Early embryonic lethality in PARP-1 Atm double-mutant mice suggests a functional synergy in cell proliferation during development

Abstract

PARP-1 and ATM are both involved in the response to DNA strand breaks, resulting in induction of a signaling network responsible for DNA surveillance, cellular recovery, and cell survival. ATM interacts with double-strand break repair pathways and induces signals resulting in the control of the cell cycle-coupled checkpoints. PARP-1 acts as a DNA break sensor in the base excision repair pathway of DNA. Mice with mutations inactivating either protein show radiosensitivity and high radiation-induced chromosomal aberration frequencies. Embryos carrying double mutations of both PARP-1 and Atm genes were generated. These mutant embryos show apoptosis in the embryo but not in extraembryonic tissues and die at embryonic day 8.0, although extraembryonic tissues appear normal for up to 10.5 days of gestation. These results reveal a functional synergy between PARP-1 and ATM during a period of embryogenesis when cell cycle checkpoints are not active and the embryo is particularly sensitive to DNA damage. These results suggest that ATM and PARP-1 have synergistic phenotypes due to the effects of these proteins on signaling DNA damage and/or on distinct pathways of DNA repair.

FIG. 1

External views and histological sections of E8.0 and E9.5 normal (N, not genotyped; PARP-1^−/− Atm^+/− [−/−;+/−]) and PARP-1 Atm double-null (−/−;−/−) conceptuses. The embryo in panel c was taken out of its yolk sac. Abbreviations: A, amnion; AC, amniotic cavity; AL, allantois; EC, ectoplacental cavity; EM, embryo; F, foregut pocket; H, head folds; P, placenta; S, somites; Y, yolk sac; YC, yolk sac cavity. Small arrows, condensed nuclear fragments. The same magnifications were used for panels a and b and for panels c and d. Scale bar (bar in panel h applies to panels e to h): 250 μm (e and f) and 25 μm (g and h).

FIG. 2

Histological and electron-microscopic analysis of E10.5 and E11.5 normal mice (N) and presumptive PARP-1 Atm double-null mutants (−/−;−/−). Panels b and d represent high magnifications of areas similar to those designated in panel a by EM and Y, respectively. The inset in panel e is a low-magnification view of the embryo and yolk sac displayed in panels e and f. (b and d) Abnormal E10.5 embryos; (e to h) abnormal E11.5 embryos. Abbreviations: B, primitive blood islands; EM, embryo; M, maternal blood sinus; P, placenta; T, trophoblast cell; V, visceral endoderm; Y, visceral portion of the yolk sac; YC, yolk sac cavity. Arrows, condensed nuclear fragments; double arrow, phagocytosis of one of these fragments by an embryonic cell. Scale bar (bar in panel h applies to all panels): 280 μm (a), 15 μm (b), 20 μm (c and d to g), and 3 μm (h).

FIG. 3

Signal transduction pathways leading to DNA repair and checkpoint induction by PARP-1 and Atm. PARP-1 is activated by breaks in DNA and is likely to recruit XRCC1 and the BER complex on the site of the lesion, allowing efficient DNA repair and cell cycle progression. ATM, a DNA double-stranded break enzyme, phosphorylates p53 specifically to selectively induce G₁ arrest via p21 transcription.