Transcriptome analysis of bull spermatozoa: implications for male fertility

Spermatozoa deliver more than the paternal genome into the oocyte; they also carry remnant messenger RNA from spermatogenesis. The RNA profiles of spermatozoa from high-fertility and a low-fertility Holstein bulls were analysed using Affymetrix bovine genechips. A total of 415 transcripts out of approximately 24,000 were differentially detected in spermatozoa collected from both bulls (fold change ⩾2.0; P < 0.01). These transcripts were associated with different cellular functions and biological processes. Spermatozoa from high-fertility bulls contained higher concentrations of transcripts for membrane and extracellular space protein locations, while spermatozoa from the low-fertility bulls were deficient of transcripts for transcriptional and translational factors. Quantitative real-time PCR was used on three low-fertility and four high-fertility bulls to validate the microarray data. Two highly represented transcripts in the microarray analysis (protamine 1 and casein beta 2) were validated, as well as a third transcript (thrombospondin receptor CD36 molecule) that showed a lower concentration in low-fertility bulls. This study presents the global analysis of spermatozoa originating from bulls with opposite fertility. These results provide some specific transcripts in spermatozoa that could be associated with bull fertility.Male fertility, ability of the sperm to fertilize the oocyte and support early embryonic development, is one of the most important factors in mammalian reproduction, and it has a significant impact on human health. Fertility evaluation of the male is essential for understanding the causes of poor quality semen and its specific effects on fertility. This study demonstrates that in addition to providing half of the genomic material, spermatozoa also contribute transcripts to the oocyte. The spectrum of mRNA molecules found in spermatozoa of high and low fertility bulls suggests potential roles for a number of these spermatozoa transcripts in fertilization and early embryonic development in mammals.