Initially thought of as primarily a respiratory infection, SARS-CoV-2 is now implicated in substantial central nervous system (CNS) pathology [1][2][3] . CNS symptoms include ischemic strokes, hemorrhages, seizures, encephalopathy, encephalitis/meningitis, anosmia, postinfectious syndromes and neurovasculopathy, collectively described in up to 85% of intensive care unit patients [4][5][6][7] . Several reports appear to meet established criteria for infectious encephalitis 8 . SARS-CoV-2 can utilize angiotensin-converting enzyme 2 (ACE2) as a receptor, although other receptors have been proposed 9,10 . Recent studies on single-cell RNA sequencing (scRNA-seq) datasets indicated low levels of ACE2 expression in brain cells; however, expression is relatively high in some neurovascular unit (NVU) components, particularly in brain pericytes [11][12][13][14] . Autopsy series have suggested the potential for SARS-CoV-2 to spread throughout the brain, especially within vascular and immune cells. They note ischemic brain lesions accompanied by widespread activation of astrocytes and cell death 1,15 . The potential for a SARS-CoV-2 elicited neurovasculopathy supports the development of new models to study tropism and pathology.Brain pericytes are derived from neural crest stem cells (NCSCs) and are uniquely positioned in the NVU, physically linking endothelial and astrocytic cells 16 . Embedded within the basement membrane, pericytes connect, coordinate and regulate signals from neighboring cells to generate responses critical for CNS function in both healthy and disease states, including blood-brain barrier permeability, neuroinflammation, neuronal differentiation and neurogenesis in the adult brain [17][18][19] . Results SARS-CoV-2 productively infects PLCs.We found that green fluorescent protein (GFP) + PLCs generated in vitro from human pluripotent stem cell (hPSC)-derived NCSCs expressed the standard pericyte markers NG2 and PDGFR-β (Fig. 1a,b) 20 . We detected appreciable ACE2 messenger RNA and protein in PLCs cultured two-dimensionally compared with cultured human neural precursors (Extended Data Fig. 1a-d) 14,21 . To assess SARS-CoV-2 PLC tropism, we exposed PLCs to authentic SARS-CoV-2 at a multiplicity of infection (MOI) of 0.5, then collected the supernatant and cells daily (Fig. 1c). We found that the percentage of SARS-CoV-2 nucleocapsid protein + cells and viral RNA as measured by quantitative PCR with reverse transcription (RT-qPCR) increased daily up to 72 h postinfection, from 0 to 65% SARS-CoV-2 nucleocapsid protein + , with viral RNA load increasing up to approximately 1,000-fold (Fig. 1d,e). Plaque assay from the PLC supernatants on Vero E6 cells showed approximately 100-fold increased infectious virus production at 24 h postinfection with increased viral RNA as well as viral titers compared to baseline, suggesting viral production by PLCs (Fig. 1f-h) 22 . Furthermore, we found that ACE2 receptor-blocking antibody partially prevented SARS-CoV-2 infection of PLCs (Extended Data Fig. 2a-e) 23 .PCCO generat...
Asparaginyl-tRNA synthetase1 (NARS1) is a member of the ubiquitously expressed cytoplasmic Class IIa family of tRNA synthetases required for protein translation. Here, we identify biallelic missense and frameshift mutations in NARS1 in seven patients from three unrelated families with microcephaly and neurodevelopmental delay. Patient cells show reduced NARS1 protein, impaired NARS1 activity and impaired global protein synthesis. Cortical brain organoid modeling shows reduced proliferation of radial glial cells (RGCs), leading to smaller organoids characteristic of microcephaly. Single-cell analysis reveals altered constituents of both astrocytic and RGC lineages, suggesting a requirement for NARS1 in RGC proliferation. Our findings demonstrate that NARS1 is required to meet protein synthetic needs and to support RGC proliferation in human brain development.
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