Embryonic stem cells express growth hormone receptors: regulation by retinoic acid

Embryonic and fetal growth are generally considered to be independent of pituitary GH. However, it has been demonstrated recently that 18-day-old rat embryos and rat fetuses express GH receptors, suggesting that GH could play a role in early development. The aim of the present investigation was to determine whether preimplantation embryos also express GH receptors. Germ line competent mouse embryonic stem (ES) cells and cultured mouse preimplantation embryos were examined with Northern blot analysis, RNAse-protection solution-hybridization assays, reverse transcription/polymerase chain reaction assays and immunohistochemistry for the detection of GH receptors. Northern blot analysis of ES cells using a probe corresponding to the extracellular domain of the GH receptor demonstrated the presence of two transcripts (1.2 and 4.5 kilobases). The RNAse-protection solution-hybridization assay revealed that ES cells express approximately one sixth of the GH-receptor messenger RNA (mRNA) levels expressed in liver from pregnant mice. Treatment of cultured ES cells with retinoic acid (100 nM) for 6 days increased GH-receptor mRNA levels (P < 0.01). GH-receptor mRNA was further identified in ES cells, preimplantation embryos, muscle, liver, and placenta by a reverse transcription/polymerase chain reaction assay. In humans it has previously been shown that exon 3 of the GH-receptor is deleted in the placenta. However, none of the studied mouse tissues had a deletion of the GH-receptor mRNA corresponding to exon 3 of the human GH receptor. GH-receptor immunoreactivity was identified on the cultured ES-cells by immunohistochemistry. In conclusion, we have in the present study shown that germline competent ES cells and preimplantation mouse embryos express the GH receptor transcript and that this transcription is increased by retinoic acid in ES cells. Furthermore, the presence of GH-receptor immunoreactivity on the ES cells indicates that the GH-receptor transcript is translated.