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 IGF receptors (IGF-IR and IGF-11R) in in vitro preimplantation bovine embryos from the oocyte to the hatched blastocyst stage using two different culture systems: TCM-199 supplemented with oestrous cow serum, or synthetic oviduct fluid supplemented with polyvinyl alcohol. Development to the two- to four-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 serum than in those cultured in synthetic oviduct fluid supplemented with polyvinyl alcohol (61 and 25% versus 55 and 17%, respectively). A semi-quantitative RT-PCR assay did not detect IGF-1 transcripts at any stage of preimplantation bovine development, including the hatched blastocyst stage. in both culture systems, IGF-1R, IGF-11 and IGF-11R were expressed throughout preimplantation development up to the hatched blastocyst stage in a varying pattern. The expression patterns of IGF-1R, IGF-11 and IGF-11R in embryos generated 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 fluid system. These results indicate that transcripts of IGF-1R and IGF-11R follow 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 onset of embryonic expression of these genes. The lack of detectable IGF-1 transcripts in the bovine embryo indicates a predominantly paracrine mode of action. 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 mechanism for IGF-11 and modulation of IGF family expression by culture conditions.