Actin distribution and tyrosine phosphorylation in sex-sorted bull spermatozoa

Sexing semen has reached a high commercial level in bovine, even if fertility after sorting is still variable because of stresses due to the process. This study was aimed at evaluating actin rearrangement and protein tyrosine phosphorylation (TP) in sexed spermatozoa, as compared to freshly ejaculated, capacitated and acrosome reacted sperm, in order to determine possible capacitation-like changes. As for TP, sexed spermatozoa showed two main patterns: cells positive in both acrosome and equatorial subsegment (EQSS) (49.3 ± 10.3%, mean ± SEM, five replicates) and cells with acrosome immunoreactivity (43.6 ± 11%). The remaining population was equally divided into EQSS positive and negative spermatozoa. This condition is in-between the fresh (77.2 ± 12.6% acrosome positive) and capacitated (84.9 ± 7.4% acrosome and EQSS positive) spermatozoa pattern distribution. As for actin, three different patterns (F, C and R, typical of fresh, capacitated and acrosome reacted cells, respectively) were observed. In fresh cells, F 92.7 ± 0.4%, C 5 ± 0.4%, R 2.3 ± 0.8%; in capacitated cells, F 47.7 ± 2.4%; C 44.4 ± 2.1%; R 7.9 ± 0.6%; in acrosome reacted cells, F 5.2 ± 0.5, C 55.8 ± 5.8%, R 39 ± 5.5%. Sex-sorting determined a capacitation-like distribution, with an increase of C pattern: F 28 ± 9%, C 67 ± 11%, R 5 ± 2%. In conclusion, sex sorting in bull sperm cells seems to induce capacitation-like changes that could be responsible for reducing semen quality; other studies on possible functional modifications could be useful to improve sexed semen performance.