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Anat Embryol (2006) 211 (Suppl. 1): S21S30 DOI 10.1007/s00429-006-0119-8
REVIEW
Faisal Yusuf Beate Brand-Saberi
The eventful somite: patterning, fate determination and cell division in the somite
Accepted: 18 August 2006 / Published online: 26 September 2006 Springer-Verlag 2006
Abstract The segmental somites not only determine the vertebrate body plan, but also represent turntables of cell fates. The somite is initially naive in terms of its fate restriction as shown by grafting and rotation experiments whereby ectopically grafted or rotated tissue of newly formed somites yielded the same pattern of normal derivatives. Somitic derivatives are determined by local signalling between adjacent embryonic tissues, in particular the neural tube, notochord, surface ectoderm and the somitic compartments themselves. The correct spatio-temporal specication of the deriving tissues, skeletal muscle, cartilage, endothelia and connective tissue is achieved by a sequence of morphogenetic changes of the paraxial mesoderm, eventually leading to the three transitory somitic compartments: dermomyotome, myotome and sclerotome. These structures are specied along a double gradient from dorsal to ventral and from medial to lateral. The establishment and controlled disruption of the epithelial state of the somitic compartments are crucial for development. In this article, we give a synopsis of some of the most important signalling events involved in somite patterning and cell fate decisions. Particular emphasis has been laid on the issue of epithelio-mesenchymal transition and dierent types of cell division in the somite.
Keywords Dermomyotome Fate determination Cell division Somite patterning
Introduction
The segmented body plan of vertebrates is realized early during embryonic development by the formation of
somites that bud o as cubes of mesenchymal tissue from the unsegmented paraxial mesoderm on either side of the neural tube. The somites form a metameric pattern during embryonic development determining the appropriate arrangement of segmentally arranged structures like vertebral column, ribs, dorsal root ganglia, spinal nerves and blood vessels.
Somites have captured the attention of a number of life scientists that have been fascinated by not just the precision and timing of somitogenesis but also by the events that follow marked by the maturation and differentiation of the somites and the derivation of a multitude of cell lineages. The latter has been studied especially in the avian embryos (Christ et al. 1974, 1977; Huang and Christ 2000; Huang...