Phenotypic analysis of mouse spermatozoa lacking Prss55. A. IVF rates (percentage of two-cell stage eggs) in cumulus-intact oocytes using Prss55 heterozygous (Het) and homozygous (KO) spermatozoa. Average IVF rates of Het and KO spermatozoa were 97.6 ± 0.1 and 86.9 ± 12.9%, respectively. N.s., no significance (P > 0.05). Error bars, mean ± SD. B. IVF rates (percentage of two-cell stage eggs) in cumulus-free oocytes using spermatozoa from Het and KO mice. Average IVF rates of Het and KO spermatozoa were 94.6 ± 2.2 and 30.2 ± 5.2%, respectively. **P < 0.01. Error bars, mean ± SD. C. IVF rates (percentage of two pronuclei [2PN] eggs) in ZP-free oocytes using spermatozoa from Het and KO mice. Average IVF rates of Het and KO spermatozoa were 100 and 94.7 ± 7.4%, respectively. N.s., no significance (P > 0.05). Error bars, mean ± SD. D. Sperm–ZP-binding assay. Spermatozoa from Het and KO mice were used to inseminate cumulus-free oocytes. Scale bars, 50 μm. E. Average numbers of ZP-binding spermatozoa per total number of eggs in Het and KO male mice were 35.2 ± 4.6 and 1.2 ± 0.6, respectively. **P < 0.01. Error bars, mean ± SD. F. Detection of ADAM3 and PRSS55 by immunoblotting. EMMPRIN was used as a control. Testis, whole testis; sperm, cauda epididymal spermatozoa; Het, heterozygous; KO, Prss55 homozygous KO. Black arrowheads, molecular weights (kDa). G. Detection of ADAM2, PRSS37, and tACE by immunoblotting. EMMPRIN shown in panel E was used as a control. Testis, whole testis; sperm, cauda epididymal spermatozoa; Het, heterozygous; KO, Prss55 homozygous KO. Black arrowheads, molecular weights (kDa).