The NIPBL-gene mutation of a Cornelia de Lange Syndrome patient causes deficits in the hepatocyte differentiation of induced Pluripotent Stem Cells via altered chromatin-accessibility.

Abstract

The Cornelia de Lange syndrome (CdLS) is a rare genetic disease, which is characterized by a cohesinopathy. Mutations of the NIPBL gene are observed in 65% of CdLS patients. A novel iPSC (induced Pluripotent Stem Cell) line was reprogrammed from the leukocytes of a CdLS patient carrying a missense mutation of the NIPBL gene. A mutation-corrected isogenic iPSC-line and two iPSC-lines generated from the healthy parents were used as controls. The iPSC lines were differentiated along the hepatocyte-lineage. Comparative immunofluorescence, RNA-seq and ATAC-seq analyses were performed on undifferentiated and differentiated iPSCs. In addition, chromatin organization was studied by ChIP-Seq analysis on the patient derived iPSCs as well as the respective controls. Relative to the mutation-corrected and the healthy-parents iPSCs, the patient-derived counterparts are defective in terms of differentiation along the hepatocyte-lineage. One-third of the genes selectively up-regulated in CdLS-derived iPSCs and hepatic cells are non-protein-coding genes. By converse, most of the selectively down-regulated genes code for transcription factors and proteins regulating neural differentiation. Some of the transcriptionally silenced loci, such as the DPP6 gene on chromosome 7q36.2 and the ZNF gene cluster on chromosome 19p12, are located in closed-chromatin regions. Relative to the corresponding controls, the global transcriptomic differences observed in CdLS undifferentiated iPSCs are associated with altered chromatin accessibility, which was confirmed by ChIP-Seq analysis. Thus, the deficits in the differentiation along the hepatocyte lineage observed in our CdLS patient is likely to be due to a transcriptional dysregulation resulting from a cohesin-dependent alteration of chromatin accessibility.