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Cellular Processes in Segmentation

Section I: The Diversity of Segmentation: Segmentation: A Zoological Concept of SerialitySegments and SegmentationSegments and SeriesOntogeny of Seriality and SegmentationTheories on the Evolution of Seriality and SegmentationHow Often Did Segments Evolve?Problems with Structural Definitions of a SegmentProblems with Ontogenetic Definitions of a SegmentStructural and Ontogenetic Segment Definitions Lead to ParadoxesSegments Do Not Form Spatial and Differential UnitsSimple Anomalies Disturb the Pattern of SegmentationCriticism of the Term “Segment”AcknowledgmentsReferences: Diversity in Segmentation MechanismsIntroductionThe Sequence of Segment FormationEmbryonic or Post-Embryonic SegmentationSimultaneous or Sequential SegmentationCyclical Processes in SegmentationProliferation versus Cell Rearrangement As Drivers of Segment FormationTypes of Cells in Segmentation ProcessesCommonalities in Segmentation Processes: Are There Any?ReferencesSection II: Cellular Mechanisms of Segmentation: Cell Division, Movement, and Synchronization in Arthropod SegmentationIntroductionSegmentation and Elongation: The Evolving Roles of Cell Division and Cell RearrangementThe Role of Cell DivisionCase Studies Support a New Model for the Role of Cell Division in the PosteriorThamnocephalusOncopeltusTriboliumWhat Have These Case Studies Revealed?The Growth Zone Typically Requires Mitosis But Only at Low RatesThe Anterior Growth Zone Functions As a Transition Zone in Segmental SpecificationCell Division Is Highly Regulated and Regionalized in Both the Growth Zone and TrunkThe Role of Cell RearrangementCell Rearrangements from Diverse Taxa Have Some Common FeaturesConvergent Extension Drives Elongation in DrosophilaElongation in Drosophila Occurs Primarily by Junctional RemodelingIntra- and Intercellular Effectors of Cell Movements Are Polarized in DrosophilaPair-Rule Genes Drive Periodic Expression of the Toll Receptors Required for Convergent ExtensionCell Rearrangements in Sequentially Segmenting Arthropods: The Tribolium ModelLive Imaging Shows Clear Convergent Extension in the Tribolium GermbandHow Do Posterior Cells in Tribolium Converge and Extend?Role of Pair-Rule Genes in Elongation in TriboliumRole of Toll Receptors in TriboliumPolarized Effectors of Cell Movement Have Not Been Documented in TriboliumPossible Hypotheses for Mechanisms of Convergent Extension in TriboliumSynchronizing Cell Division, Cell Rearrangements, and Cell FateSummaryAcknowledgmentsReferences: Cellular and Molecular Mechanisms of Segmentation in AnnelidaIntroduction to the AnnelidaSegmentation in AnnelidsAn Overview of Annelid DevelopmentEarly Embryonic DevelopmentCell Fate Maps: Trochophore Larvae and Direct DevelopmentSegmentation of the TrunkSegment Development in OweniaSegment Development in Platynereis dumeriliiSegment Development in Capitella teletaSegment Development in Tubifex tubifexMolecular Basis of Annelid SegmentationEvolutionary RemarksReferences: Progenitor Cells in Vertebrate SegmentationSegmentation in VertebratesThe Clock and Wavefront Model of SomitogenesisNeuromesodermal Progenitors As the Cellular Source of Vertebrate SegmentsDo All Somites along the Anterior–Posterior Axis Come from NMPs?Are NMPs Stem Cells?The Transcription Factor Brachyury Links NMP Maintenance with SegmentationSignaling Pathways Coordinating Mesoderm Induction and SegmentationInduction of Paraxial/Somite Fate in NMP-Derived MesodermTermination of SomitogenesisProgenitor Cell Behaviors That Influence the Synchronization of Cycling Gene ExpressionNMPs As a Development Module Affecting Evolutionary Change in Segment Number and Body LengthDo NMPs Exist Outside the Vertebrate Clade?ConclusionsReferences: Teloblasts in CrustaceansIntroductionFormation of the Germ DiscGerm BandGrowthEvolution of the Stereotyped Division PatternAnomaly of Cell Shapes and BehaviorHierarchy of Germ LayersSegmentationShort and Long Germ DevelopmentSegment MorphogenesisCell Lineage and Cell FateHomology IssuesPerspectivesAcknowledgmentsReferences: Segmentation in LeechesIntroductionSegmentation in the Helobdella Body PlanBoundary-Driven versus Lineage-Driven SegmentationAn Axial Posterior Growth Zone (PGZ) Originates from the D Quadrant in Helobdella and Other Clitellate AnnelidsThe Leech PGZ Provides a Highly Simplified and Experimentally Accessible Example of Axial Growth and PatterningEvolutionary Antiquity of the M TeloblastsKinship Groups Are Well Conserved within Each Lineage, But Heterogeneous in Terms of Cell-Type Composition and Spatial DistributionKinship Groups Are Not ClonesThe O–P Equivalence GroupGrandparental Stem Cell LineagesExpression Patterns of Drosophila Segmentation Gene HomologsSpatiotemporal Registration of Blast Cell ClonesSegment Identities and the Paradoxical Specification of Regional Differences along the Anterior–Posterior AxisThe “Leech Perspective” on the Counting Problem in SegmentationGenesis of Endoderm from a Syncytial Yolk CellMesoderm As a Primary Driver of Segmental Patterning in LeechesSummary and ConclusionsReferences: Segmentation in MotionIntroductionLive Imaging to Study Sequential Segmentation in VertebratesCell Dynamics during Somite Border FormationReal-Time Imaging of the Segmentation ClockThe Migratory Behavior of the Presomitic Mesoderm CellsLive Imaging during Annelid Sequential SegmentationLive Imaging during Arthropod Sequential SegmentationConclusionsReferencesSection III: Beyond Segmentation: Segmental Traits in Non-Segmented BilateriansBackgroundWhat Is Segmental?XenacoelomorphaDeuterostomiaHemichordata (Acorn Worms)Echinodermata (Sea Urchins, Sea Stars, and Others)Cephalochordata (Lancelets or Amphioxi)Tunicata (Sea Squirts and Salps)EcdysozoaNematoda (Round Worms)Nematomorpha (Horsehair Worms)Priapulida (Penis Worms)Kinorhyncha (Mud Dragons)Loricifera (Girdle Wearers)Tardigrada (Water Bears)Onychophora (Velvet Worms)SpiraliaChaetognatha (Arrow Worms)Rotifera (Wheel Worms)Micrognathozoa (Jaw Animals)Gastrotricha (Hairybacks)Platyhelminthes (Flatworms)Nemertea (Ribbon Worms)Mollusca (Snails and Squids)Brachiopoda (Lamp Shells)Phoronida (Horseshoe Worms)Bryozoa (Moss Animals)DiscussionAcknowledgmentsReferences: Axial Regeneration in Segmented Animals: A Post-Embryonic Reboot of the Segmentation ProcessIntroductionThe Phylogenetic Distribution of RegenerationCommon Aspects of Animal RegenerationWound HealingCell Reorganization and Blastema FormationCell Differentiation and MorphogenesisRegeneration in AnnelidsStages of Axial RegenerationWound HealingCell MigrationCell ProliferationCellular Sources and Development of the BlastemaNeural RegenerationMuscle RegenerationSegmentationSegmentation during Posterior RegenerationSegmentation during Anterior RegenerationMorphallactic ProcessesConcluding RemarksAcknowledgmentsReferencesIndex

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