285 THE EFFICIENCY OF INTRACYTOPLASMIC SPERM INJECTION v. LASER-ASSISTED IN VITRO FERTILIZATION WITH FROZEN SPERM FOR RECOVERY TRANSGENIC C57BL/6 MOUSE STRAINS

Abstract

The progress of molecular genetics generated thousands of new transgenic strains of mice which also requires their economic and safe maintenance in the form of genetic banks. Sperm freezing would be one of the easiest options; however, cryosensitivity of sperm in mice strains is prone to variation. In this study, we examined the efficiency of laser-assisted zona drilling in vitro fertilization (ZD-IVF) v. intracytoplasmic sperm injection (ICSI) for attempting to recover two transgenic (UBI-GFP/BL6 and B6;129P2- Hvcn1) and one mutant (C57BL/6J-Tyr^c-2J) lines. The sperm was frozen with 18% raffinose and 3% skim milk (Nakagata 2000 Mamm Genome 11, 572–576). Data of the replicates was analysed by chi-square method. The motility rates after thawing of cryopreserved sperm were 10% for UBI-GFP/BL6, 30% C57BL/6J-Tyr^c-2J and 50% for B6;129P2-Hvcn1 strains. Regular IVF attempts in the UBI-GFP/BL6 and the mutant strain resulted in very few embryos and no pups (data not shown). Following ZD-IVF, the 2-cell stage rates were 7/60 (12%) for UBI-GFP/BL6, 18/60 (30%) for C57BL/6J-Tyr^c-2J, and 34/60 (56%) for B6;129P2- Hvcn1. After ICSI, 66–74% of the oocytes survived the procedure and their development to 2-cells stage were 12/20 (60%) (UBI-GFP/BL6), 25/39 (64%) (C57BL/6J-Tyr^c-2J) and 26/37 (70%) (B6;129P2-Hvcn1). The number of 2-cell stage embryos produced by ICSI was significantly (P < 0.05) increased compared with those produced following ZD-IVF in case of UBI-GFP/BL6 and C57BL/6J-Tyrc-2J strains. The 2-cell stage embryos were transferred into recipients and the newborn rates from ZD-IVF v. ICSI embryos were 0% v. 17% (UBI-GFP/BL6), 28% v. 36% (C57BL/6J-Tyr^c-2J) and 12% v. 12% (B6;129P2- Hvcn1), respectively; none of them were significantly different. In conclusion, when using cryopreserved sperm, the post-thaw motility is an important indicator for the selection of the rederivation method of cryopreserved transgenic mouse strains; while ZD-IVF, an easier method to perform, is suitable for the higher motility samples, ICSI could be strongly recommended for those showing low motility.