Rescue of sperm protein tyrosine phosphorylation and fertility in spermatozoa from Cst8−/− mice after incubation in dbcAMP and IBMX. A) Western blot analysis of protein tyrosine phosphorylation in Cst8+/+ and Cst8−/− spermatozoa after increasing periods of time in capacitation buffer and in the presence of dbcAMP and IBMX or the vehicle DMSO. Blots were stripped and reprobed with anti-tubulin antibody to verify equal loading of the gel. Blots are representative of those from three different experiments. B) Percentage of COCs fertilized after 3 h of incubation with Cst8+/+ and Cst8−/− spermatozoa that were untreated, incubated with dbcAMP, or incubated with dbcAMP and IBMX before addition to the oocytes. Values represent the mean ± SEM (n = 10 experiments; a vs. b, P ≤ 0.05; c vs. a, P ≤ 0.001; c vs. b, P ≤ 0.05; c vs. ab, P ≤ 0.01; bc vs. a, P ≤ 0.01).