By the end of the cleavage stage, theembryo is a blastula (a hollow ball ofcells)Blastomeres BlastocoelBlastomeres look very similar to each other (except for the yolk content)How much do blastomeres “know”about their final fate?Groups:Suggest an experiment that will testwhether a particular cell/group of cellswill always end up in the sametissue/organ.Lineage tracingFig. 1.9Fate map of a blastula has 3 majorsubdivisions: future ectoderm, futuremesoderm and future endodermThe three germ layers - common toalmost all animals (the triploblasticanimals)• Ectoderm• Mesoderm• Endoderm2.16 Major evolutionary divergences inextant animalsThe purpose of gastrulation:To place cells in their proper locations wherethey will form tissues and organs of the adultorganism.On the general level: to place the germ layers intheir proper positions.It is not birth, marriage, or death, butgastrulation, which is truly the mostimportant time in your life. Lewis WolpertmuscleectoderminnermostgutendodermmiddleneuralsystemmesodermouterTissue thatderivesfrom thisgerm layerGerm layerPositionaftergastrulationIndividual index card activity:Re-arrange this table, so that the germ layers andtheir derivatives will be positioned correctly.The genetics of dorso-ventralaxis specification inDrosophilaWild-typelarvaDorso-ventralspecification mutantlarvadpp-ThoraxThe segmented body plan of the flySuperficial cleavage in Drosophila embryoPole(germ)cellsSyncytialblastodermCellular blastodermFate map of Drosophila blastulaInvaginating mesodermal cells visualizedusing antibodies against Twist proteinHow the dorso-ventral cell fates arespecified?Different nuclear concentrations of thematernally deposited transcriptionfactor Dorsal determine the differentfates along the D/V axisDifferent genes are activated bydifferent concentrations of DorsalproteinDorsal sideVentral sidedpp (dorsal epidermis)msh(dorsal mesoderm,inside)ind (lateral ectoderm)vnd(neurogenic ectoderm)Oogenesis15 nurse cells+the oocyte (germ)Follicle cells (somatic)EggchamberDorso-ventral axis specification:localization of GurkengurkenmRNAGurkenproteinGenerating dorso-ventral polarity inDrosophila oocyte (part 1)Generating dorso-ventral polarity inDrosophila oocyte (part 2)MyD88MammalsNF-!BI!BIRAK4ATPTRAF-6IKKComplexCytokinePeptidoglycanTLR4CD14, MD-2ComplexTollTubePelleATPDrosophilaMyD88Dl/DifCactusDrosomycin DiptericinIKKComplexTAK1ImdDreddN-RelishC-RelishGr(+)Bacteria/FungiReceptors, Serpins, Proteases and SpätzlePGRP-LCGr(-) BacteriaPGRP-LECleavageMaternal dorso-ventral cascadegenerates the nuclear gradient of thetranscription factor dorsalThe Dorsal and Ventral signaltransduction cascades: fill in