Failure to produce mitochondrial DNA results in embryonic lethality in Rnaseh1 null mice

Although ribonucleases H (RNases H) have long been implicated in DNA metabolism, they are not required for viability in prokaryotes or unicellular eukaryotes. We generated Rnaseh1(-/-) mice to investigate the role of RNase H1 in mammals and observed developmental arrest at E8.5 in null embryos. A fraction of the mainly nuclear RNase H1 was targeted to mitochondria, and its absence in embryos resulted in a significant decrease in mitochondrial DNA content, leading to apoptotic cell death. This report links RNase H1 to generation of mitochondrial DNA, providing direct support for the strand-coupled mechanism of mitochondrial DNA replication. These findings also have important implications for therapy of mitochondrial dysfunctions and drug development for the structurally related RNase H of HIV.     

The use of mexamine to reduce radiation injuries during embryogenesis of Wistar rats

In experiments with 330 Wistar rats experiencing their first pregnancy and 1430 neonatal rats of the first generation a study was made on the toxicity and radioprotective efficiency of a single subcutaneous injection of 10 mg/kg mexamine on days 3, 11 and 19 of pregnancy. The agent caused various abnormalities in pregnancy, delivery and postnatal development of the offspring of nonirradiated animals, and it was almost ineffective when used for the prevention of radiation damages during the antenatal ontogenesis.     

Interactions of drugs and radiation in haemopoietic tissue assessed by lethality of mice after whole-body irradiation

Drug-radiation interactions in haemopoietic tissue were assessed as the lethality of mice within 7-28 days after whole-body irradiation. The investigated drugs were adriamycin (ADM), bleomycin (BLM), cyclophosphamide (CTX), 5-fluorouracil (5-FU), methotrexate (MTX), mitomycin C (MM-C) and cis-diamminedichloroplatinum II (cis-DDP). The drugs were administered as single doses 15 min before graded doses of whole-body irradiation or at different intervals from 7 days before to 7 days after fixed radiation doses. ADM, CTX, 5-FU, MM-C and cis-DDP enhanced the radiation response when administered 15 min before irradiation. The dose effect factor (DEF) was 9.11 for 5-FU and in the range 1.25-1.59 for the other drugs. MTX administration 15 min before irradiation had no effect (DEF 1.00). However, MTX increased lethality if given 1-3 days after irradiation (DEF 1.21-1.76) and protected against lethality if given 1-3 days before irradiation (DEF 0.83). A similar time dependence was observed for ADM, CTX, 5-FU, MM-C and cis-DDP. Protection against lethality was not observed but in all these cases the lethality was significantly lower at administration 1-3 days before than 1-3 days after irradiation. A proper investigation of the effect of BLM was not possible as the combination of this drug and whole-body irradiation caused a high rate of gastrointestinal deaths.     

Sensitivity of metallothionein-null mice to LPS/D-galactosamine-induced lethality

Mice treated with lipopolysaccharide (LPS)/D-galactosamine (GalN) selectively develop hepatic failure. The acute-phase protein alpha(1)-acid glycoprotein (AGP) has been demonstrated to protect mice from LPS/GalN-induced lethality. Metallothionein (MT), which is a low-molecular weight, cysteine-rich, metal-binding protein, is also induced in the acute-phase reaction. However, the specific function of MT in acute-phase response remain to be elucidated. We showed that MT-null mice were more sensitive to LPS/GalN-induced lethality than wild-type mice. The increase in vital mediator levels, TNF-alpha and NO were of similar levels in wild-type and MT-null mice. A remarkable increase in plasma platelet-activating factor levels was not observed in our experimental conditions. On the other hands, the mRNA level of AGP in the response to LPS/GalN was decreased in MT-null mice compared to wild-type mice. These results indicated that MT may have the potential to prevent LPS/GalN-induced lethality, at least through the attenuation of AGP induction.     

Disruption of Ini1 leads to peri-implantation lethality and tumorigenesis in mice

SNF5/INI1 is a component of the ATP-dependent chromatin remodeling enzyme family SWI/SNF. Germ line mutations of INI1 have been identified in children with brain and renal rhabdoid tumors, indicating that INI1 is a tumor suppressor. Here we report that disruption of Ini1 expression in mice results in early embryonic lethality. Ini1-null embryos die between 3.5 and 5.5 days postcoitum, and Ini1-null blastocysts fail to hatch, form the trophectoderm, or expand the inner cell mass when cultured in vitro. Furthermore, we report that approximately 15% of Ini1-heterozygous mice present with tumors, mostly undifferentiated or poorly differentiated sarcomas. Tumor formation is associated with a loss of heterozygocity at the Ini1 locus, characterizing Ini1 as a tumor suppressor in mice. Thus, Ini1 is essential for embryo viability and for repression of oncogenesis in the adult organism.     

Japanese encephalitis virus (JEV): potentiation of lethality in mice by microwave radiation.

The expression of Japanese Encephalitis Virus (JEV) lethality in mice requires entry of the virus into the central nervous system. This entry is presumably through the capillary endothelial cells (CEC), because entry between CECs is inhibited by bands of circumferential tight-junctions. A viremic stage occurs during the first 4 to 5 days after JEV administration in mice, and both microwave radiation (2.45-GHz, continuous wave, 10-min exposure) and hypercarbia were employed to increase CEC permeability to JEV. Exposure to microwaves at power densities of 10-50 mW/cm2 resulted in a dose-dependent increase in JEV-induced lethality. Mice did not become tolerant or sensitized to microwave potentiation of JEV-induced mortality because 4 daily exposures at 10 or 50 mW/cm2 (SARS, approximately 24-98 W/kg) did not alter the lethality pattern to subsequent microwave radiation of JEV-exposed animals. Similarly, hypercarbia (5, 10, and 20% CO2) was observed to produce a dose-dependent increase in JEV-induced lethality. Both microwave radiation and hypercarbia are thought to promote pinocytosis in CNS capillary endothelial cells. This may be one mechanism by which they enhance JEV-induced lethality in adult Swiss-Cox mice.     

Strain-specific modification of lethality in fucose-deficient mice

The FX locus encodes an essential enzyme in the de novo pathway of GDP-fucose biosynthesis. Mice homozygous for a targeted mutation of the FX gene manifest a host of pleiotropic abnormalities including a lethal phenotype that is almost completely penetrant in heterozygous intercrosses on a mixed genetic background. Here we have investigated genetic suppression of FX-mediated lethality. Reduced recovery of heterozygous mice was observed while backcrossing the null FX allele to C57BL/6J (B6), but was less dramatic in an outcross to CASA/Rk and absent in an outcross to 129S1/SvImJ, indicating that genetic background modifies survival of FX+/- progeny. Substantial strain-specific differences in pre- and postnatal survival of FX-/- progeny were also detected in heterozygous crosses of C57BL/6J congenic, 129S1B6F1, and B6CASAF1 mice. Specifically, intrauterine survival of FX-/- mice was greatly increased during a heterozygous intercross on a uniform C57BL/6J genetic background compared with survival on a hybrid genetic background consisting of a mixture of C57BL/6J and 129S2/SvPas. In addition, statistically significant clustering of FX-/- progeny into litters and specific breeding cages was noted during a B6CASAF1 FX+/- intercross, suggesting a rare mechanism for modifier gene action in which parentally expressed genes define the phenotype, in this case the survival potential, of mutant offspring. Our results disclose that lethality in FX mutant mice is determined by one or more strain-specific modifier loci.     

Loss of ATM kinase activity leads to embryonic lethality in mice

Ataxia telangiectasia (A-T) mutated (ATM) is a key deoxyribonucleic acid (DNA) damage signaling kinase that regulates DNA repair, cell cycle checkpoints, and apoptosis. The majority of patients with A-T, a cancer-prone neurodegenerative disease, present with null mutations in Atm. To determine whether the functions of ATM are mediated solely by its kinase activity, we generated two mouse models containing single, catalytically inactivating point mutations in Atm. In this paper, we show that, in contrast to Atm-null mice, both D2899A and Q2740P mutations cause early embryonic lethality in mice, without displaying dominant-negative interfering activity. Using conditional deletion, we find that the D2899A mutation in adult mice behaves largely similar to Atm-null cells but shows greater deficiency in homologous recombination (HR) as measured by hypersensitivity to poly (adenosine diphosphate-ribose) polymerase inhibition and increased genomic instability. These results may explain why missense mutations with no detectable kinase activity are rarely found in patients with classical A-T. We propose that ATM kinase-inactive missense mutations, unless otherwise compensated for, interfere with HR during embryogenesis.     

Superoxide dismutase and the oxygen enhancement of radiation lethality

Escherichia coli B were more susceptible to radiation lethality and showed a greater oxygen enhancement ratio when exposed in dilute suspension (1 × 10⁵ cells/ml) than when exposed in dense suspensions (1 × 10⁹ cells/ml). The oxygen enhancement, seen with dilute suspensions, was diminished by superoxide dismutase, catalase, mannitol, or histidine. Heat-denatured superoxide dismutase was without effect. The results are interpreted as indicating a role for O₂^? plus H₂O₂ in the oxygen enhancement of radiation lethality, and a scheme is proposed which is consistent with the observations.     

Analysis of spontaneous early embryonic lethality in mice

The incidence of spontaneously occurring deciduomata is considerably higher in T-stock than in (C3H X C57BL)F1 females. The basis for this difference was studied in vivo, by means of embryo transplantation procedure, and in vitro, by means of short-term embryo culture. Both studies indicate that strain differences in the incidence of spontaneous deciduomata may be largely, if not wholly, accounted for by genetic differences between embryos themselves expressed in terms of the rate of development during the preimplantation period and in the ability to survive the preimplantation and early implantation environment.