Chromosomal Instability and Molecular Defects in Induced Pluripotent Stem Cells from Nijmegen Breakage Syndrome Patients

Abstract

Nijmegen breakage syndrome (NBS) results from theabsence of the NBS1 protein, responsible for detection of DNA double-strand breaks (DSBs). NBS is characterized by microcephaly, growth retardation, immunodeficiency, and cancer predisposition. Here, we show successful reprogramming ofNBS fibroblasts into induced pluripotent stem cells (NBS-iPSCs). Our data suggest a strong selection for karyotypically normal fibroblasts to go throughthe reprogramming process. NBS-iPSCs then acquire numerous chromosomal aberrations and show a delayed response to DSB induction. Furthermore, NBS-iPSCs display slower growth, mitotic inhibition, a reduced apoptotic response tostress, and abnormal cell-cycle-related gene expression. Importantly, NBS neural progenitor cells (NBS-NPCs) show downregulation of neural developmental genes, which seems to be mediated by P53. Our results demonstrate the importance of NBS1 in early human development, shed light on the molecular mechanisms underlying this severe syndrome, and further expand our knowledge of the genomic stress cells experience during the reprogramming process.