Embryonic Stem Cells License a High Level of Dormant Origins to Protect the Genome against Replication Stress

Abstract

SummaryMaintaining genomic integrity during DNA replication is essential for stem cells. DNA replication origins are licensed by the MCM2–7 complexes, with most of them remaining dormant. Dormant origins (DOs) rescue replication fork stalling in S phase and ensure genome integrity. However, it is not known whether DOs exist and play important roles in any stem cell type. Here, we show that embryonic stem cells (ESCs) contain more DOs than tissue stem/progenitor cells such as neural stem/progenitor cells (NSPCs). Partial depletion of DOs does not affect ESC self-renewal but impairs their differentiation, including toward the neural lineage. However, reduction of DOs in NSPCs impairs their self-renewal due to accumulation of DNA damage and apoptosis. Furthermore, mice with reduced DOs show abnormal neurogenesis and semi-embryonic lethality. Our results reveal that ESCs are equipped with more DOs to better protect against replicative stress than tissue-specific stem/progenitor cells.

Chemotherapy-Induced Depletion of OCT4-Positive Cancer Stem Cells in a Mouse Model of Malignant Testicular Cancer

“…It remains to be seen whether germ cells in fact incur as much DNA damage in response to oncogenic proliferation as do somatic cells, which would also impact DDR activation. Interestingly, ES cells contain greater numbers of dormant origins than more differentiated cells (Ge et al, 2015), and it is conceivable that embryonic germ cells could use this or related mechanisms to protect against replication stress that normally accompanies oncogene-induced hyperproliferation. Whether the DDR is differentially regulated depending on germ cell developmental stage also remains to be determined.…”

Dormant origins as a built-in safeguard in eukaryotic DNA replication against genome instability and disease development

“…In Mcm2 Cre/Cre mice, stem cell numbers are greatly decreased in the sub-ventricular zone of the brain, small intestinal crypt and skeletal muscle with a modest increase of DNA damage relative to wild-type mice [74]. Similarly, neural stem/progenitor cells isolated from Mcm4 c3/c3 embryos show an upsurge of γH2AX and 53BP1 foci with accumulation at the G2/M phases, leading to a reduced ability to form neurospheres when cultured in vitro [125]. Consistently, Mcm4 c3/c3 mice display a defect in embryonic neurogenesis.…”

“…Consistently, Mcm4 c3/c3 mice display a defect in embryonic neurogenesis. In the developing brains of Mcm4 c3/c3 embryos, the renewal of stem cells appears normal, but the number of intermediate progenitor cells is significantly reduced due to an increase of apoptotic cells in the sub-ventricular and intermediate zones [125]. This ultimately stunts ventral forebrain growth and substantially reduces the viability of Mcm4 c3/c3 embryos [125].…”

“…In the developing brains of Mcm4 c3/c3 embryos, the renewal of stem cells appears normal, but the number of intermediate progenitor cells is significantly reduced due to an increase of apoptotic cells in the sub-ventricular and intermediate zones [125]. This ultimately stunts ventral forebrain growth and substantially reduces the viability of Mcm4 c3/c3 embryos [125]. These studies indicate that a full expression of MCM2-7 proteins is needed to support the proper functions of stem/progenitor cells by minimizing replication-associated genome instability.…”

Genome Duplication

“…Even changes in deoxyribonucleotide pools can change the frequency of initiation at minor replication origins (Anglana, Apiou, Bensimon, & Debatisse, 2003). Minor replication origins remain dormant until activated in response to replication stress (Ge et al, 2015; McIntosh & Blow, 2012). Dormant replication origins are licensed origins that become fully active only under conditions that inhibit ongoing DNA replication forks.…”