In vivo growth hormone gene expression in neonatal rat thymus and bone marrow

The ontogenesis of GH gene expression in the pituitary gland and immune organs of rats was studied by in vitro amplification of GH mRNA using a specific reverse transcription-polymerase chain reaction. Samples were obtained after microsurgery and total RNA extraction of fetal, neonatal and adult rat tissues. Amplification was followed by analysis using Southern blot techniques and hybridization using a specific digoxigenin-labelled GH cDNA probe. The study was started on day 15 of gestation. GH gene expression occurred in the pituitary gland on day 17. GH mRNA was found in the bone marrow and thymus of neonatal rats but not in the spleen or liver. No GH transcripts were detected in the immune organs of fetal or adult rats. The transient GH expression in rat immune organs may indicate a specific function of GH in the development of the immune system during the neonatal period.