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

Abstract

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.

Fig. 1

AZFc region is located in repeated DNA blocks (amplicons), different markers present in this region. The figure is showing STS markers selected for study in this region. The selected STS markers include SY 1206 and SY 1197 markers used as hot spots to radiation and SY579 marker as a possible unstable marker in DAZ gene

Fig. 2

Standard curves showing PCR efficiencies of target and reference genes as well as the slope of the fit lines within the acceptable range of −3.6 < slope <−3.1

Fig. 3

Amplification plot and CT value of SY 1197, 1206 and 579 markers before radiation (a) and after exposure to 4 Gy radiation (b) in a typical sample (A6). This sample had amplification in SY 1197, 1206 markers and microdeletion in SY579 marker

Fig. 4

Mean total frequency of microdeletion and amplification observed in three study groups (normal, oligozoospermia and azoospermia) following different doses (2 and 4 Gy) of radiation. Error bars show standard deviation of mean values