Morphologically normal sperm have significantly greater total-RNA content than abnormal sperm

Abstract

Introduction: Previous studies have demonstrated the presence of ribonucleic acid (RNA) in mature, ejaculated sperm and that sperm with poor motility have significantly more RNA than good motility sperm. However, no studies have investigated the relationship between RNA content and sperm morphology. Therefore, the study objective was to determine the relationship between total RNA content and sperm morphology. Methods: Sperm samples were separated by density centrifugation (Promotor, CERES Fertility, San Diego, CA) into morphologically normal and abnormal populations. Sperm morphology scores were determined by strict criteria. Total RNA was extracted from sperm via the Roche (Indianapolis, IN, USA) RNA isolation kit. Total RNA (μg of RNA per million sperm cells) recovered per sperm population from each ejaculate was determined by spectrophotometer and calculated as follows: (absorbance at 260 nm)×(conversion factor)×(dilution factor). The conversion factor for RNA is 0.04 μg/μl per optical density unit at 260 nm. Total RNA purity was calculated as the absorbance at 260 nm divided by the absorbance at 280 nm. Data were analyzed by Student's t-test. Results: A total of 179 semen specimens from different men underwent RNA extraction and analysis as described. All samples had absorbance readings between 0.1 and 1.0 at 260 nm and were determined to be accurate. Total RNA purity estimates for all samples were within the acceptable ratio of 1.7 and 1.9. RNA content in morphologically normal sperm (2.83±0.14 μg/10 6 cells) was significantly higher ( P<0.05) than the amount found in morphologically abnormal sperm (2.26±0.23 μg/10 6 cells). Conclusions: Ribonucleic acid content is significantly lower in morphologically abnormal sperm. Morphologically abnormal sperm may have impaired transcriptional and, or translational pathways thus negatively impacting cell function.