Chapter category: Development
Avian Somitogenesis: Translating Time and Space into Pattern
Somitogenesis
Edited by: Miguel Maroto and Neil WhittockISBN: 978-0-387-09605-6
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Chapter authors:
Beate Brand-Saberi, Stefan Rudloff and Anton J. Gamel
Vertebrates have a metameric bodyplan that is based on the presence of paired somites. Somites develop from the segmental plate in a cranio-caudal sequence. At the same time, new material is added from Hensen’s node, the primitive streak and the tail bud. In this way, the material residing in the segmental plate remains constant and comprises 12 prospective somites on each side. Prospective segment borders are not yet determined in the caudal segmental plate. Prior to segmentation, the cranial segmental plate undergoes epithelialization, which is controlled by signals from the neural tube and ectoderm. The bHLH transcription factor Paraxis is critically involved in this process. Formation of a new somite from the cranial end of the segmental plate is a highly controlled process involving complex cell movements in relation to each other. Hox genes specify regional identity of the somites and their derivatives. In the chicken a transposition of thoracic into cervical vertebrae has occurred as compared to the mouse. Transcription factors of the bHLH and homeodomain type also specify the cranio-caudal polarity and that of particular cell groups within the somites. According to segmentation models, somitogenesis is under the control of a “segmentation clock” in combination with a morphogen gradient. This hypothesis has recently found support from molecular data, especially the cycling expression of genes such as cHairy1 and Lunatic Fringe, which depend on the Notch/Delta pathway of signal transduction. FGF8 has been described to be distributed along a cranio-caudal gradient. The first oscillating gene described shown to be independent of Notch is Axin2, encoding a negative regulator of the canonical Wnt pathway and a target of Wnt3a. Wnt3a and Axin2 show a similar distribution as FGF8 with high levels in the tailbud. The chick embryo has recently become accessible to molecular approaches such as overexpression by electroporation and RNA interference which can be expected to help elucidating some of the still open questions concerning somitogenesis.
Beate Brand-Saberi
Institute for Anatomy and Cell Biology
Stefan Rudloff
Anton J. Gamel
Additional chapters from this book:
Old wares and new: Five Decades of Investigation of Somitogenesis in Xenopus laevis
Duncan Sparrow
Somites are regular repeated structures formed in pairs on either side of the anterior-posterior axis of developing vertebrate embryos which give rise to all skeletal muscle of the body, the axial...
Role of Delta-Like-3 in Mammalian Somitogenesis and Vertebral Column Formation
Gavin Chapman and Sally Dunwoodie
Somitogenesis is a term that encompasses somite formation, patterning and differentiation and it is a process that is fundamental to the formation of the axial skeleton in vertebrates. Notch signallin...
Genetic analysis of somite formation in laboratory fish models
Christoph Winkler and Harun Elmasri
The repeated appearance of somites is one of the most fascinating aspects of vertebrate embryogenesis. Recent studies identified complex regulatory circuits that provide the molecular basis for the “c...
Formation and Differentiation of Avian Somite Derivatives
Bodo Christ and Martin Scaal
During somite maturation, the ventral half of the epithelial somite disintegrates into the mesenchymal sclerotome, whereas the dorsal half forms a transitory epithelial sheet, the dermomyotome, lying ...
bHLH Proteins and Their Role in Somitogenesis
Miguel Maroto, Tadahiro Iimura, J. Kim Dale and Yasumasa Bessho
The most obvious manifestation of the existence of a segmented, or metameric, body plan in vertebrate embryos is seen during the formation of the somites. Somites are transient embryonic structures fo...
Mouse Mutations Disrupting Somitogenesis and Vertebral Patterning
Kenro Kusumi, William Sewell and Megan L. O'Brien
The mouse was one of the first model organisms used in genetic analysis, beginning in 1902 with the studies of inheritance carried out by William E. Castle, Director of the Bussey Institute at Harvard...
Avian Somitogenesis: Translating Time and Space into Pattern
Beate Brand-Saberi, Stefan Rudloff and Anton J. Gamel
Vertebrates have a metameric bodyplan that is based on the presence of paired somites. Somites develop from the segmental plate in a cranio-caudal sequence. At the same time, new material is added fro...
Defective Somitogenesis and Abnormal Vertebral Segmentation in Man
Peter D. Turnpenny
In recent years molecular genetics has revolutionized the study of somitogenesis in developmental biology and advances that have taken place in animal models have been applied successfully to human di...
Mesp‑Family Genes are Required for Segmental Patterning and Segmental Border Formation
Yumiko Saga and Yu Takahashi
Elaborate somite patterning is based on the dynamic gene regulation within the presomitic mesoderm (PSM) derived from the primitive streak and tailbud in the later stage embryo. Notch signaling and th...
