Autoradiographic study of mouse spermatozoan arginine-rich nuclear protein in fertilization

General labeling of ripe mouse spermatozoa was obtained two weeks after six injections of L-arginine-5-3H monohydrochloride, administered within two days. Besides tail labeling a very intensive nuclear labeling was obtained. It is presumed that this nuclear labeling represents almost exclusively tritiated arginine incorporation into basic nuclear protein. Mouse oocytes were fertilized in vitro with such labeled spermatozoa. It was found that the nuclear label is lost very early during male pronucleus formation, probably concomitantly with sperm chromatin decondensation. This might indicate total loss of the basic spermatozoal nuclear protein before male genome activation.