POSITIVE EFFECT OF PARTIAL ZONA-PELLUCIDA DISSECTION ON THE IN-VITRO FERTILIZING-CAPACITY OF CRYOPRESERVED C57BL 6J TRANSGENIC MOUSE SPERMATOZOA OF LOW MOTILITY/

Although cryopreservation of mouse spermatozoa has recently become ava ilable for use, as yet there are considerable differences in fertiliza tion efficiency of cryopreserved spermatozoa among various mouse strai ns. In this study, oocytes subjected to partial dissection of the zona pellucida (PZD) were inseminated with frozen-thawed C57BL/6J mouse sp ermatozoa. At 30, 60, 120, and 240 min after insemination, the oocytes were washed in human tubal fluid medium and cultured for 36 h. The fe rtilization rates of the PZD oocytes in each group at 6-7 h after inse mination were significantly higher than that of the zona-intact contro l (73-88% vs 12%, respectively) (p < 0.01); but the incidence of polys permy was nevertheless quite low (1.3-2.4%). The development rates of the monospermic oocytes to the morula and early blastocyst stages were in the 87-92% range, with 31-40% of those developing into offspring a fter embryo transfer. When the cryopreserved spermatozoa of C57BL/6J t ransgenic mice were used to fertilize PZD oocytes, the fertilization r ates were as high as (73-76%) those of the PZD oocytes inseminated wit h the cryopreserved C57BL/6J spermatozoa, with 30-31% of the morulae a nd early blastocysts derived from the monospermatic oocytes developing into offspring. These results indicate that PZD of oocytes may provid e an alternative when the fertilizing capacity of mouse spermatozoa ha s been compromised by cryopreservation.