PARENT SESSION

(W333) THE EFFECT OF ACROSOME ON ICSI OUTCOME.

Morozumi, Kazuto¹, Yanagimachi, Ryuzo¹, ¹ University of Hawaii Medical School, Honolulu, Hawaii

ABSTRACT- Prior to normal fertilization, the sperm plasma membrane over the acrosome and the contents of the acrosome are shed as a result of the acrosome reaction. The acrosome contents, with a spectrum of hydrolyzing enzymes, never enter the ooplasm. While hamster oocytes injected with acrosome-intact hamster spermatozoa all die, mouse and human oocytes injected with acrosome-intact spermatozoa of their own species do not, culminating in the birth of normal offspring. This prompted us to investigate whether acrosomes of mouse and human spermatozoa are totally harmless to the oocytes. When acrosome-intact hamster sperm heads were injected individually into mouse oocytes, all the oocytes deformed extensively within 4 hr. This was due to an abnormal assembly of microtubules. None of the oocytes cleaved. Mouse oocytes did not deform when they were injected with a single hamster sperm head without acrosome. While mouse oocytes each injected with a single acrosome-intact mouse sperm head survived and developed into live offspring, those receiving more than 4 sperm heads deformed within 7 hr without further development. Mouse oocytes injected with 0.07 ng trypsin per oocyte deformed extensively within 5 min, while those injected with heated trypsin (100 °, 2 min) did not. Injection of more than 4 acrosome-intact human spermatozoa into mouse oocytes resulted in the appearance of "vacuole-like"structures within the ooplasm without deformation of oocytes. Thus, three species studied here can be arranged in the following order with respect to the "toxicity" of acrosome on the (mouse) oocyte: hamster >> mouse > human. This order correlates to the volume of the acrosome. For the species with large acrosomes, removal of acrosomes prior to ICSI is recommended. Although human spermatozoa do not need to be freed from acrosomes prior to ICSI, removal of the acrosome is theoretically preferable.

KEY WORDS: acrosome enzyme, hamster sperm, fertilization, ICSI