Relationship between the Length of Sperm Tail Mitochondrial Sheath and Fertility Traits in Boars Used for Artificial Insemination.

Karl Kerns,Julie Robinson,Peter Sutovsky,Amanda Minton,Jennifer Jankovitz,Chris Kuster

doi:10.3390/antiox9111033

Abstract

The length of sperm tail midpiece, occupied by the mitochondrial sheath (MS), has been correlated with reproductive traits of mice, fish, and birds; however, it is not known whether such a correlation exists in higher order species such as domestic pigs. As the mitochondria provide for sperm motility and generate the fertility-affecting reactive oxygen species (ROS), we hypothesized that MS length correlates with boar semen parameters and artificial insemination (AI) fertility. Sperm samples collected from 57 boars and used for single sire AI were labeled with ProteoStat Aggresome probe (AGG; Enzo Life Sciences) for MS imaging by epifluorescence microscopy and image-based flow cytometry (IBFC). The mean boar MS length was 7.26 ± 0.2 µm, ranging from 6.94 ± 0.18 µm to 7.65 ± 0.31 µm. The absolute longest MS measured was 9.19 µm and the shortest was 5.83 µm. Boars in the high tertile of MS length had significantly higher conception rate (CR; p = 0.05) and sperm parameters. Boars within the high tertile of average number piglets born per litter had significantly shorter MS and more varied MS length than boars in the low tertile (p = 0.04). MS length data correlated with conventional sperm parameters including percent viable and intact acrosomes (p = 0.03), basal:induced oxidation ratio (measure of intracellular ROS levels; p = 0.02) and Comp DNA (chromatin integrity; p = 0.06) along with many flow cytometric AGG parameters in IBFC. Sperm head AGG intensity median absolute deviation had a negative correlation with total born (r = −0.423 p = 0.004). These data reveal a complex relationship between sperm MS length and aggresome abundance to sperm parameters and boar reproductive success in AI service.

Highlights

Mammalian spermatozoa carry several dozens of mitochondria organized into a mitochondrial sheath (MS), a helical structure wrapped around the sperm tail midpiece
We developed a new technique for measurement of MS parameters based on the detection of aggresomes, the ubiquitinated protein aggregates that accumulate in the MS of mammalian spermatozoa
Examining relevant sperm traits in domestic boars with extensive fertility records, we found a negative correlation between mean sperm MS length and total number of piglets born per litter (SD Table 3, r = −0.299, p = 0.046), meaning that as the average MS length increased, fewer offspring were born per litter

Summary

Introduction

Mammalian spermatozoa carry several dozens of mitochondria organized into a mitochondrial sheath (MS), a helical structure wrapped around the sperm tail midpiece. Length of sperm tail midpiece, occupied by the MS has been shown to correlate with reproductive traits in deer mice [1], as well as in domestic mice [2], salmon fish [3] and passerine birds [4]. It is not known whether this could be the case in domestic animals positioned higher on phylogenetic tree such as boars and bulls, and if so, whether such a parameter could be used as a fertility marker. Fertility in AI is of paramount importance to agriculture and food production, and potentially relevant to human reproductive health and assisted reproductive therapy

Methods

Results

Conclusion