Localization of growth hormone receptor/binding protein messenger ribonucleic acid (mRNA) during rat fetal development: relationship to insulin-like growth factor-I mRNA.
Although GH plays a key role in postnatal growth, prenatal growth is thought to be GH independent. However, recent data has shown GH receptor/binding protein (GHR/ BP) to be present in rat fetal tissues as early as fetal stage E12. The aim of the present study was to investigate tissue-specific production of the GHR/ BP messenger RNA (mRNA) and its relationship to locally transcribed insulin-like growth factor-I (IGF-I) mRNA in the fetus. We have used in situ hybridization to localize GHR/ BP and IGF-I mRNAs in 16.5-, 18.5-, and 20.5-day-old rat fetuses. Furthermore, because the two parameters of the IGF-I gene differentially respond to GH stimulation, we have also investigated the presence and localization of promoter-specific IGF-I mRNAs. We found the distribution of IGF-I and GHR/ BP mRNAs to be widespread but distinct during the fetal stages examined. High levels of IGF-I mRNA were found in connective tissues or their precursors, including the dermis, perichondrium, and gut. In contrast, GHR/ BP mRNA exhibited three distinct patterns of distribution. First, GHR/ BP mRNA was found at epithelial sites adjacent to sites of IGF-I transcription. Second, GHR/ BP and IGF-I mRNAs were found to colocalize in some connective tissues, but GHR/ BP mRNA levels in these sites were often lower than at other sites (i.e. epithelial) of GHR/ BP gene transcription. Third, GHR/ BP mRNA was also found in regions remote from IGF-I mRNA, including the nerve ganglia and inner olfactory bulb. Using promoter-specific IGF-I RNA probes, we detected only promoter 1 transcripts in all fetal tissues examined. The only exception occurred in specialized epithelial cells of the cochlea where we detected high levels of both promoter 1- and 2-derived IGF-I transcripts. We have thus demonstrated a distinct distribution of GHR/ BP and IGF-I mRNAs in the developing rat fetus with coordinate expression at some sites. These findings suggest a role of GH or a GH-like peptide, acting both directly and indirectly via IGF-I, in fetal growth and development.[1]References
- Localization of growth hormone receptor/binding protein messenger ribonucleic acid (mRNA) during rat fetal development: relationship to insulin-like growth factor-I mRNA. Edmondson, S.R., Werther, G.A., Russell, A., LeRoith, D., Roberts, C.T., Beck, F. Endocrinology (1995) [Pubmed]
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