The development potential of ethanol-induced monosomic and trisomic conceptuses in the mouse

Embryo developmental disruption during organogenesis produced by CF-1 murine periconceptional alcohol consumption

The aim was to study the control females (CF)-1 mouse embryo differentiation, growth, morphology on embryonic E- and N-cadherin expression at midgestation after periconceptional moderate alcohol ingestion. Adult female mice were exposed to 10% ethanol in drinking water for 17 days previous to and up to day 10 of gestation (ethanol-exposed females, EF) and were compared with nonexposed CF. EF presented reduced quantities of E10 to E10.5 embryos, greater percentage of embryos at stages less than E7.5, reduced implantation site numbers/female, and increased resorptions compared with CF. EF-embryo growth was significantly affected as evidenced by reduced cephalic and body sizes of E10 and E10.5 embryos (scanning electron microscopy) and decreased protein content of E10.5 embryos vs. CF embryos. A significantly higher percentage of EF-E10-10.5 embryos presented abnormal neural tube (NT) closure vs. the percentage of CF. E10 embryos from EF presented elevated tissue disorganization, pyknosis and nuclear condensation in somites, mesenchymal and neuroepithelial tissue. Immunohistochemical E- and N-cadherin distribution patterns were similar in organic structures of E10 embryos between groups. However, western blot revealed that E- and N-cadherin expression levels were significantly increased in EF-derived embryos vs. controls. Perigestational ethanol consumption by CF-1 mice induced significant damage in the organogenic embryogenesis by producing delayed differentiation, growth deficiencies, and increasing the frequency of NT defects. Ethanol exposure may disrupt cell-cell adhesion leading to upregulation of E- and N-cadherin expression suggesting that deregulation of cell adhesion molecules could be involved in the disruption of embryo development at organogenesis in CF-1 mouse.

Important biological variables that can influence the degree of chemical-induced aneuploidy in mammalian oocyte and zygotes

The ability of certain chemicals to increase the frequency of aneuploidy in mammalian oocytes elicits concern about human health and well-being. This concernment exists because aneuploidy is the most prevalent class of human genetic disorders, and very little information exists about the etiology of aneuploidy. Although there are experimental models for studying aneuploidy in female germ cells and zygotes, these models are still being validated because insufficient information exists about the biological variables that can influence the degree of chemical-induced aneuploidy. In this regard, variables such as dose, solvent, use of gonadotrophins, mode and preovulatory time of chemical administration, time of cell harvest relative to the possibility of chemical-induced meiotic delay, criteria for cytogenetic analysis and data reporting, and an introduction to differences between cell types and sexes are presented. Besides these variables, additional information is needed about the various molecular mechanisms associated with oocyte meiotic maturation and the genesis of aneuploidy. Also, differences between the results from selected chromosome analysis and DNA-hybridization studies are presented. Based upon the various biologic endpoints measured and the differences in cellular physiology and biochemical pathways, agreement among the results from different aneuploidy assays cannot necessarily be expected. To gain further insight into the etiology of aneuploidy in female germ cells, information is needed about the chemical interactions between endogenous and exogenous compounds and those involved with oocyte meiotic maturation.

Chemically-induced aneuploidy in mammalian oocytes

The ability of certain chemicals to elevate the frequency of aneuploidy above spontaneous levels in mammalian experimental models prompts the concern that a similar situation might exist in humans. Validation of experimental models for aneuploidy studies is in progress since there is much to be learned about the causes and mechanisms of chemically-induced aneuploidy. Several biological variables have been shown to influence the results from aneuploidy assays. In this review, we examine these variables as they relate to female germ cell aneuploid assays. Also, we have found that the aneuploidy results obtained from different cell types, sexes, and experimental models cannot necessarily be expected to agree due to certain anatomic and physiologic differences and the end points measured.

Fetal pathology produced by ethylene oxide treatment of the murine zygote

Exposure of female mice to ethylene oxide by inhalation 1 or 6 h after mating produced not only multitemporal death of conceptuses but also high rates of abnormalities among surviving fetuses. In contrast, only marginal effects were observed when females were exposed 9 or 25 h after mating. The abnormalities found among 17 day gestation live fetuses were predominated by hydrops and eye defects, which, together, constitute 54% of all anomalies. Most of the remaining anomalies were distributed among 5 other types: small size, cleft palate, and cardiac, abdominal wall, or extremity and/or tail defects. In a follow-up study, the fetuses of females treated 6 h postmating were examined at 11-15 days gestation and the progression of fetal death and of malformations was studied. Results indicate that the expression of most fetal anomalies does not become apparent until late in gestation. Several of these induced anomalies are similar to common human sporadic birth defects. This new class of experimentally induced fetal anomalies provides a new avenue for investigating zygotic biology and a system for studying the progression of aberrant development.

Chromosome malsegregation and embryonic lethality induced by treatment of normally ovulated mouse oocytes with nocodazole

The mouse egg is ovulated with its nucleus arrested at the metaphase-II stage of meiosis. Sperm entry triggers the completion of the second meiotic division. It has been speculated that damage to the meiotic spindle of normally ovulated eggs at around the time of sperm entry could result in chromosome malsegregation and the death of conceptuses with numerical chromosome anomalies. This hypothesis was tested using nocodazole, a microtubule inhibitor. Nocodazole was administered either to maturing preovulatory oocytes or to normally ovulated eggs at one of the following stages: (1) the time of sperm entry, (2) early pronuclear stage, (3) pronuclear DNA synthesis, (4) prior to first cleavage division, (5) early 2-cell stage, or (6) prior to the second cleavage division. Little or no effect was observed for treatment times other than the time of sperm entry, when the egg is being activated to complete the second meiotic division. Remarkably high frequencies of embryonic lethality, expressed at around the time of implantation, were induced at this stage. Cytogenetic analysis of first cleavage metaphases of zygotes treated at the time of sperm entry revealed a high incidence of varied numerical chromosome anomalies, with changes in ploidy being predominant.

Hypoploidy and hyperplasia in the developing brain exposed to alcohol in utero

Prenatal effects of acute maternal alcohol ingestion on chromosome segregation and mitotic frequency in the brain cells of the fetus were evaluated in mice by direct chromosome and mitotic counts and by flow cytometry. Fetuses were exposed to acute transplacental doses of alcohol for 4 days and killed on the fifth day. Those litters in which the fetuses were developed to the equivalent of normal 16th-17th-day gestation age were analyzed. A marked increase in the number of hypoploid metaphases was observed in direct proportion to the dose ingested by the mother. An over 30% increase in hypoploidy over controls was measured in the fetuses exposed to the highest dose. Counts of mitotic cells showed an over tenfold increase in the mitotic index of the fetal brain exposed to alcohol. Flow cytometric measurements of DNA content in isolated fetal brain cell nuclei showed a shift from a single G0/G1 peak in controls to a bimodal G0/G1-G2 + M distribution in alcohol-exposed fetuses of the same developmental age.

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC Working Paper No. 15/1. Genetic effects of ethanol

Alcoholics have a higher frequency of chromosomal aberrations and sister-chromatid exchanges (SCEs) in their peripheral lymphocytes. In human and mammalian cells in vitro, ethanol generally does not induce genetic damage, but it induces SCEs in the presence of an exogenous metabolic system. In human lymphocytes in vitro, ethanol induces SCEs in the presence of alcohol dehydrogenase. In animals in vivo, ethanol induces a variety of genetic effects, including SCEs, micronuclei, dominant lethal mutations and aneuploidy in mouse eggs. There is some indication that ethanol may lead to genetic damage in sperm. In bacteria, ethanol is at best marginally active. Ethanol leads to anomalous chromosome segregation in Aspergillus, to mutations in yeast, to chromosomal aberrations and SCEs in plant root tips and to disturbances of meiosis and micronuclei in tetrads in Zea and Tradescantia respectively. The first metabolite of ethanol, acetaldehyde is mutagenic in a variety of test systems. The mutagenic activity of acetaldehyde in bacteria is questionable, but there is no doubt of its mutagenic activity in a variety of eukaryotic test systems in vitro as well as in vivo.

Exposure of female mice to ethylene oxide within hours after mating leads to fetal malformation and death

When previously mated female mice were exposed to inhaled ethylene oxide at the time of fertilization of their eggs or during early pronuclear stage of the zygote (before DNA synthesis), a high incidence of mortality among conceptuses and of congenital abnormalities among both the dead and the surviving fetuses was observed. The developmental stage at which death occurred ranged from near the time of implantation to day 17 of gestation when examination of the uterine contents was performed. In comparison, midgestation and late fetal deaths were absent or minimal when the females were exposed either before mating or when conceptuses were in later zygotic stages (pronuclear DNA synthesis) or had reached the early two-cell stage. The random types of congenital abnormality observed and the remarkable stage-dependent sensitivity suggest a genetic basis for the response. The effects differ, both from genetic damages induced in premating germ cells, which lead only to death near the time of implantation, and from teratogenic damage, which leads to malformations only when exposure of embryos occurs during the period of major organogenesis.

An hypothesis regarding the origin of aneuploidy in man: indirect evidence from an experimental model

Recent studies have clearly demonstrated that aneuploidy may be induced in about 10 to 20% of oocytes and recently ovulated eggs when female mice are given an intragastric injection of a dilute solution of ethanol. Similar rates of aneuploidy have also been observed when recently ovulated eggs are briefly exposed in vitro to a dilute solution of ethanol in tissue culture medium. These findings are briefly reviewed, and observations made on the possible underlying mechanism of induction of chromosome malsegregation in the ethanol exposed groups. Attention is drawn to evidence from a wide range of studies on the effect of ethanol, acetaldehyde (its primary metabolite), and anaesthetics on cell division and chromosome segregation in an attempt to substantiate an hypothesis regarding the mode of action of these agents. In the light of this information, it is hypothesised that exposure to ethanol probably interferes with the normal functioning of the cytoskeletal elements of the spindle apparatus, or its precursor elements, during the first or second meiotic divisions. An attempt is also made to account for the very high incidence of aneuploid conceptuses in man, a high proportion of which are spontaneously aborted. It is hypothesised that exposure to ethanol and other spindle active agents during appropriate stages of oogenesis (in particular during the first meiotic division), and possibly also during spermatogenesis, may be important aetiological factors in a proportion of those cases of spontaneous abortion with a numerical chromosome anomaly for which no other obvious cause is recognised. If it is valid to extrapolate from these experimental findings to the clinical situation in man, it is suggested that attention should also be drawn to the potentially greater hazard to the conceptus which could result from maternal alcohol consumption at and shortly before conception.