Principles of Experimental EmbryologyMajor Research QuestionsThe Embryonic EnvironmentEnvironmental Regulation of DevelopmentSeasonal PolyphenismAnthropogenic EffectsEnvironmental signals – UV radiationEnvironmental Signals - IntraspecificEnvironmental Signals - TemperatureDifferentiationCommitmentSpecification TypesAutonomous SpecificationAutonomous SpecificationAutonomous SpecificationMosaic DevelopmentSyncytial SpecificationDrosophila CleavageSyncytial Specification through Morphogen GradientsSyncytial Specification through Morphogen GradientsSyncytial Specification through Morphogen GradientsBicoid Protein = HeadBicoid ManipulationConditional SpecificationConditional SpecificationConditional SpecificationMorphogen Gradients in Conditional SpecificationMorphogen Gradients in Conditional SpecificationConditional Specification: Leg-Antenna TransplantConditional Specification: Leg-Antenna TransplantStem Cells and CommitmentStem Cell Derived Blood CellsMorphogenesis and Cell AdhesionCell InteractionsCadherin-mediated Cell AdhesionPrinciples of Experimental EmbryologyBiology 4361 – Developmental BiologySeptember 19, 2006Major Research QuestionsHow do forces outside the embryo affect its development? (Environmental Developmental Biology)How do forces within the embryo cause the differentiation of cells?(Specification, Determination, Committment)How do cells organize themselves into tissues and organs? (Morphogenesis and Cell Adhesion)The Embryonic EnvironmentWhat is the “embryonic environment”?Internal influences (e.g. intrauterine):- chemicals (e.g. maternal hormones, caffeine, nicotine)- competitors (e.g. litter-mates)Environmental regulation pathway:- external stimulation triggers signaling event in embryo- signal stimulates an embryonic pathway, usually hormonal, that changes the developmental pathway.Organisms are connected to their environmentExternal influences:- light- temperature- humidity- predators -competitors- intraspecific signalsEnvironmental Regulation of DevelopmentLight, temperature & moisture = environmental signals that produce changes in embryonic hormones.Hormones induce changes in color, reproduction, hibernation, behaviorEnvironmentally-produced changes in hormones during development can affect the adult phenotype; e.g. Bicyclus anynanaseasonal polyphenism - common in butterflies Nemoria bistriariawet season dry season wet seasondry seasonSeasonal PolyphenismNemoria arizonaria larvaeearly spring – oak catkin (flower) summer – oak twigEnvironmental signal – tannins in oak leaves (probably)- developmental response – change in cuticle morphologyAnthropogenic Effectspepper mothsIndustrial melanism(“anthro” – man)Environmental signals – UV radiationUV = mutagenic, damaging to cell and tissue development- lower wavelengths have more energy; cause more damage- developmental stages are the most sensitive!melaninMycosporine-like amino acid = sunscreenHO HONOHCOOHNHCOOHOCH3RUV exposure can induce protective mechanismsnorthern leopard frogBonellia viridis (marine echiuroid worm)♂♀Environmental Signals - Intraspecific- larvae settles on sand/rock surface = ♀- larvae settles on proboscis = ♂10 cm2 mmTherefore, signal (most likely chemical) to become ♂ is from ♀Environmental Signals - Temperature- sex determined by the egg temperature during weeks 2 & 3≤ 30° C = female≥ 34° C = maleTemperature-dependent sex determination in alligatorsDifferentiationHow does the intraembryonic environment direct cellular differentiation?Differentiation – development of cellular specializationDifferentiation is a process- preceded by several identifiable steps- commitment- specification- determinationCommitmentundifferentiated differentiatedspecification determination1. Specification – capable of differentiating autonomously when placed in a neutral environment.-reversible2. Determination – capable of differentiating autonomously evenwhen placed into another region of the embryo.- essentially irreversibleStages of cell commitment:Specification TypesI. Autonomous specificationII. Syncytial SpecificationIII. Conditional SpecificationAutonomous Specification-Cells are specification by differential distribution of cytoplasmiccomponents during cleavage of the egg and early embryo.-proteins-RNAAutonomous SpecificationTunicate (sea squirt)blastomere separationAutonomous SpecificationTunicate (sea squirt)- blastomeres are committed at a very early stage in mosaic development- each dissociated blastomerepair forms original structures-each blastomere contains positional information in the form of specific proteins and genesdissociated blastomeresMosaic Developmentdifferentiated cellmitosisearly embryolater embryoSyncytial SpecificationSyncytium – nuclear division without cell division;results in cytoplasm with many nucleiDrosophilaCleavagenuclei & cytoplasm formsyncytial blastodermFELICE FARBERSyncytial Specification throughMorphogen GradientsDrosophila eggbicoid – anterior determinantnanos – posterior determinantMaternal messages:U Irion & D St JohnsonSyncytial Specification throughMorphogen Gradientsbicoid – anteriornanos – posterior Maternal messages:Each morphogenestablishes a gradientthroughout the embryo (like a diffusion gradient)Bicoid & Nanos proteins = morphogens1:0 10:1 1:1 1:5- each region will have a distinct Bicoid:Nanos ratio- Bicoid:Nanos determines anterior-posterior identitySyncytial Specification throughMorphogen GradientsCells establish identity depending on their position in multiple gradientsbicoid – anteriornanos – posterior Maternal messages:Each morphogenestablishes a gradientthroughout the embryo (like a diffusion gradient)Bicoid Protein = HeadBicoid Manipulation= morphogen gradientConditional SpecificationConditional SpecificationCell fate depends on interactions with neighboring cellsEmbryonic cells can change fates to compensate for missing parts = regulationConditional specificationproduces Regulative DevelopmentConditional Specificationdifferentiated cellmitosisearly embryolater embryoMorphogen Gradients in Conditional SpecificationCells respond to protein concentration by turning different colors.Morphogen Gradients in Conditional SpecificationCell commitment and differentiation are programmed by various morphogen gradients.Transplants of flag “cells”shows that they retain theiridentity (nationality), but grow according to the cellsaround them.Conditional Specification: Leg-Antenna