STARTSTARTFOUNDATIONSFOUNDATIONSHow-to 1How-to 1FORMATIONFORMATIONHow-to 2How-to 2SYSTEMSSYSTEMSPROBLEMSPROBLEMSBIOCHEM GENETICS CELL BIO.MOL. BIOSTEM CELLS,CLONINGREC. DNAFERTILI-ZATION 3DSTRUCTURESTEPSVIRUSESCANCERHUMANDISEASELIFELIFENERVOUSIMMUNESYSTEMSBIOLOGYFUTUREFUTURE7.0134.2.07Formation I(Principles of development)+=egg spermzygote embryoadult organismhuman ~1014 cellsfertilizationreplacementcells1timeTeratogen: Effects of thalidomide on limb formation2Normal brain Fetal Alcohol Syndrome brain3Newt limb regenerationamputation4Multiple processes directdevelopmentCell division: human embryos from 24 days (stage 11) >>> 56 days (stage 23) after fertilization5Cell type and tissue: eye/ retinal neurons6dorsalventraldorsal (back)ventral (belly)anterior(head)posterior(tail)Defining positionthe axesleft right7Defining position/pattern: segments(Ladybird beetle larva)83D structure:humanheart9Zebrafish development 1-19 hours post-fertilizationIt’s a kind of magic/ QueenWatch for:1. Cell division2. Structure10Development requiresdifferentialgene expressiontranscriptioninitiation/elongationRNA splicing/export/stabilitytranslation initiation/elongationnucleusexport to cytoplasmgene(dsDNA)Gene expression: can be regulated at any pointprotein trafficking/stability/modification11H. Sive MIT 2007See Purves 14.11Uncommitted cells(undecided)Committed/determined cells(decided)Differentiated cells(final function)Stem cellsH. Sive MIT 2007timeActivation of a fewregulatory genesActivation of manyeffector genesInput(s) 1Input(s) 212Regulatory factors actwithin or between cellsCells become different because of what they inherit.Cell with localized regulators called “determinants”asymmetriccell division+Cell type 1 Cell type 2timeH. Sive MIT 200713zygote two cell32 cellDAPI/ nucleiFluorescence/ P-granulesDeterminants: P-granules >> future germ cells in C. elegans14cells secrete an “inducer”= ligand Cells become different because their neighbors tell them to do so.timeand changestheir fatecell-cell signaling: “induction”which bindsto receptors on target cells H. Sive MIT 2007cell fate 1cell fate 215timeH. Sive MIT 2007An inducer that can induce different fatesat different concentrations is termed a“morphogen”cell type 1cell type 216high ligand concentrationlow ligand concentrationComplexity increases withdevelopmental ageIncreasing complexity of the future eye17eggetcspermone territorytwo territoriesthree territoriesfive territoriesone celltwo cells(asymmetric cell division)four cellseight cellsdeterminantinducerdeterminantsand inducersincrease complexity of the embryoH. Sive MIT 200718Each territoryhas a particulargene expressioncode and fateAssaying fate andcommitmentFrog developmentegg (0h) early blastula (4h)late blastula (8h) early neurula (16h)hatched tadpole(40h)19early neurulaearly blastulahatched tadpoleFate mapping shows what cells will becomeConclusion: labeled area is destined to become neurons in eye and brainExperiment: inject non-diffusible dye,ask what labeled area becomesH. Sive MIT 200720Fate mapping in zebrafish - what cells will become1. Inject one/few cell(s) in early embryo2. Score labeled cell positionsin older embryo21When do cells decide their fate?epidermis neuronslate blastula early neurulaearly blastulaExplant experiment: remove same relative regionculture in saline, later, assay fatesepidermisConclusion: neuronal cell fate decision is made by neurula stageH. Sive MIT 200722When do cells decide their fate?Transplant experiment: move one regionto new position, later, assay fate of transplanted regionRemove future head region from donor embryoPlace in wrong positionof host embryoResult: host embryo developstwo headsConclusion:Head region wasdetermined at timeof transplantH. Sive MIT
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