Somitogenesis and spatio-temporal scales (A) A schematic representation of somitogenesis at the organ, multicellular and single cell levels. The tightly controlled periodic development of somites is underpinned by the intercellular coupling of transcription by Notch signalling. The coupling strength is in turn influenced by trafficking in both the signal sending and receiving cells. The process of somitogenesis also depends on reading the gradients of Wnt, FGF and opposing RA by single cells. (B) The time and length scales of endosome-based processes in a developing organism schematically represented to emphasise the scaling required in imaging techniques to simultaneously view local, high resolution interactions and dynamics as well as larger, emergent processes.