Cellular Processes in Segmentation

Section I: The Diversity of Segmentation : Segmentation: A Zoological Concept of Seriality Segments and Segmentation Segments and Series Ontogeny of Seriality and Segmentation Theories on the Evolution of Seriality and Segmentation How Often Did Segments Evolve?Problems with Structural Definitions of a Segment Problems with Ontogenetic Definitions of a Segment Structural and Ontogenetic Segment Definitions Lead to Paradoxes Segments Do Not Form Spatial and Differential Units Simple Anomalies Disturb the Pattern of Segmentation Criticism of the Term “Segment”Acknowledgments References : Diversity in Segmentation Mechanisms Introduction The Sequence of Segment Formation Embryonic or Post-Embryonic Segmentation Simultaneous or Sequential Segmentation Cyclical Processes in Segmentation Proliferation versus Cell Rearrangement As Drivers of Segment Formation Types of Cells in Segmentation Processes Commonalities in Segmentation Processes: Are There Any?References Section II: Cellular Mechanisms of Segmentation : Cell Division, Movement, and Synchronization in Arthropod Segmentation Introduction Segmentation and Elongation: The Evolving Roles of Cell Division and Cell Rearrangement The Role of Cell Division Case Studies Support a New Model for the Role of Cell Division in the Posterior Thamnocephalus Oncopeltus Tribolium What Have These Case Studies Revealed?The Growth Zone Typically Requires Mitosis But Only at Low Rates The Anterior Growth Zone Functions As a Transition Zone in Segmental Specification Cell Division Is Highly Regulated and Regionalized in Both the Growth Zone and Trunk The Role of Cell Rearrangement Cell Rearrangements from Diverse Taxa Have Some Common Features Convergent Extension Drives Elongation in Drosophila Elongation in Drosophila Occurs Primarily by Junctional Remodeling Intra- and Intercellular Effectors of Cell Movements Are Polarized in Drosophila Pair-Rule Genes Drive Periodic Expression of the Toll Receptors Required for Convergent Extension Cell Rearrangements in Sequentially Segmenting Arthropods: The Tribolium Model Live Imaging Shows Clear Convergent Extension in the Tribolium Germband How Do Posterior Cells in Tribolium Converge and Extend?Role of Pair-Rule Genes in Elongation in Tribolium Role of Toll Receptors in Tribolium Polarized Effectors of Cell Movement Have Not Been Documented in Tribolium Possible Hypotheses for Mechanisms of Convergent Extension in Tribolium Synchronizing Cell Division, Cell Rearrangements, and Cell Fate Summary Acknowledgments References : Cellular and Molecular Mechanisms of Segmentation in Annelida Introduction to the Annelida Segmentation in Annelids An Overview of Annelid Development Early Embryonic Development Cell Fate Maps: Trochophore Larvae and Direct Development Segmentation of the Trunk Segment Development in Owenia Segment Development in Platynereis dumerilii Segment Development in Capitella teleta Segment Development in Tubifex tubifex Molecular Basis of Annelid Segmentation Evolutionary Remarks References : Progenitor Cells in Vertebrate Segmentation Segmentation in Vertebrates The Clock and Wavefront Model of Somitogenesis Neuromesodermal Progenitors As the Cellular Source of Vertebrate Segments Do All Somites along the Anterior–Posterior Axis Come from NMPs?Are NMPs Stem Cells?The Transcription Factor Brachyury Links NMP Maintenance with Segmentation Signaling Pathways Coordinating Mesoderm Induction and Segmentation Induction of Paraxial/Somite Fate in NMP-Derived Mesoderm Termination of Somitogenesis Progenitor Cell Behaviors That Influence the Synchronization of Cycling Gene Expression NMPs As a Development Module Affecting Evolutionary Change in Segment Number and Body Length Do NMPs Exist Outside the Vertebrate Clade?Conclusions References : Teloblasts in Crustaceans Introduction Formation of the Germ Disc Germ Band Growth Evolution of the Stereotyped Division Pattern Anomaly of Cell Shapes and Behavior Hierarchy of Germ Layers Segmentation Short and Long Germ Development Segment Morphogenesis Cell Lineage and Cell Fate Homology Issues Perspectives Acknowledgments References : Segmentation in Leeches Introduction Segmentation in the Helobdella Body Plan Boundary-Driven versus Lineage-Driven Segmentation An Axial Posterior Growth Zone (PGZ) Originates from the D Quadrant in Helobdella and Other Clitellate Annelids The Leech PGZ Provides a Highly Simplified and Experimentally Accessible Example of Axial Growth and Patterning Evolutionary Antiquity of the M Teloblasts Kinship Groups Are Well Conserved within Each Lineage, But Heterogeneous in Terms of Cell-Type Composition and Spatial Distribution Kinship Groups Are Not Clones The O–P Equivalence Group Grandparental Stem Cell Lineages Expression Patterns of Drosophila Segmentation Gene Homologs Spatiotemporal Registration of Blast Cell Clones Segment Identities and the Paradoxical Specification of Regional Differences along the Anterior–Posterior Axis The “Leech Perspective” on the Counting Problem in Segmentation Genesis of Endoderm from a Syncytial Yolk Cell Mesoderm As a Primary Driver of Segmental Patterning in Leeches Summary and Conclusions References : Segmentation in Motion Introduction Live Imaging to Study Sequential Segmentation in Vertebrates Cell Dynamics during Somite Border Formation Real-Time Imaging of the Segmentation Clock The Migratory Behavior of the Presomitic Mesoderm Cells Live Imaging during Annelid Sequential Segmentation Live Imaging during Arthropod Sequential Segmentation Conclusions References Section III: Beyond Segmentation : Segmental Traits in Non-Segmented Bilaterians Background What Is Segmental?Xenacoelomorpha Deuterostomia Hemichordata (Acorn Worms)Echinodermata (Sea Urchins, Sea Stars, and Others)Cephalochordata (Lancelets or Amphioxi)Tunicata (Sea Squirts and Salps)Ecdysozoa Nematoda (Round Worms)Nematomorpha (Horsehair Worms)Priapulida (Penis Worms)Kinorhyncha (Mud Dragons)Loricifera (Girdle Wearers)Tardigrada (Water Bears)Onychophora (Velvet Worms)Spiralia Chaetognatha (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)Discussion Acknowledgments References : Axial Regeneration in Segmented Animals: A Post-Embryonic Reboot of the Segmentation Process Introduction The Phylogenetic Distribution of Regeneration Common Aspects of Animal Regeneration Wound Healing Cell Reorganization and Blastema Formation Cell Differentiation and Morphogenesis Regeneration in Annelids Stages of Axial Regeneration Wound Healing Cell Migration Cell Proliferation Cellular Sources and Development of the Blastema Neural Regeneration Muscle Regeneration Segmentation Segmentation during Posterior Regeneration Segmentation during Anterior Regeneration Morphallactic Processes Concluding Remarks Acknowledgments References Index