Understanding the behavior of transgenes introduced into oocyte or embryos is essential for evaluating the methodologies for transgenic animal production. To date, many studies have reported the production of transgenic pig embryos with, however, low efficiency in environment of blastocyst production. The aim of present study was to determine the expression and duration of transgene transferred by intracytoplasmic sperm injection-mediated gene transfer (ICSI-MGT). Embryos obtained from the ICSI-MGT procedure were analysed for the expression of GFP and then for the transmission of the transgene. Briefly, fresh spermatozoa were bound to exogenous DNA after treatment by Triton X-100 and Lipofectin. When ICSI-MGT was performed using sperm heads with tails removed, the yield of blastocyst (25.3%), treated with Lipofectin (18.8%) and Triton X-100 (19.2%) were observed. Treatments of Lipofectin or Triton X-100 did not further improve the rates of blastocysts. Moreover, the apoptosis rates of embryos were obtained from the control and LIpofectin groups (8.7%, 9.7%, respectively), but were significantly higher in the Triton X-100 group (13.0%). Our results demonstrated that ICSI-MGT caused minimal damage to oocytes that could develop to full term. Moreover, the embryos derived by ICSI-MGT have shown prolonged exogenous DNA expression during preimplantation stage in vivo. However, more efforts will be required to improve the procedures of both sperm treatments cause of high frequency of mosaicisms.

The possibility of producing transgenic embryos expressing the green fluorescence protein (GFP) gene have been evaluated after transfer of exogenous gene into the porcine zygote cytoplasm using the intracytoplasm sperm injection (ICSI) as gene delivery method. For DNA binding to sperm heads, 0.05% Triton X-100 or Lipofectin was used. After injection of the sperm bound to DNA by means of Lipofectin or Triton X-100 triturate, the blastocyst formation rates on day 6 were not significantly different from that of ICSI only group (18.8, 19.2 and 25.3%). In terms of GFP expression, more embryos were in GFP form in Triton X-100 group than in Lipofectin group (40.6 vs 36.4%), while percentage of non-mosaic embryos expressing the GFP gene in all blastomere was higher (P<0.05) in Lipofectin group than in Triton X-100 group (4.2 vs 0.9%). ICSI embryos derived from sperm treated with Lipofectin/DNA complex was transferred into 3 recipients and were collected by uterine flushing on days 5, 7 and 15 after embryo transfer, and then GFP expression was observed by a fluorescence microscopy. Over 26% of the collected embryos were normally expressed GFP gene. These results suggest that foreign gene transfer method with DNA bound sperm caused minimal damage to structure of oocytes that can result to full development of porcine embryos. This was confirmed in this study when the embryos that were transferred after ISCI of DNA bound sperm had a normal development and gene expression until preimplantation.

본 연구에서는 retrovirus를 이용한 유전자 전이에 있어서 대두되는 큰 문제점의 하나인 외래 유전자의 지속적인 발현으로 인한 개체의 생리적인 손상을 최소화하기 위하여 tetracycline계 물질의 공급 여부에 따라서 발현을 유도적으로 조절할 수 있는 one vector 형태의 Tet-On system을 구축하고자 하였다. 또한 WPRE 서열을 이 vector 상에 도입하여 유도적 조건에서 외래 유전자의 발현이 보다 강하게 일어날 수 있는 효율적인 retrovirus vector system을 확립하고자 하였다. 구축한 각각의 vector system에서 fluorometry와 western blotting을 이용하여 GFP 유전자의 발현 정도를 비교 측정한 결과, RevTRE-EGFP-WPRE-RSVp-rtTA2SM2 virus를 이용하여 유전자를 전이시킨 표적세포에서 GFP의 절대적인 발현량이 가장 큰 것으로 나타났고, 유전자 발현의 turn on/off에 의한 유도율은 RevTRE-EGFP-RSVp-rtTA2SM2-WPRE virus의 경우에서 8∼21배로 가장 높은 것으로 나타났다. 이상의 결과에서 외래 유전자의 발현을 효율적으로 조절할 수 있는 vector system은 WPRE가 rtTA2SM2 서열의 3에 위치한 형태로, 이 system을 이용하여 생산한 고감염가의 virus는 유전자 치료나 형질전환 동물의 생산에 있어서 요구되는 외래 유전자의 발현을 효율적으로 조절할 수 있는 수단이 될 것이다.

본 실험에서는 외래 유전자의 효율적인 발현을 위하여 GFP 표지유전자를 이용하여 여러 종류의 promoter를 검정하였다. 또한, retrovirus vector에 WPRE 서열을 도입함으로써 GFP 유전자의 발현 증가 여부를 확인하였다. 모든 표적 세포에 있어서 UbC와 β-actin promoter에 비해 RSV와 CMV promoter 통제하의 GFP의 발현이 더 강하게 나타났으며, 특히 CEF 세포에서는 RSV promoter가 가장 우수한 것으로 확인되었다. WPRE의 도입으로 인한 발현율의 증가는 CEF를 제외한 세포주에서 promoter의 종류에 관계없이 확인되었다. 이상의 결과로 각 세포주는 promoter에 따라 발현 양상이 약간의 차이를 보이고 있으나 RSV와 CMV promoter에서 유전자의 발현이 보다 효율적이며, WPRE 서열이 도입된 경우에 HeLa와 PFF 세포에서 발현이 현저히 증가하는 것을 확인할 수 있었다. 이러한 연구 결과는 효율적인 유전자의 발현 체계를 확립하는데 기여함으로써 더 나아가 유전자 치료나 형질전환 동물생산에 적극적으로 활용되어질 수 있을 것이다.

The efficiency of transgenic livestock animal production may be improved by early selection of transgenci preimplantation embryos. To examine the possibility of GFP gene as a non-invasive marker for the early screening of transgenic embryo, the GFP gene was microinjected into rabbit zygotes and the later stages of preimplantation embryos were examined for the expression of GFP. The presence of injected DNA was detected by PCR analysis and the expression of GFP was detected by observing green fluorescence in embryos under a fluorescent microscope. Out of 108 GFP gene-injected rabbit zygotes, seventy three(67.6%) were fluorescence-positive. When 11 fluroresecence-positive blastocysts were analyzed for the presence of GFP gene by PCR, 6(54.5%) were positive, and all of the 8 flrouescence-negative blastocysts were also negative by PCR. The results indicate that the screening of transgene in rabbit embryos by PCR analysis and GFP detection could be a promising method for the preselection of transgenic embryos.