C9orf72 poly-GA proteins impair neuromuscular transmission

Amyotrophic lateral sclerosis(ALS) is a devastating motoneuron disease,in which lower motoneurons lose control of skeletal muscles.Degeneration of neuromuscular junctions(NMJs) occurs at the initial stage of ALS.Dipeptide repeat proteins(DPRs) from G4C2repeat-associated non-ATG(RAN) translation are known to cause C9orf72-associated ALS(C9-ALS).However,DPR inclusion burdens are weakly correlated with neurodegenerative areas in C9-ALS patients,indicating that DPRs may exert cell non-autonomous effects,in addition to the known intracellular pathological mechanisms.Here,we report that poly-GA,the most abundant form of DPR in C9-ALS,is released from cells.Local administration of poly-GA proteins in peripheral synaptic regions causes muscle weakness and impaired neuromuscular transmission in vivo.The NMJ structure cannot be maintained,as evidenced by the fragmentation of postsynaptic acetylcholine receptor(AChR) clusters and distortion of presynaptic nerve terminals.Mechanistic study demonstrated that extracellular poly-GA sequesters soluble Agrin ligands and inhibits Agrin-MuSK signaling.Our findings provide a novel cell non-autonomous mechanism by which poly-GA impairs NMJs in C9-ALS.Thus,targeting NMJs could be an early therapeutic intervention for C9-ALS.

Dual-specificity histone demethylase KIAA1718 （KDM7A） regulates neural differentiation through FGF4

Dimethylations of histone H3 lysine 9 and lysine 27 are important epigenetic marks associated with transcription repression. Here, we identified KIAA1718 （KDM7A） as a novel histone demethylase specific for these two repressing marks. Using mouse embryonic stem cells, we demonstrated that KIAA1718 expression increased at the early phase of neural differentiation. Knockdown of the gene blocked neural differentiation and the effect was rescued by the wild-type human gene, and not by a catalytically inactive mutant. In addition, overexpression of KIAA1718 accelerated neural differentiation. We provide the evidence that the pro-neural differentiation effect of KDM7A is mediated through direct transcriptional activation of FGF4, a signal molecule implicated in neural differentiation. Thus, our study identified a dual-specificity histone demethylase that regulates neural differentiation through FGF4.

Direct conversion of human fibroblasts into retinal pigment epithelium-like cells by defined factors

The generation of functional retinal pigment epithelium （RPE） is of great therapeutic interest to the field of regenerative medicine and may provide possible cures for retinal degenerative diseases, including age-related macular degeneration （AMD）. Although RPE cells can be produced from either embryonic stem cells or induced pluripotent stem cells, direct cell reprogramming driven by lineage-determining transcription factors provides an immediate route to their generation. By monitoring a human RPE specific Bestl：：GFP reporter, we report the conversion of human fibroblasts into RPE lineage using defined sets of transcription factors. We found that Bestl：：GFP positive cells formed colonies and exhibited morphological and molecular features of early stage RPE cells. Moreover, they were able to obtain pigmen- tation upon activation of Retinoic acid （RA） and Sonic Hedgehog （SHH） signaling pathways. Our study not only established an ideal platform to investigate the tran- scriptional network regulating the RPE cell fate deter- mination, but also provided an alternative strategy to generate functional RPE cells that complement the useof pluripotent stem cells for disease modeling, drug screening, and cell therapy of retinal degeneration.

Human neuromuscular junction three-dimensional organoid models and the insight in motor disorders

The neuromuscular junction(NMJ),a peripheral synaptic connection between motoneurons and skeletal muscle fibers,controls movement.Dysregulation of NMJs has been implicated in various motor disorders.Because of their large size and easy accessibility,NMJs have been extensively investigated in the neuroscience field and have greatly contributed to our understanding of the fundamental principles of synapses in the central nervous system.Researchers have tried multiple ways to develop models to recreate NMJs.Rapid progress in the research and development of tissue-like organoids has made it possible to produce human NMJ three-dimensional(3D)models in vitro,providing an additional powerful strategy to study NMJs.Here,we introduce the most recent advances of human embryonic stem cell-or induced pluripotent stem cell-derived organoids to model 3D NMJs.