Expression of a growth hormone-responsive exon of the ovine insulin-like growth factor-I gene.
The sheep insulin-like growth factor-I (IGF-I) gene encodes mRNAs containing three different 5'-untranslated sequences as a consequence of alternate splicing of leader exons. Using a combination of RNase protection and primer extension assays, we have mapped the transcriptional start sites of one of the leader exons, exon 1A. Transcription from exon 1A appeared to initiate from multiple points within a 20 bp region situated about 60 bp upstream of the exon 1A splice site. The presence of this transcript in the liver of animals treated with GH was enhanced five- to tenfold and contributed to about 95% of the total hepatic increase in IGF-I mRNA. This exon is generally expressed in a number of tissues immediately after birth; by about 4 weeks postpartum, however, expression is confined to liver. The regulation of hepatic and non-hepatic IGF-I synthesis by GH may involve different mechanisms.
Saunders
J C
JC
Institute of Animal Physiology & Genetics Research, Babraham, Cambridge.
Dickson
M C
MC
Pell
J M
JM
Gilmour
R S
RS
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA; D005091:Exons; D005786:Gene Expression Regulation; D013006:Growth Hormone / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D015183:Restriction Mapping; D012756:Sheep; D014158:Transcription, Genetic
D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D004247:DNA