Post-implantation Lethality Research Articles

Targeted disruption of the even-skipped gene, evx1, causes early postimplantation lethality of the mouse conceptus.

Implantation within the mammalian uterus elicits dramatic changes in the growth, differentiation, and morphogenesis of the conceptus. This process is interrupted in mice carrying a targeted disruption of the murine evx1 gene, a homolog of the Drosophila even-skipped (eve) gene. Upon implantation, presumptive evx1- homozygotes elicit a decidual response, invade the uterine epithelium, and attach to the basement membrane between uterine stroma and epithelium, but fail to differentiate extraembryonic tissues or to form egg cylinders prior to resorption. Retrograde analysis of embryo genotypes demonstrates that homozygotes could be isolated as free-floating blastocysts but not as gastrulating egg cylinders. Homozygous mutant blastocysts appeared normal and, when grown in vitro, attach, proliferate, and form trophoblastic giant cells surrounding a growing inner cell mass before rapidly degenerating. In situ hybridization analysis demonstrates evx1 gene expression within the visceral endoderm after implantation and prior to gastrulation, at a time in which the mutant phenotype is first detected.

The influence of mating status and age on the induction of chromosome aberrations and dominant lethals in irradiated female mice

Young and old hybrid female mice were given 0.5 Gy or 2 Gy acute x-irradiation, followed by (i) in utero examination for dominant lethal mutations, or (ii) examination of metaphase I oocytes for chromosome aberrations 2–3 weeks after the irradiation. Some of the old females had been mated when young to males of a specific locus stock. Others were left unmated until after the irradiation when they, and the young females, were mated to the same specific locus stock and allowed to have 1 (if given 2 Gy) or 2 (if given 0.5 Gy) litters before the dominant lethal test. In both the 0.5 -Gy and 2-Gy series, mean sizes of first litters in the old late-mated group were markedly lower than in the old early-mated or young groups, the differences being significant at the 2-Gy level. The intrauterine examinations showed that this difference was largely the result of a reduced ovulation rate in the old late-mated females. Preimplantation loss tended to be higher in all the old females than in the young ones, but differences between the groups in postimplantation lethality were less pronounced. In the chromosome studies, only about half as many oocytes were recovered from the ovaries of old females than from young ones. At both the 0.5-Gy and 2-Gy dose levels interchange frequencies were non-significantly higher in old than in young females (with no clear-cut effect of mating status), while the overall frequency of aberrations (interchanges + fragments) was significantly higher in oocytes of old than young females after 2 Gy X-rays (35.5% against 12.5%). No specific locus mutations were found in 5616 offspring of unirradiated females.

Mutagenic efficiency of organophosphorus insecticides used in combined treatments.

Male mice (Q strain) received two consecutive injections of organophosphorus insecticides: a phosphonate (trichlorfon) was combined to a thiophosphate (methylparathion) or a dithiophosphate (malathion or methylazinphos) in order to evaluate the interactions at the genetic and cytogenetic levels. No increase in chromosome damage was observed in bone marrow cells, spermatogonia, and primary spermatocytes. In a dominant lethal mutation assay, the frequency of postimplantation lethality was not significantly increased over the control level. The percentage of preimplantation losses was enhanced, probably due to a toxic effect on male germ cells.

Dominant lethal and ovarian effects of plutonium-239 in female mice.

In two separate experiments (C3H x 101)F1 female mice were injected intravenously with 239Pu in trisodium citrate, then mated in pairs to strain CBA males, to test for dominant lethality. In the first experiment 10 muCi kg-1 and in the second 20 muCi kg-1 body mass was injected. Matings were after 6 days in the first experiment (estimated ovarian absorbed dose of 0.1 Gy) and after 3, 6 or 12 weeks in the second (estimated ovarian doses of 1.11, 2.45 and 5.91 Gy respectively). No evidence of dominant lethal induction was found in the first experiment, but in the second there was a significant increase over controls in pre-implantation loss in all three series. Post-implantation lethality increased significantly (by 12 per cent) only after 12 weeks' exposure. With the 6- and 12-week exposures (especially the latter) luteal counts fell and fewer females became pregnant than in controls. This is attributed to oocyte killing by the alpha-particles. Histological and autoradiographic investigations showed a marked reduction in ovarian size and follicular numbers with fission-tracks clustered mainly over the medullary stroma. The pre-implantation loss may stem from lowered fertilization of oocytes because of their damage, so that the best measure of dominant lethality is that based on post-implantation death. Thus there is only slight evidence for the induction of genetic damage, which is in line with previous findings after chronic exposures of female mice.

Dominant lethal mutations in male mice fed γ-irradiated diet

Three groups of Swiss male mice were fed a stock ration or an unirradiated or irradiated (2·5 Mrad) test diet for 8 wk. After the feeding period, the males were mated with groups of untreated female mice for 4 consecutive weeks. The females were autopsied at mid-term pregnancy for evaluation of dominant lethal mutations. Numbers of dead implantations, including deciduomas and dead embryos, showed no significant differences among the different groups, thus producing no evidence of any induced post-implantation lethality in mice fed on irradiated diet. Similarly, there was no indication of pre-implantation lethality, since implantation rates remained comparable among different groups. Consumption of irradiated diet did not affect the fertility of mice. Total pre- and post-implantation loss, as indicated by the numbers of live implantations remained comparable among all the groups of mice.

Cytogenetic effects of X-rays and fission neutrons in female mice

The induction by X-rays of chromosomal damage in oocytes was studied, while the genetic consequences of X- and neutron-induced damage in female mice were looked for by testing offspring for dominant lethality and semi-sterility. None out of 386 sons of hybrid females given 300 rad X-rays showed evidence of semi-sterility or translocation heterozygosity, but 9 out of 294 daughters were diagnosed as semi-sterile. At least 3 and probably 4 of these (1.4%) carried reciprocal translocations, 2 of which caused male sterility. Complete or partial loss of the X-chromosome may have been responsible for some of the other sermi-steriles. Examination of oocytes at metaphase-I during the first and third weeks after X-irradiation with 100 or 400 rad revealed both multivalents (some of the ring quadrivalent type) and fragments (mainly double). These were thought to arise mainly from chromatid intercchanges (both symmetrical and asymmetrical) and isochromatid intrachanges respectively. Since neither the proportion of asymmetrical interchanges nor the amount of hidden damage was known it was not thought possible to predict the magnitude of F 1 effects from metaphase-I findings. The aberration frequency in oocytes rose with dose and (at the 400 rad level only) with time after irradiation, reaching a maximum of 10% multivalents and 22% fragments in the third week after 400 rad. The frequency of univalents showed no consistent trend, but chiasma counts decreased in the first week after 400 rad. The increase in levels of chromosomal damage with dose and time after irradiation was reflected in dominant lethal frequencies after the same radiation-conception intervals and doses of 0–400 rad. Induced post-implantation lethality was over twice as high in the third week after 200–400 rad than in the first. Pre-implantation loss also greatly increased in the third week after 300 or 400 rad; this was associated with increased non-fertilization of ova. No evidence for the induction of translocations in oogonia or resting oocytes by fast neutron irradiation was obtained, although there was evidence for X-chromosomal loss after 200 rad to oocytes. The relative biological effectiveness (RBE) for fission neutrons vs. X-rays with respect to dominant lethal induction in oocytes was found to vary with dose, but seamed to be around 1 at lower levels.