Commercial application of flow cytometry for evaluating bull sperm

Structural Analysis of Sperm Centrioles Using N-STORM

A prominent technical barrier when imaging swimming sperm is capturing a singular sperm cell's head and tail position simultaneously at a high resolution to understand their relationship in different stages of the sperm tail beating cycle. This is due to the sperm's high beating frequency, rotational movement, and the large difference in diameter between the head and tail. These intricacies increase the complexity of determining the position of a dynamic subcellular structure in the sperm neck, such as the centriole. We have developed a way to obtain this information by snap freezing mobile sperm at different stages of the sperm tail beating cycle and then analyzing them with super-resolution microscopy. This method captures the position of both the sperm head and tail at the microscale and centriolar substructure details at the nanoscale. This chapter describes the detailed procedures for the selection, preparation, antibody staining, 3D N-STORM imaging, and image quantification of bovine spermatozoa.

Bull Sperm SWATH-MS-Based Proteomics Reveals Link between High Fertility and Energy Production, Motility Structures, and Sperm-Oocyte Interaction

The prediction of male or semen fertility potential remains a persistent challenge that has yet to be fully resolved. This work analyzed several in vitro parameters and proteome of spermatozoa in bulls cataloged as high- (HF; n = 5) and low-field (LF; n = 5) fertility after more than a thousand artificial inseminations. Sperm motility was evaluated by computer-assisted sperm analysis. Sperm viability, mitochondrial membrane potential (MMP) and reactive oxygen species (mROS) of spermatozoa were assessed by flow cytometry. Proteome was evaluated by the SWATH-MS procedure. Spermatozoa of HF bulls showed significantly higher total motility than the LF group (41.4% vs 29.7%). Rates of healthy sperm (live, high MMP, and low mROS) for HF and LF bull groups were 49% and 43%, respectively (p > 0.05). Spermatozoa of HF bulls showed a higher presence of differentially abundant proteins (DAPs) related to both energy production (COX7C), mainly the OXPHOS pathway, and the development of structures linked with the motility process (TPPP2, SSMEM1, and SPAG16). Furthermore, we observed that equatorin (EQTN), together with other DAPs related to the interaction with the oocyte, was overrepresented in HF bull spermatozoa. The biological processes related to protein processing, catabolism, and protein folding were found to be overrepresented in LF bull sperm in which the HSP90AA1 chaperone was identified as the most DAP. Data are available via ProteomeXchange with identifier PXD042286.

Abnormal centriolar biomarker ratios correlate with unexplained bull artificial insemination subfertility: a pilot study

The mechanisms underlying male infertility are poorly understood. Most mammalian spermatozoa have two centrioles: the typical barrel-shaped proximal centriole (PC) and the atypical fan-like distal centriole (DC) connected to the axoneme (Ax). These structures are essential for fertility. However, the relationship between centriole quality and subfertility (reduced fertility) is not well established. Here, we tested the hypothesis that assessing sperm centriole quality can identify cattle subfertility. By comparing sperm from 25 fertile and 6 subfertile bulls, all with normal semen analyses, we found that unexplained subfertility and lower sire conception rates (pregnancy rate from artificial insemination in cattle) correlate with abnormal centriolar biomarker distribution. Fluorescence-based Ratiometric Analysis of Sperm Centrioles (FRAC) found only four fertile bulls (4/25, 16%) had positive FRAC tests (having one or more mean FRAC ratios outside of the distribution range in a group's high-quality sperm population), whereas all of the subfertile bulls (6/6, 100%) had positive FRAC tests (P = 0.00008). The most sensitive biomarker was acetylated tubulin, which had a novel labeling pattern between the DC and Ax. These data suggest that FRAC and acetylated tubulin labeling can identify bull subfertility that remains undetected by current methods and may provide insight into a novel mechanism of subfertility.

Assessment of the stallion sperm acrosome in two different extenders: Spermac stain in comparison with PNA/PSA/PI triple-staining

Since the stallion acrosome is very small compared to other species and cannot be properly assessed without additional staining, several labelling techniques were developed to facilitate its assessment. The aim of this study was to compare the Spermac stain (Minitüb GmbH) and a PNA/PSA/PI triple-staining detected by flow cytometry with regard to method agreement for detecting non-intact acrosomes within two different extenders. For this purpose, eighteen stallion ejaculates were split in half and diluted with the semen extenders EquiPlus or Gent (Minitüb GmbH) to a final concentration of 50 × 106  sperm/mL, respectively. Subsequently, 126 semen samples were stained with both methods between 4 and 240 h (mean: 63.8 ± 48.9 h) after semen collection. Calculated Intraclass correlation coefficients revealed excellent correlations between both methods for EquiPlus (r = .77, p < .001) and fair correlations for Gent (r = .49, p < .001). Interestingly, flow cytometry detected more non-intact acrosomes in EquiPlus than in Gent (p < .001), whereas the Spermac stain showed no differences (p = .902) between extenders. The poorer method agreement in Gent could be caused by egg yolk artefacts, which made interpretation difficult, so flow cytometry might be preferred. The differences in detected non-intact acrosomes between extenders highlighted the importance of establishing adapted laboratory protocols for different extender types in order to generate comparable results.