Fertilization failure in vivo and in vitro (intracytoplasmic sperm injection, ICSI) can be caused by the inability of sperm to elicit intracellular calcium oscillations and to induce oocyte activation. Phospholipase C zeta (PLCz) is sperm-associated protein that can induce oocyte activation. Male infertility has been associated with PLCz deficiency in various species, although this has not been studied in the stallion. We hypothesised that the location and amount of PLCz on sperm varies among stallions. The aim of this study was to validate commercial antibodies (Ab) to detect PLCz on stallion sperm, and then to use these Ab to quantify the amount of PLCz, using flow cytometry, with the long-term goal of correlating PLCz on sperm with stallion fertility. Frozen-thawed sperm were analysed (20 stallions in 3 replicates) using 2 commercial Ab (anti-mouse PLCz M163 and anti-human PLCz H50, Santa Cruz Biotechnology, TX, USA). Western blot and immunofluorescence microscopy were used to validate Ab binding. For microscopy, sperm DNA was counterstained with 1 µg mL−1 Hoechst 33258. For flow cytometry, samples were incubated with Live Dead Fixable Far Red Stain Kit (Molecular Probes, Eugene, OR, USA), fixed, permeabilized, incubated overnight with primary Ab, and labelled with conjugated secondary Ab (anti-rabbit IgG Alexa Fluor 488, Molecular Probes). Green and far red mean fluorescence intensity (MFI) were measured for 20,000 cells per sample. Results are presented as mean ± SEM. Wilcoxon test, Spearman rank correlation, and linear regression were performed for analyses. Immunoblot analyses for both commercial Ab identified an immunoreactive band of ~70 kDa in sperm heads, tails, and whole sperm; β-tubulin was used as loading control and for normalization. Microscopy revealed PLCz in the acrosomal and post-acrosomal regions, connecting piece, midpiece, and tail. Post-acrosomal localization was the pattern most frequently observed (55%), followed by acrosomal plus post-acrosomal regions (25%). The PLCz labelling was observed on >85% of midpiece and tail regions, independent of Ab used. Flow cytometric evaluation revealed that percentage of live sperm was 47 ± 2%. Similar fluorescence intensity was exhibited for both Ab (M163 and H50) with a wide range of values among stallions [M163, mean 30.7 ± 1.9 × 103 (range, 8.8-82.2 × 103); H50: 25.5 ± 3.2 × 103 (7.3-55.0 × 103)]. The percentage of live sperm within a sample was not associated with Ab MFI. However, when samples were gated for live/dead cells, live sperm exhibited higher (P < 0.001) MFI than dead sperm for M163 (42.6 ± 6.0 v. 30.6 ± 3.9 × 103) and H50 (38.4 ± 4.7 v. 25.6 ± 3.7 × 103). There was a strong and positive correlation between M163 and H50 MFI for total sperm and live sperm (total: r = 0.81, P < 0.001; live: r = 0.71; P < 0.001). In conclusion, 2 anti-PLCz commercial antibodies detected equine PLCz, and the PLCz was localised on the sperm as described. Flow cytometric evaluation showed that stallions have different quantities of PLCz on their sperm, and this may provide a mean to determine if PLCz on stallion sperm is associated with fertility.
A flow cytometric assay of neutrophil degranulation.