Sperm rDNA Copy Number and Methylation Are Associated with Male-Factor Infertility.

Area of Science:

• Reproductive Biology
• Genetics
• Epigenetics

Background:

• Ribosomal DNA (rDNA) copy number (CN) in human sperm is highly variable.
• The activity of rDNA, indicated by promoter hypomethylation, is crucial for its function.
• Individual differences in rDNA CN and activity may impact male fertility.

Purpose of the Study:

• To quantify absolute and presumably active rDNA CN in sperm from individuals with normal versus abnormal semen parameters.
• To investigate the association between rDNA CN, promoter methylation, and fertility outcomes after in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI).
• To explore the potential role of sperm rDNA CN in idiopathic male infertility.

Main Methods:

• Utilized droplet digital PCR and deep bisulfite sequencing to measure absolute and active rDNA CN.
• Analyzed sperm samples from 190 individuals, categorized by semen quality and IVF/ICSI pregnancy outcomes.
• Assessed promoter methylation levels in relation to rDNA CN and semen parameters.

Main Results:

• Abnormal semen parameter (ASP) samples showed significantly lower presumably active rDNA CN (104 ± 31) compared to normal samples (NSP) (115 ± 31).
• Increased promoter methylation was observed in ASPs (13.9%) versus NSPs (12.1%).
• Sperm samples not leading to pregnancy had lower absolute (225 ± 51) and active rDNA CN (103 ± 30) than those resulting in pregnancy (249 ± 62 and 115 ± 31, respectively).

Conclusions:

• Sperm rDNA CN, both absolute and active, may be a key factor influencing idiopathic male infertility.
• A higher active rDNA CN in normozoospermic males correlates with successful pregnancy outcomes.
• Approximately 60 active sperm rDNA copies appear sufficient for establishing pregnancy, highlighting their importance in reproductive success.