Alteration of Genomic Imprinting Status of Human Parthenogenetic Induced Pluripotent Stem Cells during Neural Lineage Differentiation

Selection of iPSCs without mtDNA deletion for autologous cell therapy in a patient with Pearson syndrome

Screening for genetic defects in the cells should be examined for clinical application. The Pearson syndrome (PS) patient harbored nuclear mutations in the POLG and SSBP1 genes, which could induce systemic large-scale mitochondrial genome (mtDNA) deletion. We investigated iPSCs with mtDNA deletions in PS patient and whether deletion levels could be maintained during differentiation. The iPSC clones derived from skin fibroblasts (9% deletion) and blood mononuclear cells (24% deletion) were measured for mtDNA deletion levels. Of the 13 skin-derived iPSC clones, only 3 were found to be free of mtDNA deletions, whereas all blood-derived iPSC clones were found to be free of deletions. The iPSC clones with (27%) and without mtDNA deletion (0%) were selected and performed in vitro and in vivo differentiation, such as embryonic body (EB) and teratoma formation. After differentiation, the level of deletion was retained or increased in EBs (24%) or teratoma (45%) from deletion iPSC clone, while, the absence of deletions showed in all EBs and teratomas from deletion-free iPSC clones. These results demonstrated that non-deletion in iPSCs was maintained during in vitro and in vivo differentiation, even in the presence of nuclear mutations, suggesting that deletion-free iPSC clones could be candidates for autologous cell therapy in patients. [BMB Reports 2023; 56(8): 463-468].

Abnormal DNA methylation in pluripotent stem cells from a patient with Prader-Willi syndrome results in neuronal differentiation defects

DNA methylation is a common method of gene expression regulation, and this form of regulation occurs in the neurodevelopmental disorder Prader-Willi syndrome (PWS). Gene expression regulation via methylation is important for humans, although there is little understanding of the role of methylation in neuronal differentiation. We characterized the cellular differentiation potential of iPS cells derived from a patient with PWS with abnormal methylation (M-iPWS cells). A comparative genomic hybridization (CGH) array revealed that, unlike iPWS cells (deletion genes type), the abnormally methylated M-iPWS cells had no deletion in the15q11.2-q13 chromosome region. In addition, methylation-specific PCR showed that M-iPWS cells had strong methylation in CpG island of the small nuclear ribonucleoprotein polypeptide N (SNRPN) on both alleles. To assess the effect of abnormal methylation on cell differentiation, the M-iPWS and iPWS cells were induced to differentiate into embryoid bodies (EBs). The results suggest that iPWS and M-iPWS cells are defective at differentiation into ectoderm. Neural stem cells (NSCs) and neurons derived from M-iPWS cells had fewer NSCs and mature neurons with low expression of NSCs and neuronal markers. We conclude that expression of the downstream of genes in the PWS region regulated by methylation is involved in neuronal differentiation.

Generation of human androgenetic induced pluripotent stem cells

In humans, parthenogenesis and androgenesis occur naturally in mature cystic ovarian teratomas and androgenetic complete hydatidiform moles (CHM), respectively. Our previous study has reported human parthenogenetic induced pluripotent stem cells from ovarian teratoma-derived fibroblasts and screening of imprinted genes using genome-wide DNA methylation analysis. However, due to the lack of the counterparts of uniparental cells, identification of new imprinted differentially methylated regions has been limited. CHM are inherited from only the paternal genome. In this study, we generated human androgenetic induced pluripotent stem cells (AgHiPSCs) from primary androgenetic fibroblasts derived from CHM. To investigate the pluripotency state of AgHiPSCs, we analyzed their cellular and molecular characteristics. We tested the DNA methylation status of imprinted genes using bisulfite sequencing and demonstrated the androgenetic identity of AgHiPSCs. AgHiPSCs might be an attractive alternative source of human androgenetic embryonic stem cells. Furthermore, AgHiPSCs can be used in regenerative medicine, for analysis of genomic imprinting, to study imprinting-related development, and for disease modeling in humans.

Genome imprinting in stem cells: A mini-review

Genomic imprinting is an epigenetic process result in silencing of one of the two alleles (maternal or paternal) based on the parent of origin. Dysregulation of imprinted genes results in detectable developmental and differential abnormalities. Epigenetics erasure is required for resetting the cell identity to a ground state during the production of induced pluripotent stem (iPS) cells from somatic cells. There are some contradictory reports regarding the status of the imprinting marks in the genome of iPS cells. Additionally, many studies highlighted the existence of subtle differences in the imprinting loci between different types of iPS cells and embryonic stem (ES) cells. These observations could ultimately undermine the use of patient-derived iPS cells for regenerative medicine.