In vitro spatiotemporal reconstruction of human skeletal muscle organogenesis

Spatiotemporal recapitulation of long-range trajectories for lineages that influence body patterning along the medio-lateral and proximal-distal axes during embryogenesis in an in vitro system remains elusive. Here we introduce a three-dimensional organoid approach, termed Gastruloids-Lateraloid-Musculoids (GLMs), to model human neural crest, lateral plate mesoderm and skeletal muscle lineage development at the forelimb level following gastrulation and during limb patterning. GLMs harvest neuro-mesodermal progenitors with the potential to establish neural and paraxial mesodermal populations, while single cell analyses and spatial transcriptomics demonstrate promotion of mesodermal lineage segregation during gastrulation and spatial recapitulation of migration events along the medio-lateral axis for vagal neural crest, hypaxial myogenesis and lateral plate mesodermal lineages. Comparative analyses to developmental atlases and adult muscle stem cell data confirm a pool of hypaxial migrating myogenic progenitors that in a niche dependent manner change their embryonic anatomical developmental program to a fetal myogenic program, thus enabling them to resist specification in a cell autonomous manner and facilitate long term in vitro expansion. GLMs model human myogenesis at the forelimb level, establish fetal muscle stem cells equivalent to those that sustain the growth phase of the embryo and provide a 3D in vitro system for investigating neural crest, early fore-gut and lateral plate mesoderm development. ### Competing Interest Statement The authors have declared no competing interest.