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In post-mitotic neurons, aberrant reactivation of cell-cycle signaling precedes degeneration, yet the upstream triggers and functional consequences of this process remain poorly defined. Nucleocytoplasmic transport (NCT) dysfunction, a hallmark of ALS and related disorders, disrupts the spatial distribution of key regulatory proteins and may contribute to maladaptive cell-cycle activation. Our recent evidence suggests that impaired nuclear import may initiate, rather than merely accompany, neuronal cell-cycle re-entry. Here, we show that cell-cycle activation in motor neurons distinguishes molecular subtypes and outcomes in ALS. We analyzed the AnswerALS transcriptomic cohort and identified a patient cluster characterized by robust upregulation of cyclins B and D. Clusters with lower levels of cell-cycle gene expression exhibited accelerated ALSFRS-R decline, whereas the highest cyclin-expressing cluster demonstrated comparatively improved functional trajectories over time. To test whether NCT disruption can mechanistically drive aberrant cell-cycle activation, we pharmacologically inhibited importin-\u03b2 in human iPSC-derived spinal motor neurons. NCT disruption induced widespread proteomic mislocalization, including TDP-43 pathology, and triggered a transient wave of cell-cycle activity preceding neuronal death. Mechanistically, we identified DNA-replication initiation as a pathological event driving degeneration and demonstrated that selective inhibition of G1\/S-associated CDK4\/6 activity confers neuroprotection. Together, these findings link impaired nuclear import to maladaptive cell-cycle reactivation in neurons and highlight stage-specific engagement of the cell-cycle machinery as a determinant of neuronal vulnerability in ALS.<\/jats:p>","DOI":"10.64898\/2026.02.13.705790","type":"posted-content","created":{"date-parts":[[2026,2,16]],"date-time":"2026-02-16T14:30:14Z","timestamp":1771252214000},"source":"Crossref","is-referenced-by-count":1,"title":["Neuronal Cell-Cycle Re-entry Defines Divergent Outcomes Through Replication-Dependent DNA Damage in ALS"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3997-0421","authenticated-orcid":false,"given":"Jonathan","family":"Plessis-Belair","sequence":"first","affiliation":[{"name":"Department of Neurobiology and Behavior; Stony Brook University, Stony Brook, NY 11794, USA"},{"name":"Center for Nervous System Disorders; Stony Brook University, Stony Brook, NY 11794, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3327-537X","authenticated-orcid":false,"given":"Roger B.","family":"Sher","sequence":"additional","affiliation":[{"name":"Department of Neurobiology and Behavior; Stony Brook University, Stony Brook, NY 11794, USA"},{"name":"Center for Nervous System Disorders; Stony Brook University, Stony Brook, NY 11794, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026021814000670000_2026.02.13.705790v1.1","doi-asserted-by":"publisher","DOI":"10.1371\/journal.pbio.3002559"},{"key":"2026021814000670000_2026.02.13.705790v1.2","doi-asserted-by":"publisher","DOI":"10.1523\/JNEUROSCI.23-06-02131.2003"},{"key":"2026021814000670000_2026.02.13.705790v1.3","doi-asserted-by":"publisher","DOI":"10.1016\/S0002-9440(10)63879-5"},{"key":"2026021814000670000_2026.02.13.705790v1.4","doi-asserted-by":"crossref","first-page":"377","DOI":"10.3233\/JAD-2001-3403","article-title":"Hyperphosphorylation of the retinoblastoma gene product and altered subcellular distribution of E2F-1 during Alzheimer\u2019s disease and amyotrophic lateral sclerosis","volume":"3","year":"2001","journal-title":"Journal of Alzheimer\u2019s disease"},{"key":"2026021814000670000_2026.02.13.705790v1.5","doi-asserted-by":"publisher","DOI":"10.1083\/jcb.132.3.413"},{"key":"2026021814000670000_2026.02.13.705790v1.6","doi-asserted-by":"publisher","DOI":"10.1523\/JNEUROSCI.23-07-02557.2003"},{"key":"2026021814000670000_2026.02.13.705790v1.7","doi-asserted-by":"publisher","DOI":"10.1242\/jcs.1125880"},{"key":"2026021814000670000_2026.02.13.705790v1.8","doi-asserted-by":"crossref","first-page":"116444","DOI":"10.1016\/j.biopha.2024.116444","article-title":"\u03b1-synuclein regulates Cyclin D1 to promote abnormal initiation of the cell cycle and induce apoptosis in dopamine neurons","volume":"173","year":"2024","journal-title":"Biomedicine & Pharmacotherapy"},{"key":"2026021814000670000_2026.02.13.705790v1.9","doi-asserted-by":"crossref","first-page":"441","DOI":"10.1038\/s41419-020-2647-1","article-title":"Aberrant activation of neuronal cell cycle caused by dysregulation of ubiquitin ligase Itch results in neurodegeneration","volume":"11","year":"2020","journal-title":"Cell Death & Disease"},{"key":"2026021814000670000_2026.02.13.705790v1.10","doi-asserted-by":"publisher","DOI":"10.1093\/cercor\/bhl164"},{"key":"2026021814000670000_2026.02.13.705790v1.11","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0611671104"},{"key":"2026021814000670000_2026.02.13.705790v1.12","doi-asserted-by":"crossref","first-page":"68","DOI":"10.1093\/jnen\/62.1.68","article-title":"Expression patterns of retinoblastoma protein in Parkinson disease","volume":"62","year":"2003","journal-title":"Journal of Neuropathology & Experimental Neurology"},{"key":"2026021814000670000_2026.02.13.705790v1.13","doi-asserted-by":"crossref","first-page":"757","DOI":"10.1007\/s10571-022-01206-7","article-title":"Deficiency of Parkinson\u2019s related protein DJ-1 alters Cdk5 Signalling and induces neuronal death by aberrant cell cycle re-entry","volume":"43","year":"2023","journal-title":"Cellular and Molecular Neurobiology"},{"key":"2026021814000670000_2026.02.13.705790v1.14","doi-asserted-by":"publisher","DOI":"10.1038\/nrn2124"},{"key":"2026021814000670000_2026.02.13.705790v1.15","doi-asserted-by":"publisher","DOI":"10.2353\/ajpath.2010.090955"},{"key":"2026021814000670000_2026.02.13.705790v1.16","doi-asserted-by":"publisher","DOI":"10.1016\/j.neuron.2017.07.029"},{"key":"2026021814000670000_2026.02.13.705790v1.17","doi-asserted-by":"crossref","first-page":"12175","DOI":"10.3390\/ijms222212175","article-title":"The role of nucleocytoplasmic transport defects in amyotrophic lateral sclerosis","volume":"22","year":"2021","journal-title":"International Journal of Molecular Sciences"},{"key":"2026021814000670000_2026.02.13.705790v1.18","doi-asserted-by":"publisher","DOI":"10.1038\/s41593-017-0047-3"},{"key":"2026021814000670000_2026.02.13.705790v1.19","doi-asserted-by":"publisher","DOI":"10.1080\/19491034.2016.1172152"},{"key":"2026021814000670000_2026.02.13.705790v1.20","first-page":"1","article-title":"Nucleo\u2013cytoplasmic transport defects and protein aggregates in neurodegeneration","volume":"9","year":"2020","journal-title":"Translational Neurodegeneration"},{"key":"2026021814000670000_2026.02.13.705790v1.21","doi-asserted-by":"publisher","DOI":"10.1126\/science.aad9872"},{"key":"2026021814000670000_2026.02.13.705790v1.22","doi-asserted-by":"publisher","DOI":"10.1126\/science.aad2033"},{"key":"2026021814000670000_2026.02.13.705790v1.23","doi-asserted-by":"crossref","unstructured":"J. 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