Table 1). The mfat1 gene expression vector-pST200
was consisted of a muscle creatine kinase enhancer
and a cytomegalovirus enhancer with a chicken bactin
promoter. A PGK/neo expression cassette
flanked by the loxP sites was linked to the backbone
as the selection marker (Fig. 1).
Isolation of transgenic cells
Primary fetal fibroblasts, isolated from a 50-day Luxi
cattle fetus by the trypsin enzyme digestion method,
were transfected with the linearized pST200 vector
and selected under G418 (250 lg/ml) for 8–10 days.
Then the G418-resistant colonies were pooled and
used for SCNT.
Oocytes in vitro maturation
Bovine ovaries were collected from a local abattoir, and
the cumulus oocyte complexes (COCs) were aspirated
from follicles (3–8 mm). Oocytes with three layers of
cumulus cells were selected and maturated in the tissue
culture medium M199 supplemented with 10 % (v/v)
fetal bovine serum (FBS) (HyClone, batch number
SH30070.03), 0.5 lg FSH ml-1 (Sioux Biochemicals),
5 lg LH ml-1 (Sioux Biochemicals), and 1 % (v/v)
Penicillin/Streptomycin and cultured for 20 h.
Nuclear transfer
Matured oocytes were enucleated to remove the first
polar body and surrounding cytoplasm. Donor cells were
then transferred into the enucleated oocytes individually.
The reconstructed embryos were fused inmannitol fusion
mediumwith two DC pulses (1.8 kV/cm for 20 ls).And
then, activated by 5 lM ionomycin (Sigma) for 5 min
and incubated with 10 mg cycloheximide ml-1 (Sigma)
in CR1aa medium under 5 % CO2 in air for 5 h. After
activation, the embryos were further cultured in CR1aa
medium supplemented with 0.4 % BSA for 40 h. Then,
selected and subsequently cultured in CR1aa medium
(4 % FBS) on cumulus cell monolayers for 6–7 days.
Embryo transfer and pregnancy diagnosis
All animal procedures followed the Guide for the Care
and Use of Laboratory Animals of the Northwest A&F
University. Qinchuan cattle, used as recipients, were
synchronized by cloprostenol treatment before