Benlefki, S. | bioRxiv Science

bioRxiv2024

Posterior specification of multi-lineage axial assembloids from human pluripotent stem cells.

Elongation of the posterior body axis is driven by multi-potent neuromesodermal progenitors (NMPs), which both self-renew and simultaneously generate neural tube, neural crest, and presomitc mesoderm lineages at successive anterior posterior (A-P) levels. The ensuing diversification of these three NMP lineages is remarkably extensive, and also essential for an immense range of clinically important adult posterior body tissues. Here, we describe a human pluripotent stem cell protocol that successfully specifies authentic NMPs using a cocktail of seven factors (7F). 7F-NMPs express requisite markers, exhibit co-linear HOX activation, and can be purposely specified into each of the three NMP daughter lineages, demonstrating genuine multi-potency. 3D assembly of neural tube, neural crest, and presomitic mesoderm spheroids followed by long-term floating culture derives mature, multi-compartment Posterior Axial Assembloids, or PAXAs. PAXAs constitute a complex heterogeneous tissue containing spinal motor neurons and interneurons, central and peripheral glia, connective tissues, muscle satellite cells and contractile muscle fibres. Together, 7F-NMP and PAXA protocols establish a versatile in vitro platform to model mechanisms of human posterior body axis development, and for the study of a wide range of human diseases.

cell biology↗

bioRxiv2022

Differential effect of Fas activation on spinal muscular atrophy motoneuron death and induction of axonal growth

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) are the most common motoneuron diseases affecting adults and infants, respectively. ALS and SMA are both characterized by the selective degeneration of motoneurons. Although different in their genetic etiology, growing evidence indicate that they share molecular and cellular pathogenic signatures that constitute potential common therapeutic targets. We previously described a motoneuron-specific death pathway elicited by the Fas death receptor, whereby vulnerable ALS motoneurons show an exacerbated sensitivity to Fas activation. However, the mechanisms that drive the loss of SMA motoneurons remains poorly understood. Here, we describe an in vitro model of SMA-associated degeneration using primary motoneurons derived from Smn2B/- SMA mice and show that Fas activation selectively triggers death of the proximal motoneurons. Fas-induced death of SMA motoneurons has the molecular signature of the motoneuron-selective Fas death pathway that requires activation of p38 kinase, caspase-8, -9 and -3 as well as upregulation of collapsin response mediator protein 4 (CRMP4). In addition, Rho Kinase (ROCK) is required for Fas recruitment. Remarkably, we found that exogenous activation of Fas also promotes axonal elongation in both wildtype and SMA motoneurons. Axon outgrowth of motoneurons promoted by Fas requires the activity of ERK, ROCK and caspases. This work defines a dual role of Fas signaling in motoneurons that can elicit distinct responses from cell death to axonal growth.

neuroscience↗