Vertebrate development — study of the segmentation clock All animals with a backbone, vertebrates, have repeating segments called somites. Formation of the segments, somitogenesis is coordinated by waves of expression of genes via a genetic oscillator that gives rise to a developmental clock. Health © Shutterstock Muscles and bones develop from within successive somites. The segmentation clock enables the elongation of the embryo and the successive formation of somites to occur in parallel. The segmentation clock is thought to determine the rhythmic timing and spacing of somites along the vertebrate body axis. The EU-funded SEGCLOCKDYN (Collective and cell-autonomous dynamics of the genetic oscillators of the segmentation clock in zebrafish somitogenesis) project investigated somite development in the model organism the zebrafish. Project researchers identified mutant zebrafish with changes in the period of the clock. Measurements showed that somite length varies correspondingly with the length of the period. Extension of the study of clock dynamics involved engineering a set of transgenic zebrafish to look at the oscillations of individual cells. Cells synchronised with their neighbours and slowed their oscillations when they prepared to produce more somites. Moreover, changes to waves of gene expression regulated the period of somitogenesis. Mathematical simulation and analytical physical theory were applied to the data to describe both morphological dynamics and microscopic biochemical mechanisms. This helped researchers predict new findings at different developmental levels. Tissue patterning and ultimately their organised development is determined by the level of tension within individual cells and across large groups of cells. This is dictated by a genetically encoded programme. Results from the SEGCLOCKDYN project raise the possibility that genetic oscillations may be widely used in patterning, differentiation and development of embryos. Keywords Vertebrate development, segmentation, somites, genetic oscillator, tissue patterning
