Expression of exon 3-retaining and -deleted human growth hormone receptor messenger ribonucleic acid isoforms during development.

Recent investigations have suggested that human GH (hGH) and its receptor may have specific functions during human fetal life. To improve our understanding of the mechanisms of hGH action during gestation, we characterized the ontogenic appearance of hGH receptor messenger ribonucleic acid (mRNA) in multiple human fetal and postnatal tissues. Using RT-PCR assays, followed by Southern hybridization to confirm the specificity of the amplified fragments, we scanned the entire coding region of the hGH receptor mRNA. Transcription of the hGH receptor gene was observed in all fetal tissues studied (liver, kidney, skin, muscle, lung, adrenal, spleen, intestine, central nervous system, pancreas, and placental villi) from the earliest stage that could be examined [7-14.8 weeks fetal age (FA)]. Furthermore, we identified only 2 isoforms of the hGH receptor mRNA-coding region: exon 3 can be retained or deleted. Surprisingly, we found individual-specific, not tissue-specific, expression patterns of these two transcripts when we examined multiple tissues (n = 2-6) from 15 individuals (11.5-33 weeks FA); this individual-specific pattern of expression is maintained in cultured dermal fibroblasts for at least 12 generations (n = 2; 16 and 20 weeks FA). In addition, a cross-sectional study of 78 individuals (9 weeks FA to 43 yr postnatal age) showed that the exon 3-deleted transcript is predominantly expressed in tissues from fetuses of 9-20 weeks FA (P < 0.002). Finally, we showed that the absence of exon 3 from the mRNA is not due to genomic deletion of exon 3 by amplifying exon 3 from genomic DNA of 3 fetuses (13.3-19 weeks FA) expressing only the exon 3-deleted mRNA transcript. We conclude that 1) transcription of the hGH receptor gene occurs in multiple tissues as early as the first trimester of human fetal life; 2) the exon 3-retaining and -deleted transcripts are the only two isoforms of the hGH receptor mRNA-coding region during gestation; and 3) the pattern of expression of these transcripts is individual specific and may be developmentally regulated.