Griseofulvin-induced aneuploidy and meiotic delay in male mouse germ cells: detected by using conventional cytogenetics and three-color FISH

Chemically induced aneuploidy in germ cells. Part II of the report of the 2017 IWGT workgroup on assessing the risk of aneugens for carcinogenesis and hereditary diseases

As part of the 7th International Workshops on Genotoxicity Testing held in Tokyo, Japan in November 2017, a workgroup of experts reviewed and assessed the risk of aneugens for human health. The present manuscript is one of three manuscripts from the workgroup and reports on the unanimous consensus reached on the evidence for aneugens affecting germ cells, their mechanisms of action and role in hereditary diseases. There are 24 chemicals with strong or sufficient evidence for germ cell aneugenicity providing robust support for the ability of chemicals to induce germ cell aneuploidy. Interference with microtubule dynamics or inhibition of topoisomerase II function are clear characteristics of germ cell aneugens. Although there are mechanisms of chromosome segregation that are unique to germ cells, there is currently no evidence for germ cell-specific aneugens. However, the available data are heavily skewed toward chemicals that are aneugenic in somatic cells. Development of high-throughput screening assays in suitable animal models for exploring additional targets for aneuploidy induction, such as meiosis-specific proteins, and to prioritize chemicals for the potential to be germ cell aneugens is encouraged. Evidence in animal models support that: oocytes are more sensitive than spermatocytes and somatic cells to aneugens; exposure to aneugens leads to aneuploid conceptuses; and, the frequencies of aneuploidy are similar in germ cells and zygotes. Although aneuploidy in germ cells is a significant cause of infertility and pregnancy loss in humans, there is currently limited evidence that aneugens induce hereditary diseases in human populations because the great majority of aneuploid conceptuses die in utero. Overall, the present work underscores the importance of protecting the human population from exposure to chemicals that can induce aneuploidy in germ cells that, in contrast to carcinogenicity, is directly linked to an adverse outcome.

Specific deletion of Cdh2 in Sertoli cells leads to altered meiotic progression and subfertility of mice

CDH2 (cadherin 2, Neural-cadherin, or N-cadherin) is the predominant protein of testicular basal ectoplasmic specializations (basal ES; a testis-specific type of adhesion junction), one of the major cell junctions composing the blood-testis barrier (BTB). The BTB is found between adjacent Sertoli cells in seminiferous tubules, which divides the tubules into basal and adluminal compartments and prevents the deleterious exchange of macromolecules between blood and seminiferous tubules. However, the exact roles of basal ES protein CDH2 in BTB function and spermatogenesis is still unknown. We thus generated mice with Cdh2 specifically knocked out in Sertoli cells by crossing Cdh2 loxP mice with Amh-Cre mice. Cdh2 deletion in Sertoli cells did not affect Sertoli cell counts, but led to compromised BTB function, delayed meiotic progression from prophase to metaphase I in testes, increased germ cell apoptosis, sloughing of meiotic cells, and, subsequently, reduced sperm counts in epididymides and subfertility of mice. However, the testes with Cdh2-specific deletion in germ cells did not show any difference from the normal control testes, and phenotypes observed in Sertoli cell and germ cell Cdh2 double-knockout mice were indistinguishable from those in mice with Cdh2 specifically knocked out only in Sertoli cells. Taken together, our data demonstrate that the adhesion junction component, Cdh2, functions just in Sertoli cells, but not in germ cells during spermatogenesis, and is essential for the integrity of BTB function, its deletion in Sertoli cells would lead to the BTB damage and subsequently meiosis and spermatogenesis failure.

Effects of griseofulvin on in vitro porcine oocyte maturation and embryo development

Griseofulvin is an orally administered antifungal drug that affects microtubule formation in vitro and interferes with microtubule dynamics in vivo as clearly shown for mitotic cells in several cell systems. This article reports the effects of griseofulvin on in vitro maturation of porcine oocytes and subsequent effects on embryo development. Our results revealed a concentration-dependent effect on meiotic spindles with 20-40 μM griseofulvin affecting oocyte maturation, and 40 μM affecting fertilization and embryo development. These concentrations of griseofulvin did not affect mitochondrial and cortical granule distribution that also depend on microtubule and cytoskeletal functions during oocyte maturation. Specific effects on the meiotic spindle included spindle disorganization and aberrant chromosome separation displayed as prominent chromosome clusters in oocytes treated with 40 μM griseofulvin. These results strongly suggested that griseofulvin affected porcine oocyte in vitro maturation and following embryo development by disturbing microtubule dynamics.

The use of fluorescent in situ hybridization in male infertility

Male factors are implicated in up to 50% of couples being evaluated and treated for infertility with advanced assisted reproductive technologies. Genetic abnormalities, including sperm chromosome aneuploidy as well as structural aberrations, are one of the major causes of infertility. The use of chromosome-specific DNA probes labeled with fluorochromes, particularly the combination with multiple probes, has been used to indirectly study the sperm chromosome by fluorescent in situ hybridization (FISH). Clinically, this technique is also used to assess the sperm of men recovering from gonadotoxic treatment. Recent advances in this technology facilitate the evaluation of sperm aneuploidy. Sperm FISH is a widely used screening tool to aid in counseling couples with severe male factor infertility, especially in cases of prior repeated in vitro fertilization/intracytoplasmic sperm injection failure or recurrent pregnancy loss. Automation of FISH imaging and analysis, as well as the development of emerging techniques such as comparative genomic hybridization, will all contribute to the promise of future diagnostic approaches aimed at improving the quality, ease, and efficiency of aneuploidy analysis.

Analysis of sperm karyotypes in a patient treated with griseofulvin

Griseofulvin is known to interfere with chromosome segregation by binding to microtubule-associated proteins. Studies in mouse germ cells have demonstrated that griseofulvin can induce aneuploidy (numerical chromosome abnormalities) at therapeutic concentrations. The aim of this study was to determine if chronic griseofulvin treatment led to an increased frequency of sperm chromosome abnormalities in one male subject. We analyzed 290 full sperm karyotypes using the human sperm-hamster oocyte fusion system. The frequency of X- and Y-bearing sperm was equal. There was no increase in the frequency of numerical (1.7%) or structural (9.3%) abnormalities in the subject compared to unexposed controls. Although reassuring, this is the first report on this subject and future studies are needed to assess the risk of griseofulvin.

Gender differences in germ-cell mutagenesis and genetic risk

Current international classification systems for chemical mutagens are hazard-based rather than aimed at assessing risks quantitatively. In the past, germ-cell tests have been mainly performed with a limited number of somatic cell mutagens, and rarely under conditions aimed at comparing gender-specific differences in susceptibility to mutagen exposures. There are profound differences in the genetic constitution, and in hormonal, structural, and functional aspects of differentiation and control of gametogenesis between the sexes. A critical review of the literature suggests that these differences may have a profound impact on the relative susceptibility, stage of highest sensitivity and the relative risk for the genesis of gene mutation, as well as structural and numerical chromosomal aberrations in male and female germ cells. Transmission of germ-cell mutations to the offspring may also encounter gender-specific influences. Gender differences in susceptibility to chemically derived alterations in imprinting patterns may pose a threat for the health of the offspring and may also be transmitted to future generations. Recent reports on different genetic effects from high acute and from chronic low-dose exposures challenge the validity of conclusions drawn from standard methods of mutagenicity testing. In conclusion, research is urgently needed to identify genetic hazards for a larger range of chemical compounds, including those suspected to disturb proper chromosome segregation. Alterations in epigenetic programming and their health consequences will have to be investigated. More attention should be paid to gender-specific genetic effects. Finally, the database for germ-cell mutagens should be enlarged using molecular methodologies, and genetic epidemiology studies should be performed with these techniques to verify human genetic risk.

Gender effects on the incidence of aneuploidy in mammalian germ cells

Aneuploidy occurs in 0.3% of newborns, 4% of stillbirths, and more than 35% of all human spontaneous abortions. Human gametogenesis is uniquely and gender-specific susceptible to errors in chromosome segregation. Overall, between 1% and 4% of sperm and as many as 20% of human oocytes have been estimated by molecular cytogenetic analysis to be aneuploid. Maternal age remains the paramount aetiological factor associated with human aneuploidy. The majority of extra chromosomes in trisomic offspring appears to be of maternal origin resulting from nondisjunction of homologous chromosomes during the first meiotic division. Differences in the recombination patterns between male and female meiosis may partly account for the striking gender- and chromosome-specific differences in the genesis of human aneuploidy, especially in aged oocytes. Nondisjunction of entire chromosomes during meiosis I as well as premature separation of sister chromatids or homologues prior to meiotic anaphase can contribute to aneuploidy. During meiosis, checkpoints at meiotic prophase and the spindle checkpoint at M-phase can induce meiotic arrest and/or cell death in case of disturbances in pairing/recombination or spindle attachment of chromosomes. It has been suggested that gender differences in aneuploidy may result from more permissive checkpoints in females than males. Furthermore, age-related loss of chromosome cohesion in oocytes as a cause of aneuploidy may be female-specific. Comparative data about the susceptibility of human male and female germ cells to aneuploidy-causing chemicals is lacking. Increases of aneuploidy frequency in sperm have been shown after exposure to therapeutic drugs, occupational agents and lifestyle factors. Conversely, data on oocyte aneuploidy caused by exogenous agents is limited because of the small numbers of oocytes available for analysis combined with potential maternal age effects. The vast majority of animal studies on aneuploidy induction in germ cells represent cause and effect data. Specific studies designed to evaluate possible gender differences in induction of germ cell aneuploidy have not been found. However, the comparison of rodent data available from different laboratories suggests that oocytes are more sensitive than male germ cells when exposed to chemicals that effect the meiotic spindle. Only recently, in vitro experiments, analyses of transgenic animals and knockdown of expression of meiotic genes have started to address the molecular mechanisms underlying chromosome missegregation in mammalian germ cells whereby striking differences between genders could be shown. Such information is needed to clarify the extent and the mechanisms of gender effects, including possible differential susceptibility to environmental agents.

Mechanisms and chemical induction of aneuploidy in rodent germ cells

The objective of this review is to suggest that the advances being made in our understanding of the molecular events surrounding chromosome segregation in non-mammalian and somatic cell models be considered when designing experiments for studying aneuploidy in mammalian germ cells. Accurate chromosome segregation requires the temporal control and unique interactions among a vast array of proteins and cellular organelles. Abnormal function and temporal disarray among these, and others to be identified, biochemical reactions and cellular organelles have the potential for predisposing cells to aneuploidy. Although numerous studies have demonstrated that certain chemicals (mainly those that alter microtubule function) can induce aneuploidy in mammalian germ cells, it seems relevant to point out that such data can be influenced by gender, meiotic stage, and time of cell-fixation post-treatment. Additionally, a consensus has not been reached regarding which of several germ cell aneuploidy assays most accurately reflects the human condition. More recent studies have shown that certain kinase, phosphatase, proteasome, and topoisomerase inhibitors can also induce aneuploidy in rodent germ cells. We suggest that molecular approaches be prudently incorporated into mammalian germ cell aneuploidy research in order to eventually understand the causes and mechanisms of human aneuploidy. Such an enormous undertaking would benefit from collaboration among scientists representing several disciplines.

Veterinary pharmacovigilance. Part 6. Predictability of adverse reactions in animals from laboratory toxicology studies

Toxicological studies are conducted on constituents of veterinary medicinal products for a number of reasons. Aside from being a requirement of legislation, they are carried out for predictive purposes in the assessment of user safety or for the determination of consumer safety, for example, in the elaboration of maximum residue limits or tolerances. Alternatively, the results of toxicology studies may be available as they have been generated for registration of the drug for human medicinal purposes. This paper examines if the results of such studies have any predictive value for adverse reactions, which might occur during clinical use in animals. A number of adverse reactions, notably the Type A (toxicology or pharmacology dependent) should be predictable from these laboratory studies. However, as with human pharmaceutical products, they have less utility in predicting Type-B reactions (idiosyncratic in nature).

Cross-species sperm-FISH assays for chemical testing and assessing paternal risk for chromosomally abnormal pregnancies

The father, like the mother, can transmit genetic defects to his offspring that are detrimental for normal development and a healthy life. Epidemiological studies have identified associations between several paternal exposures and abnormal reproductive outcomes, but these types of studies are inherently complex and expensive, and the risk factors for the paternal contribution to abnormal reproductive outcomes remain poorly understood. Several sensitive methods have been developed for detecting mutations and chromosomal damage directly in sperm. These assays are potential bioindicators for paternal risk factors for infertility, spontaneous abortions, aneuploidy syndromes, and genetic diseases in children. Among these methods, fluorescence in situ hybridization (FISH) has been adapted for the detection of numerical and structural chromosomal abnormalities in the sperm of an expanding number of species, including humans and rodents. Sperm FISH has identified several potential paternal risk factors such as age, drugs, lifestyles, and various environmental/occupational exposures. Here, we summarize the status of the development and usage of these sperm-FISH assays and suggest strategies for prioritizing chemical agents for epidemiological investigations to assess paternal risk for abnormal reproductive outcome.

Influence of Griseofulvin treatment on semen quality in the dog

Griseofulvin is used to treat dermatomycosis in many species and causes oligospermia in supra-pharmacological doses. The aim of the present study was to evaluate the effect of Griseofulvin administered at therapeutic doses upon semen quality in dogs. Four dogs were treated with Griseofulvin (25 mg/kg per day) for 30 days. Semen collections and analyses were performed before, during and for 100 days after treatment for the Griseofulvin group and 10 untreated control dogs. Semen analyses included mean percentage of forward progressively motile sperm, total sperm output, normal live sperm and normal dead sperm. There was no significant difference between control and treated dogs for each of the semen quality parameters. Therapeutic dosage of Griseofulvin had no deleterious effect upon semen quality in dogs, although this does not preclude potential embryotoxic and teratogenic effects.

Induction of aneuploidy in male mouse germ cells detected by the sperm-FISH assay: a review of the present data base

Multicolour fluorescence in situ hybridization (FISH) with chromosome-specific DNA-probes can be used to assess aneuploidy (disomy) and diploidy in sperm of any species provided the DNA-probes are available. In the present EU research project, DNA-probes for mouse chromosomes 8, X and Y were employed each labelled with different colours. Male mice were treated with the test chemicals and sperm were sampled from the Caudae epididymes 22-24 days later to allow spermatocytes exposed during meiosis to develop into mature sperm. At present, the data base comprises 10 chemicals: acrylamide (AA), carbendazim (CB), colchicine (COL), diazepam (DZ), griseofulvin (GF), omeprazole (OM), taxol (TX), thiobendazole (TB), trichlorfon (TF) and vinblastine (VBL). Of these, COL and TF induced disomic sperm only. DZ and GF induced disomic and diploid sperm, while CB and TB induced diploid sperm only. VBL gave contradictory results in repeated experiments in an inter-laboratory comparison. AA, OM and TX did not induce an increase in disomic or diploid sperm at the doses used. The induction of aneuploidy by DZ was also tested in humans. Sperm samples from patients after attempted suicide and from patients with chronic Valium((R)) abuse were evaluated using human DNA-probes specific for chromosomes 1,16, 21, X and Y. A quantitative comparison between mouse and man indicates that male meiosis in humans is 10-100 times more sensitive than in mice to aneuploidy induction by DZ. The positive response of mice to TF supports the hypothesis by Czeizel et al. [Lancet 341 (1993) 539] that TF may be causally related to the occurrence of congenital abnormality clusters in a Hungarian village.

In vivo cytogenetics: mammalian germ cells

This chapter summarizes the most relevant methodologies available for evaluation of cytogenetic damage induced in vivo in mammalian germ cells. Protocols are provided for the following endpoints: numerical and structural chromosome aberrations in secondary oocytes or first-cleavage zygotes, reciprocal translocations in primary spermatocytes, chromosome counting in secondary spermatocytes, numerical and structural chromosome aberrations, and sister chromatid exchanges (SCE) in spermatogonia, micronuclei in early spermatids, aneuploidy in mature sperm. The significance of each methodology is discussed. The contribution of novel molecular cytogenetic approaches to the detection of chromosome damage in rodent germ cells is also considered.