Somitogenesis in Vertebrate Development

A segmented body plan is a conserved feature of all vertebrate species and is established early in embryonic development by the formation of somites, the precursors to the skeleton, musculature and dermis. These epithelialised structures are formed with a species-specific periodicity during the process of somitogenesis. Gathering evidence suggests that somitogenesis is regulated by a molecular oscillator mechanism that, together with a morphogenic gradient, stipulates when and where somites form. Mutations in key molecular players in this mechanism have been closely linked to developmental disorders and segmental malformations. It is therefore of great medical interest to elucidate the regulatory mechanisms which govern this key developmental process, much of which is still not yet fully understood. Key Concepts A segmented body plan is a conserved feature of all vertebrate species. Somitogenesis describes the periodic formation of somites, which is the first overt sign of segmentation to appear in the embryonic vertebrate body plan. The temporal periodicity of somitogenesis is thought to be regulated by a molecular oscillator mechanism termed the segmentation clock. There is emerging evidence to suggest a significant degree of conservation of the regulatory mechanisms governing somitogenesis in different vertebrate species. Some particular disease states characterised by segmentation defects have been shown to result from mutation in key Notch-regulated components of somitogenesis. Many of the mechanisms thought to regulate somitogenesis and somite boundary formation appear to be highly reliant on the Notch signalling pathway. There is a large degree of crosstalk between the Notch, Wnt and FGF signalling pathways that orchestrate somitogenesis. Future advances in our understanding of the regulatory mechanisms governing somitogenesis rely on developing mathematical models and interdisciplinary approaches to direct and cooperate with biological investigation. Keywords: vertebrate segmentation; molecular oscillations; clock; wavefront; Notch signalling; molecular crosstalk; mathematical modelling; somites