Numerical chromosome abnormalities in 8-cell embryos generated from γ-irradiated male mice in the absence and presence of vitamin E

De novo cytogenetic alterations in spermatozoa of subfertile males might be due to genome instability associated with idiopathic male infertility: Experimental evidences and Review of the literature

Male infertility is caused by many factors including genetics. Although part of genetic damages are inherited and could be traced in blood leukocytes, but those de novo alterations induced in spermatogenesis are not part of diagnostic work up. De novo alterations might be the cause of many idiopathic conditions of male infertility. The aim of this study was to evaluate DNA damage, sex chromosomal aneuploidy and DAZ microdeletion in sperms of subfertile males in comparison with normal healthy individuals. Whole blood and semen samples were obtained from 75 subfertile and 45 normal men. Semen samples from karyotypically normal subfertile and normal individuals were used for DNA fragmentation, sex chromosome aneuploidy and DAZ microdeletion analysis. Sperm DNA damage was assessed by alkaline comet assay, chromosome aneuploidy and DAZ microdeletion was assessed using a combined primed in situ labeling and fluorescent in situ hybridization (PRINS-FISH) method. A significantly high percentage of DNA fragmentation was observed in subfertile patients compared to control. Similar observation was observed for sex chromosome aneuploidy and DAZ microdeletion (p < 0.01). A relatively small interindividual difference was seen in all three assays performed. However DAZ microdeletion was observed as mosaic form in Y bearing sperms. Results indicate that subfertile males experience higher genome instability in spermatogenesis expressed as DNA damage and consequently sperm chromosomal 220 AIMS Genetics Volume 3, Issue 4, 219-238. aneuploidy or microdeletions. Occurrence of de novo genetic alterations caused by environmental chemico-physical genotoxic agents during spermatogenesis might be one of the causes of idiopathic male infertility.

High frequency of de novo DAZ microdeletion in sperm nuclei of subfertile men: possible involvement of genome instability in idiopathic male infertility

The occurrence and diagnosis of Y-chromosome microdeletions, specifically deletions of the DAZ (Deleted in Azoospermia) genes are an important issue in male infertility. Screening Y chromosome microdeletion is mainly done using polymerase chain reaction (PCR) on blood leukocytes. However, there is some evidence indicating that presence of DAZ in somatic cells might not be indicative of its presence in the germ cell lineage. Therefore, a total of 130 men with poor semen quality were examined for presence of DAZ microdeletion in their leukocytes. From these, sperm from 40 randomly selected men with no DAZ microdeletions in their leukocytes (n = 10 oligozoospermia; n = 10 asthenozoospermia; n = 10 oligoasthenozoospermia; and n = 10 near-azoospermia) were were compared to sperm from men of normal semen quality (n = 10) using combined primed in situ labelling and fluorescent in situ hybridization (PRINS-FISH) technique as well as screening for sex chromosome aneuploidy. There was an increased frequency of DAZ microdeletion in blood samples from oligozoospermic (5%) (p < 0.05) and near azoospermic patients (14%) (p < 0.01). A high frequency of DAZ microdeletion was observed in the sperm of patients with no DAZ microdeletion in their leukocytes compared to control (p < 0.01). The frequency of sex chromosome aneuploidy also increased, correlating with the severity of infertility in the studied groups. A similar result was observed for sex chromosome aneuploidy. The results might be indicative of DAZ microdeletion induction during spermatogenesis.

Genome instability in AZFc region on Y chromosome in leukocytes of fertile and infertile individuals following exposure to gamma radiation

PURPOSE

Men are exposed to various doses of ionizing radiation due to living in regions with high natural background radiation, accidentally, occupationally or for cancer treatment. To study genomic instability of AZFc region to gamma radiation, blood samples from normal, oligozoospermia, and azoospermia individuals were irradiated by a Co-60 source.

METHODS

Irradiated cells were kept for 48 h in order to repair initial DNA damages. Real time PCR was performed for three markers (SY 1206, SY 1197, SY 579) for testing copy number variation before and after irradiation. Copy number variations were compared by calculation of cycle threshold comparative method.

RESULTS

Copy number variations of studied markers in AZFc region (microdeletion and duplication) in all samples after exposure to radiation increased with a dose dependent fashion. The frequency of instability was significantly higher in samples from infertile men in comparison with fertile ones (p < 0.001).

CONCLUSION

No significant difference was seen between the two infertile groups (p > 0.05). This observation might be a possible explanation for induction of azoospermia and oligozoospermia after radiotherapy. Increased frequency of induced microdeletion and duplication in infertile men compared with normal might be attributed to the deficiency in repair systems and the genetic factors involved in incomplete spermatogenesis of infertile men.

Increased frequency of micronuclei in lymphocytes of infertile males after exposure to gamma irradiation: a possible sign of genomic instability

PURPOSE

Induced chromosomal instability and micronucleus (MN) formation in blood lymphocytes of infertile men in comparison with fertile men exposed to gamma radiation was investigated.

METHODS

Blood samples of healthy and infertile donors were irradiated by 2 and 4 Gy Co-60 gamma-rays, then cultured in RPMI-1640 complete medium containing 1% phytoheamaglutinin (PHA) and incubated in a CO(2) incubator. Cytochalasin-B was added to the cultures at a final concentration of 4 μg/ml. Finally, harvesting, slide making, and analysis were performed according to standard procedures.

RESULTS

We observed a statistically significant difference between the frequencies of micronuclei in lymphocytes of infertile individuals, compared to healthy donors, before and after exposure to gamma rays. Although higher in azoospermia patients, the frequency of MN was not statistically different between infertile groups.

CONCLUSIONS

This study indicates that genomic instability in infertile men could probably contribute to the development of an impaired reproductive capacity.

Cytogenetic damage in preimplantation mouse embryos generated after paternal and parental gamma-irradiation and the influence of vitamin C

Cytogenetic damage expressed as micronuclei (MN) in 4-8-cell embryos generated after irradiation of male or male and female mice in the absence and presence of vitamin C was investigated. Male NMRI mice were whole body exposed to 4 Gy gamma-rays and mated with non-irradiated superovulated female mice in 6 successive weeks after irradiation in a weekly interval. In experiments involving irradiation of both male and female mice, irradiated male mice for 6 weeks post irradiation were mated with female mice irradiated after induction of superovulation. Effect of 100 mg/kg vitamin C (ascorbic acid) on the frequency of MN was also studied. Pregnant animals were euthanized and embryos flushed from the oviducts and fixed on slides. The rate of MN observed in embryos generated from irradiated male compared with control group dramatically increased (P<0.01). Frequency of MN in this group decreased dramatically after vitamin C treatment (P<0.01). Frequency of MN in embryos generated by mating both male and female irradiated mice was higher than that observed for those embryos generated by irradiated male mice alone. However, a considerable modifying effect of vitamin C was observed for this group too (P<0.05). Results indicate that irradiation of gonads during spermatogenesis and preovulatory stage oocytes may lead to unstable chromosomal aberrations and probably stable chromosomal abnormalities affecting pairing and disjunction of chromosomes in successive preimplantation embryos expressed as MN. The way vitamin C reduces clastogenic effects of radiation on germ cells leading to reduced frequency of MN in pre-embryos might be due to its antioxidation and radical scavenging properties.