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Section II: Cellular Mechanisms of Segmentation

: Cell Division, Movement, and Synchronization in Arthropod Segmentation

Lisa M. Nagy and Terri A. Williams

CONTENTS

  • 3.1 Introduction....................................................................................................40
  • 3.1.1 Segmentation and Elongation: The Evolving Roles of Cell

Division and Cell Rearrangement.......................................................40

  • 3.2 The Role of Cell Division...............................................................................41
  • 3.2.1 Case Studies Support a New Model for the Role of Cell Division

in the Posterior....................................................................................41

  • 3.2.1.1 Thamnocephalus..................................................................43
  • 3.2.1.2 Oncopeltus...........................................................................46
  • 3.2.1.3 Tribolium..............................................................................48
  • 3.2.2 What Have These Case Studies Revealed?.........................................52
  • 3.2.2.1 The Growth Zone Typically Requires Mitosis But

Only at Low Rates...............................................................52

3.2.2.2 The Anterior Growth Zone Functions As a Transition

Zone in Segmental Specification.........................................53

3.2.2.3 Cell Division Is Highly Regulated and Regionalized in

Both the Growth Zone and Trunk.......................................54

  • 3.3 The Role of Cell Rearrangement....................................................................54
  • 3.3.1 Cell Rearrangements from Diverse Taxa Have Some

Common Features...............................................................................55

  • 3.3.2 Convergent Extension Drives Elongation in Drosophila....................56
  • 3.3.2.1 Elongation in Drosophila Occurs Primarily by

Junctional Remodeling.........................................................56

3.3.2.2 Intra- and Intercellular Effectors of Cell Movements

Are Polarized in Drosophila................................................56

3.3.2.3 Pair-Rule Genes Drive Periodic Expression of the Toll

Receptors Required for Convergent Extension....................57

3.3.3 Cell Rearrangements in Sequentially Segmenting Arthropods:

The Tribolium Model..........................................................................58

3.3.3.1 Live Imaging Shows Clear Convergent Extension in

the Tribolium Germband......................................................58

3.3.3.2 Tribolium Convergent Extension Does Not Appear

to Arise from a Drosophila-Like Neighbor-Sliding Mechanism...........................................................................59

3.3.3.3 How Do Posterior Cells in Tribolium Converge and

Extend?.................................................................................59

  • 3.3.3.4 Role of Pair-Rule Genes in Elongation in Tribolium...........60
  • 3.3.3.5 Role of Toll Receptors in Tribolium....................................61
  • 3.3.3.6 Polarized Effectors of Cell Movement Have Not Been

Documented in Tribolium....................................................62

3.3.3.7 Possible Hypotheses for Mechanisms of Convergent

Extension in Tribolium.........................................................62

  • 3.4 Synchronizing Cell Division, Cell Rearrangements, and Cell Fate...............63
  • 3.5 Summary........................................................................................................64

Acknowledgments....................................................................................................65

References................................................................................................................65

 
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