 47-25bSecondary (induced) embryoPrimarystructures:Secondarystructures:Neural tubeNotochordNotochord (pigmented cells)Neural tube (mostly nonpigmented cells)Primary embryoMaekawa, M. et al. Development 2007;134:2751-2759Effect of U0126 and PD184352 on preimplantation developmentMaekawa, M. et al. Development 2007;134:2751-2759ERK and ELK1 are phosphorylated during mouse preimplantation developmentMaekawa, M. et al. Development 2007;134:2751-2759ERK inactivation in late two-cell-stage embryos induces developmental arrest in the G2phase, just before M phase in the four-cell stageIf I suspect Protein “X” is involved in somedevelopmental process, I can test this hypothesisby:A. Adding a drug to my experimental cells/organism that blocks “X”s function.B. Degrade the messenger RNA that encodes “X”C. Alter the DNA such that the gene for “X” isdamaged or removedD. Add antibodies to “X” that will block its functionE. All of the aboveMaekawa, M. et al. Development 2007;134:2751-2759The transcriptional program during mouse preimplantation developmentMaekawa, M. et al. Development 2007;134:2751-2759Genes whose expression profiles closely parallel the stages of embryonic developmentMaekawa, M. et al. Development 2007;134:2751-2759Cell adhesion is important for early cell division
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