423 PRODUCTION OF CLONED PIGS EXPRESSING APOLIPOPROTEIN E-SPECIFIC SMALL HAIRPIN (shRNA)

Abstract

Apolipoprotein E (apo E) is a known risk factor for developing premature atherosclerosis and Alzheimer’s syndrome. The aim of this study was to create a pig model with reduced apo E levels using RNA interference (RNAi) and somatic cell nuclear transfer (SCNT) technologies. Three synthetic small interfering RNA targeting the porcine apo E mRNA were designed, and the knockdown efficiency was assessed in cultured porcine granulosa cells by real-time PCR. The observed apo E knockdown efficiency ranged from 45 to 82% compared with control cells, indicating the targeted degradation of apoE mRNA.A small hairpin RNA (shRNA) expressing vector was constructed in PRNAT.U6.Neo (Genscript Corp., Piscataway, NJ, USA) based on the most effective apo E RNAi sequence under the control of polymerase III (U6) promoter, and then introduced into fetal porcine fibroblast cells. Clones were selected by neomycin treatment and green fluorescent protein (GFP) expression. SCNT was performed using IVM oocytes collected from prepubertal gilts. Oocyte maturation and activation and embryo culture were performed as previously described (Nascimento et al. 2009 Reprod. Domest. Anim. in press). Embryos were cultured in vitro for 5 to 6 days, briefly exposed to fluorescent light to confirm GFP expression, and then surgically transferred into the uterus of recipient gilts. The recipient gilts were synchronized by daily oral administration of altrenogest (20 mg day^-1; Regu-Mate^®, Intervet, Millsboro, MD, USA) for 12 or 13 days, followed by 1000 IU of eCG injected in the last day of altrenogest treatment and 500 IU of hCG 72 h later. Pregnancy diagnosis was performed by ultrasonography at Day 20 to 25 after embryo transfer, and parturition was induced by injecting PGF2? (10 mg of dinoprost tromethamine; Lutalyse^®, Pfizer Canada Inc., Montreal, QC, Canada) at Day 115 of pregnancy. Rates of cleavage (74.7%) and development to the blastocyst stage (37.2%) were comparable with that of embryos reconstructed with nontransfected cells from the same cell line. A total of 309 embryos were transferred to 5 recipients, of which 3 became pregnant and farrowed. Seven live and 1 stillborn piglets were delivered naturally. The presence of the introduced plasmid and the expression of the GFP transgene tag were confirmed by PCR in placental and umbilical tissues of all the piglets. Six cloned pigs have survived after weaning and exhibit no obvious morphological defects. The status of apo E gene expression is currently under investigation.

Supported by a NSERC Discovery Grant to VB.