EMBRYONIC STEM-CELLS EXPRESS GROWTH-HORMONE RECEPTORS - REGULATION BYRETINOIC ACID

Embryonic and fetal gro-th are generally considered to be independent of pituitary GH. However, it has been demonstrated recently that 18-da y-old rat embryos and rat fetuses express GH receptors, suggesting tha t GH could play a role in early development. The aim of the present in vestigation was to determine whether preimplantation embryos also expr ess 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, revers e transcription/polymerase chain reaction assays and immunohistochemis try for the detection of GH receptors. Northern blot analysis of ES ce lls using a probe corresponding to the extracellular domain of the GH receptor demonstrated the presence of two transcripts (1.2 and 4.5 kil obases). The RNAse-protection solution-hybridization assay revealed th at ES cells express approximately one sixth of the GH-receptor messeng er 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 ident ified in ES cells, preimplantation embryos, muscle, liver, and placent a by a reverse transcription/polymerase chain reaction assay. In human s it has previously been shown that exon 3 of the GH-receptor is delet ed in the placenta. However, none of the studied mouse tissues had a d eletion of the GH-receptor mRNA corresponding to exon 3 of the human G H receptor. GH-receptor immunoreactivity was identified on the culture d ES-cells by immunohistochemistry. In conclusion, we have in the pres ent study shown that germline competent ES cells and preimplantation m ouse embryos express the GH receptor transcript and that this transcri ption is increased by retinoic acid in ES cells. Furthermore, the pres ence of GH-receptor immunoreactivity on the ES cells indicates that th e GH-receptor transcript is translated.