A double segment periodicity underlies segment generation in centipede development.
The number of leg-bearing segments in centipedes varies extensively, between 15 and 191, and yet it is always odd. This suggests that segment generation in centipedes involves a stage with double segment periodicity and that evolutionary variation in segment number reflects the generation of these double segmental units. However, previous studies have revealed no trace of this. Here we report the expression of two genes, an odd-skipped related gene (odr1) and a caudal homolog, that serve as markers for early steps of segment formation in the geophilomorph centipede, Strigamia maritima. Dynamic expression of odr1 around the proctodaeum resolves into a series of concentric rings, revealing a pattern of double segment periodicity in overtly unsegmented tissue. Initially, the expression of the caudal homolog mirrors this double segment periodicity, but shortly before engrailed expression and overt segmentation, the intercalation of additional stripes generates a repeat with single segment periodicity. Our results provide the first clues about the causality of the unique and fascinating "all-odd" pattern of variation in centipede segment numbers and have implications for the evolution of the mechanisms of arthropod segmentation.
University Museum of Zoology, Downing Street, Cambridge CB2 3EJ, United Kingdom. adc36@cam.ac.uk
Ariel D
AD
Chipman
Wallace
W
Arthur
Michael
M
Akam
D000818:Animals; D001181:Arthropods / Q000033:anatomy & histology / Q000196:embryology*; D001483:Base Sequence; D019521:Body Patterning / Q000502:physiology*; D017931:DNA Primers; D029721:Drosophila Proteins; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology / Q000196:embryology; D018507:Gene Expression Regulation, Developmental; D017344:Genes, Insect / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism; D017403:In Situ Hybridization; D008954:Models, Biological; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000378:metabolism
D017931:DNA Primers; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D014157:Transcription Factors; C084564:cad protein, Drosophila; C106185:engrailed homeobox proteins