The Expression Pattern Of IGF Gene Family In Bovine IVF And SCNT Embryos

A frequently observed abnormity in cloned bovine offspring is the large offspringsyndrome (LOS), which has been regarded as a main factor associated with prenatal andneonatal morbidity. To date, the pathological mechanisms involved in LOS remain largelyunknown now; incomplete reprogramming of somatic cell nucleus by ooplasm has beenconsidered as the main factor lead to LOS in cloned offspring. Accumulating evidences haveshown that insulin-like growth factor (IGF) family are important imprinted genes which arefunctioned as regulators of cell growth, cell differentiation and embryonic development.Abnormal expressions of IGF family genes have been widely observed in various tissues ofSCNT cows undergone LOS, indicting that there may be close relation between LOS andabnormal expressions of IGF family genes. Therefore, elucidating the expression patterns ofIGF family genes in the every developmental stage of SCNT embryos is of great value for ourunderstanding the mechanisms involving in LOS. In the present study, the expression patternsof several developmentally important genes, including IGF-1,IGF-2and IGF-1R wereexamed and compared in every preimplantation developmental stage (from1-cell to blastocyst)between IVF and SCNT embryos. In addition, the location of IGF-1receptor (IGF-1R)protein on bovine oocytes, in every preimplantation developmental stage of vitro fertilization(IVF) and somatic cell nuclear transfer (SCNT) embryos was detected. The following resultshave been obtained:1. The IGF-1R protein could not be observed in GV oocytes, but could be detected in MIIoocytes, cumulus cells in GV stage, and throughout the preimplantation period (from1-cell toblastocyst) in both IVF and SCNT embryos. Moreover, no obvious difference in the timing,location, and intensity of expression of IGF-1R protein was observed between IVF and SCNTembryos;2. The IGF-1did not express in matured oocytes and preimplantation embryos both inIVF and SCNT groups. The expression of IGF-1R and IGF-2was observed in embryosgenerated both via IVF and SCNT throughout the preimplantation stage. No significantdifference (P﹥0.05) in the IGF-1R expression was observed at every developmental stagebetween SCNT and IVF embryos, but the IGF-2expression level in SCNT embryos wassignificantly higher than that in IVF embryos since8-cell stage (P<0.01);3. Supplementation of exogenous IGF-1(100ng/mL) to the culture medium increased the blastocyst rates at day6both in IVF (20.3%vs8.5%, p<0.01) and SCNT group (24.7%vs10.4%, p<0.01), and decreased apoptosis index (2.31±0.48%vs4.87±0.28%for IVF group,and3.91±0.53%vs7.25±0.32%for SCNT group).The results indicated that IVF and SCNT embryos have similar expression patterns of IGFfamily genes, but IGF-2showed higher expression level since embryonic gene activationstage (8-cell stage) compared with their IVF counterparts. In addition, exogenous IGF-1supplementation can improve the in vitro developmental competence of both IVF and SCNT embryos.