Targeted disruption of the cell-cycle checkpoint gene ATR leads to early embryonic lethality in mice

Abstract

Checkpoints of DNA integrity are conserved throughout evolution, as are the kinases ATM (Ataxia Telangiectasia mutated) and ATR (Ataxia- and Rad-related), which are related to phosphatidylinositol (PI) 3-kinase [1] [2] [3]. The ATM gene is not essential, but mutations lead to ataxia telangiectasia (AT), a pleiotropic disorder characterised by radiation sensitivity and cellular checkpoint defects in response to ionising radiation [4] [5] [6]. The ATR gene has not been associated with human syndromes and, structurally, is more closely related to the canonical yeast checkpoint genes rad3(Sp) and MEC1(Sc) [7] [8]. ATR has been implicated in the response to ultraviolet (UV) radiation and blocks to DNA synthesis [8] [9] [10] [11], and may phosphorylate p53 [12] [13], suggesting that ATM and ATR may have similar and, perhaps, complementary roles in cell-cycle control after DNA damage. Here, we report that targeted inactivation of ATR in mice by disruption of the kinase domain leads to early embryonic lethality before embryonic day 8.5 (E8.5). Heterozygous mice were fertile and had no aberrant phenotype, despite a lower ATR mRNA level. No increase was observed in the sensitivity of ATR(+/-) embryonic stem (ES) cells to a variety of DNA-damaging agents. Attempts to target the remaining wild-type ATR allele in heterozygous ATR(+/-) ES cells failed, supporting the idea that loss of both alleles of the ATR gene, even at the ES-cell level, is lethal. Thus, in contrast to the closely related checkpoint gene ATM, ATR has an essential function in early mammalian development.

Harnessing the complexity of DNA-damage response pathways to improve cancer treatment outcomes

“…However, they appear to have independent functions in the progression through a normal, unperturbed, cell cycle. Consistent with this, ATR deficiency in mice results in early embryonic lethality associated with the loss of cellular proliferative potential and extensive apoptosis, whereas cells and animals survive quite well without ATM (Barlow et al, 1998;Brown and Baltimore, 2000;de Klein et al, 2000).…”

Inhibition of the ATR/Chk1 Pathway Induces a p38-Dependent S-phase Delay in Mouse ES Cells

“…Our observations of the effects of caffeine in ES cells are consistent with recent findings indicating the importance of ATR-Chk1 signaling pathway during normal cell cycle in both somatic and embryonic cells. 23,54 Both ATR -/-and Chk1 -/-mouse embryos die between E3.5 (blastocysts stage) and E7.5 due to the chromosomal fragmentation, chromatin aggregation and consequent caspase-mediated apoptosis. 24,25,55 It is been published by Nghiem et al 30 that ATR kinase activity is critical especially during S phase and that S-phase arrested cells are susceptible to premature chromatin condensation (PCC) and chromosome breaks following ATR suppression.…”

“…ATR -/-mouse embryos develop to the blastocyst stage but die between E3.5 and E7.5 due to chromosome aberrations and caspase-dependent apoptosis. [23][24][25] Effects similar to that in ATR -/-were observed in Chk1 -/-mouse embryos and Chk1 -/-ES cells. 26 Chk1 and Chk2 kinases are downstream of ATM and ATR and they are also involved in DNA damage checkpoints.…”

Understanding the molecular basis of common fragile sites instability: Role of the proteins involved in the recovery of stalled replication forks

“…Unlike ATM, deletion of ATR in mice results in an embryonic lethal phenotype indicating that ATR is an essential gene. 26,27 ATR disruption or hypomorphic mutation in ATR greatly increases chromosome instability and gives rise to breakage at CFS following low dose of aphidicolin. 16,28 Interestingly, ATR deficiency alone results in CFS expression without the addition of replication inhibitors, 16 indicating that replication fork stalling may occur spontaneously at these regions.…”