INTRACYTOPLASMIC INJECTION OF HUMAN SPERMATOZOA INTO MOUSE OOCYTES - A USEFUL MODEL TO INVESTIGATE THE OOCYTE-ACTIVATING CAPACITY AND THE KARYOTYPE OF HUMAN SPERMATOZOA

When intracytoplasmic sperm injection (ICSI) is performed, it is impor tant to know the capacity of sperm cells to activate the oocytes, alth ough knowledge of their ability to fuse with the oocytes is not vital, Hamster oocytes are not suitable for this purpose because they are ea sily activated by the injection procedure itself. We therefore investi gated whether mouse oocytes could be used to assess the activation pro perties of human spermatozoa. Mouse oocytes were randomized for inject ion with initially motile spermatozoa, medium, heat-treated or salt-ex tracted sperm-matozoa, and the survival and activation rates were exam ined. About half of the mouse oocytes survived the intracytoplasmic in jection of a human sperm cell. Unlike hamster oocytes, the rate of act ivation provoked by the injection procedure itself was acceptably low (20%), resembling in this respect the behaviour of human oocytes. Foll owing the injection of initially motile human spermatozoa, all mouse o ocytes were activated. The injection of heat-treated or salt-extracted human spermatozoa resulted in activation rates of 14 and 15% respecti vely, comparable with the results following sham ICSI. These data supp ort the hypothesis of a sperm-associated oocyte activation factor, In most activated oocytes, the human sperm nucleus decondensed to form a male pronucleus. Cytogenetic analysis at the first metaphase revealed that human sperm chromosomes were able to undergo replication in a het erologous environment. From our data we concluded that human spermatoz oa can be injected successfully into mouse oocytes, resulting in a rea sonable survival rate, and that mouse oocytes provide a useful model f or both the assessment of the sperm-associated oocyte activation facto r and the cytogenetic analysis of human spermatozoa.