A homologue of pancreatic trypsin is localized in the acrosome of mammalian sperm and is released during acrosome reaction

We have identified cDNA and genomic clones encoding a homologue of pancreat ic trypsin, termed TESP4, as a candidate protein involved in the sperm pene tration of the egg zona pellucida in mouse. The deduced amino acid sequence indicates that TESP4 is 90% identical to pancreatic trypsin. Analysis of N orthern blotting and reverse transcriptase-polymerase chain reaction reveal s that the mouse TESP4 gene is ubiquitously expressed in all tissues tested , including the pancreas and testis, and the transcript is present in the h aploid stages of male germ cells. Moreover, immunochemical analysis of mous e cauda epididymal sperm using an affinity-purified antibody against bovine pancreatic trypsinogen shows that TESP4 is localized only in the sperm acr osome and is released during the acrosome reaction induced by calcium ionop hore A23187. These findings may open a new point of view regarding the mole cular mechanisms of the sperm/egg interactions, including the sperm penetra tion of the egg zona pellucida.