74 STUDY OF TRANSGENIC GOATS EXPRESSING HUMAN GRANULOCYTE–MACROPHAGE COLONY-STIMULATING FACTOR IN THE MAMMARY GLAND

Abstract

Somatic cell nuclear transfer (SCNT) is one of the most useful methods for production of transgenic animals. While both adult and fetal fibroblasts have been used in SCNT, adult cells provide the opportunity to use donor cells from an animal with a proven high yield of milk production. In this study, in vitro development and pregnancy rates were compared following the use of transfected fibroblasts that were obtained from adult and fetal tissues. Ear and fetal fibroblasts were collected from Saanen goats and cultured in serum-starvation condition (TCM-199 + 0.5% FBS) until cell confluence. Linearized DNA containing the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) gene that is targeted for expression in the mammary gland by the β-casein promoter (pBC1/hGM-CSF) was transfected into the cells using lipofectamine 2000 (Invitrogen, Inc., Carlsbad, CA, USA). Transfected colonies were selected with G418 for 14 days. Well-separated colonies were isolated and screened for the presence of transgene by PCR and southern blotting. Recipient oocytes were surgically collected by flushing the oviducts of FSH-stimulated goats at 35 h after hCG injection. The zonae pellucidae of the oocytes were partially drilled using a laser system and each somatic cell was individually transferred into the enucleated oocyte. The couplets were electrically fused and activated by ionomycin + 6-DMAP. The reconstructed embryos were cultured in mSOF medium containing 0.8% BSA at 39°C in an atmosphere of 5% CO₂, 5% O₂, 90% N₂ for 12 to 15 h. Nuclear transfer embryos (2- to 4-cell stages) were surgically transferred into the oviducts of recipients that were in either natural or induced estrus. Pregnancy was diagnosed by progesterone assay and ultrasound on Days 21, 42, and 60 of pregnancy. The type of donor cells, ear or fetal fibroblasts, affected neither the fusion rate (54/65, 83.1% vs. 89/116, 76.7%, respectively) nor the cleavage rate (19/54, 35.2% vs. 37/89, 41.6%, respectively). A total of 55 embryos derived from ear fibroblasts and 84 embryos derived from fetal fibroblasts were transferred into 9 and 14 recipients, respectively. No pregnancy was observed in recipients that received NT embryos derived from ear fibroblasts (0/9); however, 5 (2 in natural estrus and 3 in induced estrus; 35.7%), 3 (1 in natural and 2 in induced estrus; 21.4%), and 2 (2 in induced estrus; 14.3%) of 14 recipients that received NT embryos derived from fetal fibroblasts were confirmed pregnant on Days 21, 42, and 60, respectively. These results imply that the type of donor cells for nuclear transfer may be directly correlated with the success rate. More studies will be needed to examine factors affecting production of transgenic goats and to improve results obtained using adult donor cells.