Figure 1 Key embryogenic decision points during kidney development Figure 1 | Key embryogenic decision points during kidney development. a | During gastrulation, which starts with the formation of the primitive streak, the epiblast gives rise to all three germ layers (endoderm, mesoderm, ectoderm). Patterning of the posterior primitive streak is required for the mesoderm specification. b | The posterior primitive streak gives rise to the trunk mesoderm which is patterned mediolaterally into the paraxial (closest to the neural tube and giving rise to the somites), lateral plate (furthest from the neural tube and giving rise to heart and body wall) and the intermediate mesoderm, from which the kidney and gonads arise. c | The primitive streak cells that migrate to form the most anterior portion of the intermediate mesoderm give rise to the nephric duct (mesonephric duct and Wolffian duct), which elongates caudally to form the ureteric bud, a side branch next to the metanephric mesenchyme. The ureteric bud generates the branching collecting duct network of the kidney. d | Primitive streak cells that migrate from the streak at a later time point form the posterior intermediate mesoderm, which gives rise to the metanephric mesenchyme of the permanent kidney. This population attracts the ureteric bud by producing glial-derived neurotrophic factor. The mesenchyme closest to the tips of the ureteric tree is the cap mesenchyme, which are the progenitors of the forming nephrons. Little, M. H. et al. (2016) Understanding kidney morphogenesis to guide renal tissue regeneration Nat. Rev. Nephrol. doi:10.1038/nrneph.2016.126