Dense spermatozoa in stallion ejaculates contain lower concentrations of mRNAs encoding the sperm specific calcium channel 1, ornithine decarboxylase antizyme 3, aromatase, and estrogen receptor alpha than less dense spermatozoa.

The research article focuses on identifying the differences in concentrations of specific mRNAs found in dense vs. less dense stallion sperm. Findings from the study reveal that dense sperm contain lower amounts of encoded mRNAs related to fertility compared to less dense sperm.

Context and Background

• The study was prompted by the fact that about 15% of both stallions and human males display normal semen parameters but suffer from subfertility. This discrepancy highlights the need for more nuanced analyses of sperm function.
• Density gradient centrifugation is a process which separates dense sperm from less dense sperm and is a method used to enhance fertilization potential in both humans and stallions.

Methods

• Seven adult stallions with normal reproductive capabilities were chosen for the study.
• Both dense and less dense sperm were isolated from individual ejaculates by using density gradient centrifugation. The RNA extracted from the sperm was found to be naturally fragmented into lengths of approximately 250 bases – an observation that aligns with existing reports pertaining to sperm RNA in other species.
• The potential for genomic DNA contamination was eliminated through DNAse treatment of the RNA extracted from the sperm.
• Quantifying the concentrations of certain mRNAs associated with fertility in humans and bulls, was achieved by using reverse transcription polymerase chain reaction (RT-PCR).

Results

• Upon comparing the mRNA concentrations in dense and less dense sperm, the researchers found that the concentrations of four specific mRNAs (encoding the sperm-specific calcium channel, ornithine decarboxylase antizyme 3, aromatase, and estrogen receptor alpha) were two to four times lower in dense sperm than in less dense spermatozoa.
• Interestingly, the concentrations of three other mRNAs which encode different proteins – PRM1, HSPA8, and DNAJC4 – showed no differences in concentration between dense sperm and less dense counterparts.
• These differences in mRNA concentrations among dense and less dense sperm populations highlight previously unidentified variations that open avenues for further research.