Single-cell transcriptomics of human embryos identifies multiple sympathoblast lineages with potential implications for neuroblastoma origin


A number of congenital and cancer-related pathologies originate in human embryos within the sympathoadrenal and aorta-gonad-mesonephros (AGM) regions, where adrenal glands, sympathetic ganglia, hematopoietic cells, kidneys and other tissues develop from the neural crest and mesodermal lineages 1-4. Although mouse models provide detailed and experimentally validated knowledge of developmental mechanisms, differences between mouse and human development might preclude understanding of some disorders. For instance, elucidating the human-specific aspects of development might be critical for future treatment of pediatric cancers including neuroblastoma. Catecholaminergic cells in the sympathetic chain and suprare-nal ganglia (SRG) originate from neural crest cells migrating ven-trally toward the dorsal aorta 5,6. In parallel with this, controlled by a different mechanism, preganglionic visceral motor nerves bring nerve-associated neural crest-like Schwann cell precursors (SCPs) into the area during adrenocortical development to generate chro-maffin cells 7,8. Thus, two different but complementary developmental mechanisms and transitions contribute to the diversity of cell types in the mature sympathoadrenal system. The diversity of progenitors and transitions might be recapitulated in some solid tumors associated with the adrenal medulla or sympathetic ganglia, namely paraganglioma, pheochromocytoma and neuroblastoma 9-11. Neuroblastoma is a pediatric cancer, resulting in approximately 15% of total cancer-related deaths in children between the ages of 0 and 4 years old 12,13. These tumors commonly emerge near the adrenal gland and are characterized by high inter-and intrapatient heterogeneity 13,14. Next to the developing adrenal glands and dorsal aorta, the AGM region generates primordia of the adrenal cortex, kidneys, gonads and liver, initiated by the intermediate mesoderm 15-17. The dorsal aorta hosts hematopoietic progenitors that appear before hemato-poietic events in the liver 18-20 (Supplementary Note). Being inter-mixed within the sympathoadrenal and AGM areas, diverse neural crest-and mesoderm-derived cell types influence each other by inducing new cell states and fates. Knowledge of transitory states within the context of the entire reconstructed tree of cellular differentiation in human embryos is Characterization of the progression of cellular states during human embryogenesis can provide insights into the origin of pedi-atric diseases. We examined the transcriptional states of neural crest-and mesoderm-derived lineages differentiating into adrenal glands, kidneys, endothelium and hematopoietic tissue between post-conception weeks 6 and 14 of human development. Our results reveal transitions connecting the intermediate mesoderm and progenitors of organ primordia, the hema-topoietic system and endothelial subtypes. Unexpectedly, by using a combination of single-cell transcriptomics and lineage tracing, we found that intra-adrenal sympathoblasts at that stage are directly derived from nerve-associated Schwann cell precursors, similarly to local chromaffin cells, whereas the majority of extra-adrenal sympathoblasts arise from the migratory neural crest. In humans, this process persists during several weeks of development within the large intra-adrenal ganglia-like structures, which may also serve as reservoirs of originating cells in neuroblastoma. NATuRE GENETIcS |

Nature Genetics