Segmentation in Leeches

David A. Weisblat and Christopher ). Winchell

CONTENTS

  • 7.1 Introduction..................................................................................................153
  • 7.2 Segmentation in the Helobdella Body Plan..................................................155
  • 7.3 Boundary-Driven versus Lineage-Driven Segmentation..............................155
  • 7.4 An Axial Posterior Growth Zone (PGZ) Originates from the

D Quadrant in Helobdella and Other Clitellate Annelids............................158

7.5 The Leech PGZ Provides a Highly Simplified and Experimentally

Accessible Example of Axial Growth and Patterning..................................159

  • 7.6 Evolutionary Antiquity of the M Teloblasts.................................................161
  • 7.7 Kinship Groups Are Well Conserved within Each Lineage, But Heterogeneous in Terms of Cell-Type Composition and

Spatial Distribution.......................................................................................162

  • 7.8 Kinship Groups Are Not Clones...................................................................162
  • 7.9 The О-P Equivalence Group........................................................................164
  • 7.10 Grandparental Stem Cell Lineages...............................................................165
  • 7.11 Expression Patterns of Drosophila Segmentation Gene Homologs.............167
  • 7.12 Spatiotemporal Registration of Blast Cell Clones........................................168
  • 7.13 Segment Identities and the Paradoxical Specification of Regional

Differences along the Anterior-Posterior Axis............................................170

  • 7.14 The “Leech Perspective” on the Counting Problem in Segmentation..........172
  • 7.15 Genesis of Endoderm from a Syncytial Yolk Cell.......................................173
  • 7.16 Mesoderm As a Primary Driver of Segmental Patterning in Leeches.........174
  • 7.17 Summary and Conclusions...........................................................................175

References..............................................................................................................176

 
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