Expression of genes for insulin and insulin-like growth factors and receptors in early postimplantation mouse embryos and embryonal carcinoma cells.

The expression of genes for insulin and insulin-like growth factors (IGFs) and their receptors was examined in early postimplantation mouse embryos and differentiating F9 embryonal carcinoma cells using mRNA phenotyping. Messenger RNA phenotyping involves the reverse transcription of RNA followed by amplification of specific target cDNA sequences using the polymerase chain reaction (PCR). The identities of the resulting PCR fragments were confirmed using at least two of the following methods: 1) size determination by agarose gel electrophoresis, 2) the presence of diagnostic restriction sites, 3) hybridization with radiolabeled cDNA probes, 4) sequencing of the PCR fragment. Transcripts for insulin receptors, IGF-I receptors, and IGF-II receptors were detected in RNA samples from day 7.5 to day 9.5 mouse embryos and in F9 cells, although the level of insulin receptor mRNA in F9 cells was very low. Transcripts for both IGF-I and IGF-II ligands were also detectable in the embryo and F9 RNA samples, but transcripts for insulin ligand were undetectable in either set of material. The results suggest that insulin does not act as a paracrine or autocrine growth factor in early postimplantation embryos or F9 cells but that both embryos and F9 cells have the potential to respond to exogenous (e.g., maternal) sources of insulin. Both IGF-I and IGF-II could act as paracrine or autocrine growth factors, and IGF-II is the more abundant growth factor in differentiating F9 cells.