Spermatozoal transcriptome profiling for bull sperm motility: a potential tool to evaluate semen quality

Regarding bull fertility, establishing an association between in vitro findings and field fertility requires a multi-parametric approach that measures the integrity of various structures and dynamic functions, such as motion characteristics, among others. The heterogeneous RNA pattern of spermatozoa could be used in genomic analysis for evaluating both spermatogenesis and fertility potential of semen, mainly because of the static status of the transcriptome of this particular differentiated cell. In a previous study, we determined that some spermatozoal transcripts identified by PCR-based cDNA subtraction are associated with non-return rate, a field fertility index. In the present study, the microarray technology was used in conjunction with differential RNA transcript extraction. We have shown that among these genes, some transcripts are also associated with the motility status of a population of sperm cells fractionated from the same ejaculate. We highlighted a systematic data analysis and validation scheme important for the identification of significant transcripts in this context. With such an approach, we found that transcripts encoding a serine/threonine testis-specific protein kinase (TSSK6) and a metalloproteinase non coding RNA (ADAM5P) are associated with high-motility status (P<0.001), also confirmed by quantitative PCR (P=0.0075). This association was found only when transcripts were extracted using the hot-TRIzol protocol, whereas the cold-TRIzol RNA extract comprised mitochondrial transcripts. These results demonstrate that some transcripts previously identified in association with field fertility are also found associated with in vitro motility provided that a stringent RNA extraction protocol is used.