title: An analysis of segmentation dynamics throughout embryogenesis in the centipede Strigamia maritima.
abstract: BACKGROUND
  Most segmented animals add segments sequentially as the animal grows. In vertebrates, segment patterning depends on oscillations of gene expression coordinated as travelling waves in the posterior, unsegmented mesoderm. Recently, waves of segmentation gene expression have been clearly documented in insects. However, it remains unclear whether cyclic gene activity is widespread across arthropods, and possibly ancestral among segmented animals. Previous studies have suggested that a segmentation oscillator may exist in Strigamia, an arthropod only distantly related to insects, but further evidence is needed to document this.
  
  
  RESULTS
  Using the genes even skipped and Delta as representative of genes involved in segment patterning in insects and in vertebrates, respectively, we have carried out a detailed analysis of the spatio-temporal dynamics of gene expression throughout the process of segment patterning in Strigamia. We show that a segmentation clock is involved in segment formation: most segments are generated by cycles of dynamic gene activity that generate a pattern of double segment periodicity, which is only later resolved to the definitive single segment pattern. However, not all segments are generated by this process. The most posterior segments are added individually from a localized sub-terminal area of the embryo, without prior pair-rule patterning.
  
  
  CONCLUSIONS
  Our data suggest that dynamic patterning of gene expression may be widespread among the arthropods, but that a single network of segmentation genes can generate either oscillatory behavior at pair-rule periodicity or direct single segment patterning, at different stages of embryogenesis.
authors.affiliation: Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. cb508@cam.ac.uk.
authors.forename: Carlo
authors.initials: C
authors.lastname: Brena
authors.forename: Michael
authors.initials: M
authors.lastname: Akam
mesh_terms: D000818:Animals; D060829:Arthropod Proteins / Q000235:genetics; D001181:Arthropods / Q000196:embryology* / Q000235:genetics*; D001683:Biological Clocks / Q000235:genetics; D019521:Body Patterning / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D047108:Embryonic Development / Q000235:genetics; D005091:Exons; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics; D017403:In Situ Hybridization; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D015398:Signal Transduction
chemical_list: D060829:Arthropod Proteins; D018076:DNA, Complementary; D018398:Homeodomain Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C064045:delta protein