Tissue-specific transcription start site usage in the leader exons of the rat insulin-like growth factor-I gene: Evidence for differential regulation in the developing kidney

Joshua Shemer, Martin L Adamo, Charles T. Roberts, Derek Leroith

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

The production of insulin-like growth factor-I (IGF-I) in extrahepatic tissues supports both autocrine and paracrine functions and is regulated differently from that in liver, which supports endocrine function. In rat liver, transcription initiation primarily occurs at four distinct, widely separated sites in exon 1 of the IGF-I gene, whereas in exon 2, transcription initiation occurs at a cluster of sites. To understand the molecular basis for tissue-specific regulation of IGF-I gene expression, we have mapped transcription start site usage in the following extrahepatic tissues: testes, lung, kidney, heart, brain, muscle, and stomach, with liver serving as a control. In adult rats, kidney and brain exhibited a pattern of exon 1 transcription similar to that seen in liver, i.e. roughly equivalent use of start sites 2 and 3. In contrast, testes and lung preferentially used start site 3, while stomach, heart, and muscle predominately used start site 3. Start sites 1 and 4 were used in all tissues at extremely low levels. In those tissues studied in which exon 2 transcripts are expressed (testes, lung, stomach, and kidney), the pattern of exon 2 transcription initiation was identical to that in adult rat liver. During postnatal development, the use of all transcription start sites in exons 1 and 2 was coordinate in lung and stomach. Selection of transcription start sites in the kidney, on the other hand, was subject to regulation during postnatal development. Specifically, within exon 1, start site 3 was expressed constitutively throughout peri-and postnatal development. In contrast, the usage of start site 2 was not detected at late fetal or early postnatal stages, but appeared and rapidly increased only at the stage of weaning. Exon 2 transcripts in kidney also did not appear until the postnatal period. These data suggest tissue-specific and developmentally regulated transcription factors regulating IGF-I promoter activity or, alternatively, tissue-specific and developmental stage-dependent differences in the stability of IGF-I mRNAs resulting from the use of different transcription start sites. These different mRNAs may be of significance in the differential regulation of IGF-I production for autocrine or paracrine function.

Original languageEnglish (US)
Pages (from-to)2793-2799
Number of pages7
JournalEndocrinology
Volume131
Issue number6
StatePublished - Dec 1992
Externally publishedYes

Fingerprint

Transcription Initiation Site
Insulin-Like Growth Factor I
Exons
Kidney
Genes
Stomach
Liver
Testis
Lung
Myocardium
Messenger RNA
Brain
Weaning
Transcription Factors
Gene Expression

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

Cite this

Tissue-specific transcription start site usage in the leader exons of the rat insulin-like growth factor-I gene : Evidence for differential regulation in the developing kidney. / Shemer, Joshua; Adamo, Martin L; Roberts, Charles T.; Leroith, Derek.

In: Endocrinology, Vol. 131, No. 6, 12.1992, p. 2793-2799.

Research output: Contribution to journalArticle

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abstract = "The production of insulin-like growth factor-I (IGF-I) in extrahepatic tissues supports both autocrine and paracrine functions and is regulated differently from that in liver, which supports endocrine function. In rat liver, transcription initiation primarily occurs at four distinct, widely separated sites in exon 1 of the IGF-I gene, whereas in exon 2, transcription initiation occurs at a cluster of sites. To understand the molecular basis for tissue-specific regulation of IGF-I gene expression, we have mapped transcription start site usage in the following extrahepatic tissues: testes, lung, kidney, heart, brain, muscle, and stomach, with liver serving as a control. In adult rats, kidney and brain exhibited a pattern of exon 1 transcription similar to that seen in liver, i.e. roughly equivalent use of start sites 2 and 3. In contrast, testes and lung preferentially used start site 3, while stomach, heart, and muscle predominately used start site 3. Start sites 1 and 4 were used in all tissues at extremely low levels. In those tissues studied in which exon 2 transcripts are expressed (testes, lung, stomach, and kidney), the pattern of exon 2 transcription initiation was identical to that in adult rat liver. During postnatal development, the use of all transcription start sites in exons 1 and 2 was coordinate in lung and stomach. Selection of transcription start sites in the kidney, on the other hand, was subject to regulation during postnatal development. Specifically, within exon 1, start site 3 was expressed constitutively throughout peri-and postnatal development. In contrast, the usage of start site 2 was not detected at late fetal or early postnatal stages, but appeared and rapidly increased only at the stage of weaning. Exon 2 transcripts in kidney also did not appear until the postnatal period. These data suggest tissue-specific and developmentally regulated transcription factors regulating IGF-I promoter activity or, alternatively, tissue-specific and developmental stage-dependent differences in the stability of IGF-I mRNAs resulting from the use of different transcription start sites. These different mRNAs may be of significance in the differential regulation of IGF-I production for autocrine or paracrine function.",
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