Repetitive Sequence Stability in Embryonic Stem Cells

Repetitive sequences play an indispensable role in gene expression, transcriptional regulation, and chromosome arrangements through trans and cis regulation. In this review, focusing on recent advances, we summarize the epigenetic regulatory mechanisms of repetitive sequences in embryonic stem cells. We aim to bridge the knowledge gap by discussing DNA damage repair pathway choices on repetitive sequences and summarizing the significance of chromatin organization on repetitive sequences in response to DNA damage. By consolidating these insights, we underscore the critical relationship between the stability of repetitive sequences and early embryonic development, seeking to provide a deeper understanding of repetitive sequence stability and setting the stage for further research and potential therapeutic strategies in developmental biology and regenerative medicine.

Specialized Circuitry of Embryonic Stem Cells Promotes Genomic Integrity

Embryonic stem cells (ESCs) give rise to all cell types of the organism. Given the importance of these cells in this process, ESCs must employ robust mechanisms to protect genomic integrity or risk catastrophic propagation of mutations throughout the organism. Should such an event occur in daughter cells that will eventually contribute to the germline, the overall species health could dramatically decline. This review describes several key mechanisms employed by ESCs that are unique to these cells, in order to maintain their genomic integrity. Additionally, the contributions of cell cycle regulators in modulating ESC differentiation, after DNA damage exposure, are also examined. Where data are available, findings reported in ESCs are extended to include observations described in induced pluripotent stem cells (IPSCs).

Human neural stem cells drug product: Microsatellite instability analysis

Introduction

In central nervous system neurodegenerative disorders, stem cell-based therapies should be considered as a promising therapeutic approach. The safe use of human Neural Stem Cells (hNSCs) for the treatment of several neurological diseases is currently under evaluation of phase I/II clinical trials. Clinical application of hNSCs require the development of GMP standardized protocols capable of generating high quantities of reproducible and well characterized stem cells bearing stable functional and genetic properties.

Aim

The aim of this study was to evaluate possible instabilities or modifications of the microsatellite loci in different culture passages because high culture passages represent an in vitro replicative stress leading to senescence.

Experimental method: The hNSCs were characterized at different culture time points, from passage 2 to passage 25, by genetic typing at ten microsatellite loci.

Conclusion

We showed that genetic stability at microsatellite loci is maintained by the cells even at high passages adding a further demonstration of the safety of our hNSCs GMP culture method.

Insertion/deletion and microsatellite alteration profiles in induced pluripotent stem cells

We here demonstrate that microsatellite (MS) alterations are elevated in both mouse and human induced pluripotent stem cells (iPSCs), but importantly we have now identified a type of human iPSC in which these alterations are considerably reduced. We aimed in our present analyses to profile the InDels in iPSC/ntESC genomes, especially in MS regions. To detect somatic de novo mutations in particular, we generated 13 independent reprogramed stem cell lines (11 iPSC and 2 ntESC lines) from an identical parent somatic cell fraction of a C57BL/6 mouse. By using this cell set with an identical genetic background, we could comprehensively detect clone-specific alterations and, importantly, experimentally validate them. The effectiveness of employing sister clones for detecting somatic de novo mutations was thereby demonstrated. We then successfully applied this approach to human iPSCs. Our results require further careful genomic analysis but make an important inroad into solving the issue of genome abnormalities in iPSCs.

High frequency of microsatellite instability and its substantial co-existence with KRAS and BRAF mutations in Vietnamese patients with colorectal cancer

Tumor heterogeneity and resistance to chemotherapy have been recognized as two major obstacles in the diagnosis and treatment of colorectal cancer (CRC). Microsatellite instability (MSI) and KRAS and BRAF mutations are common diagnostic factors that have been widely used to classify CRC for therapeutics. In the present study, 151 patients with CRC were analyzed from the two most populous ethnic groups of Vietnam, Kinh and Muong, for their MSI status, frequency of KRAS and BRAF mutations, and their clinical implications. MSI-high (MSI-H) was detected in 45.0% (68/151), while mutated KRAS and BRAF were identified in 37.1% (56/151) and 2.6% (4/151) of the cases, respectively. There was a substantial co-existence of MSI-H with KRAS (27/56; 48.2%) and BRAF (3/4; 75.0%) mutations. Statistical analysis showed that MSI-H tumors were significantly associated with colon location (P=0.011) and more advanced T stages (P=0.016). KRAS exon 2 mutations were significantly more likely to be detected in patients who belonged to the Muong ethnic group (P=0.013) or those with no/fewer lymph node metastasis (P=0.048) as compared with their counterparts. In summary, the data revealed typical molecular features of Vietnamese patients with CRC, including a strikingly high rate of MSI-H and its high co-existence with KRAS and BRAF mutations, which should be carefully considered in the future therapeutics for this type of cancer.

DNA repair fidelity in stem cell maintenance, health, and disease

Stem cells are a sub population of cell types that form the foundation of our body, and have the potential to replicate, replenish and repair limitlessly to maintain the tissue and organ homeostasis. Increased lifetime and frequent replication set them vulnerable for both exogenous and endogenous agents-induced DNA damage compared to normal cells. To counter these damages and preserve genetic information, stem cells have evolved with various DNA damage response and repair mechanisms. Furthermore, upon experiencing irreparable DNA damage, stem cells mostly prefer early senescence or apoptosis to avoid the accumulation of damages. However, the failure of these mechanisms leads to various diseases, including cancer. Especially, given the importance of stem cells in early development, DNA repair deficiency in stem cells leads to various disabilities like developmental delay, premature aging, sensitivity to DNA damaging agents, degenerative diseases, etc. In this review, we have summarized the recent update about how DNA repair mechanisms are regulated in stem cells and their association with disease progression and pathogenesis.