Presence of endogenous nicks in DNA of ejaculated human spermatozoa and its relationship to chromomycin A3 accessibility

Abstract

During spermiogenesis, mammalian chromatin undergoes replacement of nuclear histones by protamines, resulting in a DNA that is highly condensed in the mature sperm. We have previously demonstrated that a percentage of human spermatozoa exhibit 1) positivity to the guanine-cylosine-specific chromomycin A3 (CMA3) fluorochrome and 2) the presence of endogenous nicks in their DNA. In situ protamination of mature human sperm limits the percentage of sperm positive to CMA3 and exhibiting endogenous nicks. In this study, we report further investigations that aim to clarify the relationship existing between levels of CMA4 stainability and the presence of endogenous nicks in the DNA of mature human spermatozoa. Human spermatozoa from 25 different samples showed values of sensitivity to the CMA3 fluorochrome ranging from 13% to 75%. The same samples showed a percentage of sensitivity to endogenous nick translation ranging from 1% to 38%. A strong correlation (r = 0.86) was evident between these two parameters. Prior staining of sperm with the CMA3 fluorochrome drastically reduced sensitivity to nick translation. In contrast, previously nick-translated sperm stained with CMA3 showed very little difference from samples that had not been pretreated. The presence of nicked sperm in the ejaculate may indicate anomalies during spermiogenesis and be an indicator of male infertility.