Modeling ATN1 mutations in human iPSCs reveals early developmental roles of atrophin-1

Atrophin-1 (ATN1), encoded by the ATN1 gene, is an evolutionarily conserved transcriptional corepressor implicated in neuronal development and severe incurable disorders, including the polyglutamine (polyQ) disease - dentatorubral-pallidoluysian atrophy (DRPLA), and the neurodevelopmental syndrome CHEDDA. However, the cellular function of ATN1 and its role during early human development remain largely uncharacterized. Here, we generated an isogenic panel of human induced pluripotent stem cell (iPSC) lines, establishing a novel resource for comprehensive studies of ATN1 function and dysfunction. This panel includes a DRPLA patient-derived line (wt/mut), CRISPR-Cas9-corrected wild-type controls (wt/wt), complete ATN1 knock-out clones (-/-), and heterozygous lines expressing either a wild-type or a mutant allele (wt/- and -/mut). While pluripotency markers remained unaffected across all variants, further characterization revealed marked proliferation deficits in ATN1 knock-out lines and heterozygous iPSCs without wild-type allele expression. Moreover, the formation of punctate ATN1 assemblies was enhanced in iPSCs with -/mut variants. The pronounced phenotype observed in cells expressing only the mutant ATN1 allele may result from a combination of loss-of-function and toxic gain-of-function mechanisms. Overall, the generated panel of iPSC lines provides a unique cellular platform for investigating ATN1-dependent molecular mechanisms and their contribution to neuronal development and disease.