Neural crest cells contribute to craniofacial formation by differentiating into skeletogenic mesenchyme and neuro-glial lineages. Using Smart-seq2 single-cell transcriptomics, we show that mesenchymal fate commitment correlates specifically with the expression of rRNA-modifying and ribosome assembly factors, rather than structural ribosomal proteins. Notably, EMG1 and NHP2 introduce key post-transcriptional modifications into 18S rRNA, including m¹acp³ψ at U1248, which requires TSR3 for final maturation. Disrupting NHP2 or TSR3 in vitro and in vivo perturbs cranial neural crest differentiation; post-migratory temporal knockout of Polr1a or Polr1c also causes craniofacial malformations. These findings align with cell type-specific m¹acp³ψ levels during neural crest differentiation. Given the neural crest contribution to neuroblastoma, we analyze patient data to find that elevated ribosomal control and rRNA-modifying proteins predict poorer outcomes. Complementary experiments in neuroblastoma cell lines reveal functional roles for TSR3 and WDR74 in mesenchymal-like tumor states. Together, our results link rRNA modifications and ribosome assembly to fate decisions, suggesting ribosomal heterogeneity shapes both normal development and tumor progression. Neural crest cells differentiate into skeletogenic mesenchyme and neuro-glial lineages, thereby contributing to craniofacial formation. Here, single-cell analysis of cranial neural crest shows that specific rRNA modification and ribosome assembly factors contribute to skeletogenic fate. Their disruption causes craniofacial defects, while high levels in neuroblastoma predict poor survival.

Friedreich's ataxia (FRDA) is an inherited neurodegenerative disorder caused by a GAA repeat expansion within the FXN gene, leading to reduced frataxin levels. This deficiency results in mitochondrial dysregulation, oxidative stress, and progressive cell death. Currently, only one approved treatment exists for FRDA in the United States, Canada, and the European Union, which improves neurological outcomes but has not been fully evaluated for broader disease symptoms. Therefore, identifying new therapeutic targets remains essential. Sphingolipids are increasingly recognized for their roles in neurodegeneration with emerging evidence indicating their dysregulation in FRDA. Here, we investigate whether sphingolipid-metabolizing enzymes are similarly affected and assess the therapeutic potential of targeting them. Our findings demonstrate that these enzymes are dysregulated across multiple FRDA models. Importantly, their modulation in vitro and in vivo significantly reduces mitochondrial dysfunction, enhances frataxin expression, and improves key pathological features of the disease, highlighting sphingolipid metabolism as a promising therapeutic target for FRDA.

Neural crest stem cells (NCSCs) compose a highly migratory, multipotent, stem cell population arising from the neural plate border of the embryonic ectoderm. Investigating the development of NCSCs is critical in understanding both embryonic development and abnormal events that underlie neurocristopathies. Suggested seeding densities in in vitro human induced pluripotent stem cells (hiPSCs) differentiation protocols, varying between 10,000 cells/cm 2 and 200,000 cells/cm 2 , demonstrate a lack of consensus on the optimal conditions to obtain NCSCs. Aiming to maximize the differentiation efficiency of hiPSCs towards the NCSCs lineage, we investigated the effect of the initial seeding density on NCSCs lineage commitment, both in fibroblast- and human peripheral blood mononuclear cell (PBMC)-derived hiPSCs. Cultures were characterized with gene and protein expression analysis assessing stemness ( OCT3/4 and NANOG ), neural crest identity ( SNAI2 and SOX10 ) and neuroectoderm identity ( PAX6 and SOX1 ). We demonstrate that reaching a confluent monolayer of cells by the end of the differentiating protocol is crucial to obtaining NCSCs from hiPSCs. To achieve this, our results indicated 17,000 cells/cm 2 is the optimal initial seeding density. Under this protocol, a confluent monolayer was reached after 8 days of differentiation and an average of 89% SOX10 positive cells were obtained. The fold change of SNAI2 and SOX10 expression was 11-fold and 17-fold higher, respectively, in cultures seeded with 17,000 cells/cm 2 , compared to the highest tested density of 200,000 cells/cm 2 . In contrast, seeding 200,000 cells/cm 2 induced neuroectoderm-like cells, confirmed by an average of 45% of cells marking positive for PAX6. With this work, we demonstrate the importance of achieving cellular confluency during NCSCs differentiation.