Methodological improvement of fluorescein isothiocyanate peanut agglutinin (FITC-PNA) acrosomal integrity staining for frozen-thawed Japanese Black bull spermatozoa

This study aimed to improve the staining of frozen-thawed Japanese Black bull sperm acrosomes with fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA). Spermatozoa were washed, fixed with 1-3% paraformaldehyde (PFA) in suspension for 10, 20, and 30 min, permeabilized with 0-2% Triton X-100 for 5 min, stained with FITC-PNA, and mounted with different antifade agents (0.22 M 1,4-diazabicyclo [2,2,2] octane (DABCO), SlowFade®, and ProLong®) in suspension (In-suspension) or on a smear (On-smear). The spermatozoa were categorized into seven pattern types either immediately or after storage for 24 hr. Experiment 1 showed that 1) the In-suspension method was better than the On-smear method; 2) if spermatozoa were stained using the In-suspension method and examined immediately, the best antifade agent was SlowFade®; 3) if samples were to be stored after staining using the On-smear method, DABCO should be avoided; 4) if spermatozoa were stained using the In-suspension method, storage of the stained samples was not recommended; and 5) if samples were to be stored after staining using the In-suspension method, ProLong® might be the best antifade agent. The results of experiment 2 showed that the concentration of Triton X-100 could be reduced to 0.1 from 1%. The results of experiment 3 showed that the paraformaldehyde concentration used for a 30 min fixation could be reduced from 3 to 2%. It is expected that the improved staining protocol will be useful to determine bull sperm acrosomal integrity.