Changes in the relative abundance of mRNA transcripts for insulin-like growth factor (IGF-I and IGF-II) ligands and their receptors (IGF-IR/IGF-IIR) in preimplantation bovine embryos derived from different in vitro systems

The aim of this study was to determine the relative abundance of mRNAs for the insulin-like growth factor 1 (IGF-1) and IGF-11 ligands, and for the IG F receptors (IGF-IR and IGF-11R) in in vitro preimplantation bovine embryos from the oocyte to the hatched blastocyst stage using two different cultur e systems: TCM-199 supplemented with oestrous cow serum, or synthetic ovidu ct fluid supplemented with polyvinyl alcohol. Development to the two- to fo ur-cell stage and blastocyst stage was significantly higher (P less than or equal to 0.05) in embryos cultured in TCM supplemented with oestrous cow s erum than in those cultured in synthetic oviduct fluid supplemented with po lyvinyl alcohol (61 and 25% versus 55 and 17%, respectively). A semi-quanti tative RT-PCR assay did not detect IGF-1 transcripts at any stage of preimp lantation bovine development, including the hatched blastocyst stage. in bo th culture systems, IGF-1R, IGF-11 and IGF-11R were expressed throughout pr eimplantation development up to the hatched blastocyst stage in a varying p attern. The expression patterns of IGF-1R, IGF-11 and IGF-11R in embryos ge nerated in the two culture systems were not significantly different, except at the expanded blastocyst stage, at which significantly higher amounts of IGF-11R were observed in the TCM system than in the synthetic oviduct flui d system. These results indicate that transcripts of IGF-1R and IGF-11R fol low the standard pattern in which maternal stores of mRNA in the oocyte are slowly depleted up to the 16-cell stage and then re-established at the ons et of embryonic expression of these genes. The lack of detectable IGF-1 tra nscripts in the bovine embryo indicates a predominantly paracrine mode of a ction. The bovine embryo is capable of producing IGF-11, IGF-11R and IGF-1R in large amounts, particularly after hatching, which may be important for the formation of the filamentous conceptus. Results indicate an autocrine m echanism for IGF-11 and modulation of IGF family expression by culture cond itions.