Tissue and development specific regulation of a complex family of rat insulin-like growth factor I messenger ribonucleic acids.
To obtain information about the functional significance of the structural heterogeneity that has been described for rat insulin-like growth factor I (IGF-I) cDNAs, we hybridized polyadenylated RNAs from rat tissues at different developmental stages with probes specific for two variant 5'-sequences (designated here as type 1 and type 2), with a probe specific for IB type E domain coding sequences and with a probe for E domain sequences common to IA and IB type IGF-I cDNAs. Northern blot analyses revealed that previously reported rat liver IGF-I mRNAs of estimated size 7.5-7.0, 1.9-1.5, and 1.2-0.9 kilobases each are comprised of multiple closely migrating IGF-I mRNA species containing either of two 5'-sequences and either IA or IB type E domain coding sequences. In liver, each of these detected IGF-I mRNA species showed postnatal increases in abundance. The mRNAs detected with the probe for type 2 5'-sequences were detected exclusively in postnatal liver and also showed a different pattern of postnatal increase in abundance than other IGF-I mRNA types. IGF-I mRNAs detected with the probe for IB type E domain coding sequences likewise were highly liver specific and were undetectable or barely detectable in other fetal or adult rat tissues. In contrast, IGF-I mRNAs that hybridized with probes for type 1 5'-sequences or for E domain coding sequences common to IA and IB type IGF-I mRNAs were detected in all fetal and adult rat tissues tested. These findings suggest development and tissue specific regulation of the expression of different rat IGF-I mRNA types, and also suggest a possible role of different precursor sequences encoded by the various mRNAs in targeting of IGF-I to a local site of action.
Hoyt
E C
EC
Department of Pediatrics, University of North Carolina School of Medicine, Chapel Hill 27514.
Van Wyk
J J
JJ
Lund
P K
PK
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D004247:DNA / Q000032:analysis / Q000235:genetics; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008099:Liver / Q000502:physiology; D008297:Male; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000235:genetics*
D012333:RNA, Messenger; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D004247:DNA