301 INTRACYTOPLASMIC SPERM INJECTION (ICSI) MEDIATED GENE TRANSFER ASSISTED BY ACTIVATION WITH A DOUBLE EXPOSURE TO IONOMYCIN AND 6-DIMETHYLAMINOPURINE OR DEHYDROLEUCODINE

Abstract

ICSI-mediated gene transfer is a powerful technique used to produce transgenic mice and pigs. However, this method of transgenesis has not been applied in bovine due to low embryo development, which is presumed to be a consequence of a failure in sperm factor delivery after ICSI in this species. To bypass this problem, we assisted ICSI with chemical activation, employing two Ionomycin (Io) exposures and 6-Dimethylaminopurine (DMAP) or a novel drug, Dehydroleucodine (DhL). Cumulus–oocyte complexes were aspirated from ovaries obtained from a local slaughterhouse and in vitro matured in bicarbonate-buffered TCM-199 containing 10% FBS, 10 μg mL^–1 FSH, 0.3 mm sodium pyruvate, 100 μm cysteamine and 10 UI mL^–1 penicillin. IVM conditions were 6% CO₂ in humidified air at 39°C for 24 h. MII oocytes were selected and used immediately for ICSI. Sperm samples were frozen/thawed by standard procedures. Coincubation of spermatozoa with DNA construction (pCX-EGFP) was carried out in Na citrate 2.8%, with 0.5 μg plasmid million^–1 spermatozoa for 5 min at 0°C. Then, spermatozoa were used for ICSI. Injected oocytes were activated in 5 μm Io for 4 min and placed in TCM-199 for 3 h to allow second polar body emission. Afterwards, some of the oocytes were subjected to a second exposure of Io. Oocytes exposed once or twice to Io were then incubated with 2 mm DMAP (groups Io-DMAP and 2Io-DMAP) or 5 mm DhL (groups Io-DhL and 2Io-DhL) for 3 h. Control groups (Io and 2Io) were not treated with DMAP or DhL. Embryos were cultured in the IVM droplets. EGFP expression was daily evaluated in fluorescence microscope under blue light (488 nm). Significant differences between groups were evaluated by Fisher test (Table 1). DhL chemical activation improved neither development nor transgenesis rates. The double Io exposure significantly improved embryo development. The second exposure to Io previous chemical activation with DMAP resulted in an increase in the percentage of EGFP-expressing embryos. Our results indicate that activation with double Io-DMAP could be considered an alternative assistance for ICSI mediated gene transfer in bovine.

Table 1.  Effect of activation assisting transgenic ICSI on development and expression of bovine embryos