Coordinate developmental regulation of high and low molecular weight mRNAs for rat insulin-like growth factor II.
Insulin-like growth factor II (IGF-II) is a mitogenic polypeptide that is thought to play a role in fetal growth and development. To study the hormonal and developmental regulation of IGF-II gene expression, we have isolated a cDNA clone for rat IGF-II (rIGF-II) from a 12S [1.2-kilobase-pair (kbp)] fraction of mRNA from a rat liver cell line (BRL-3A) that directs the cell-free synthesis of pre-pro-rIGF-II. In the present study, the rIGF-II probe was used to determine the size of IGF-II RNA. Surprisingly, in BRL-3A cells and in neonatal liver, the probe hybridized under stringent conditions 10-20 times more strongly to a larger (4 kbp) RNA than to 1.2-kbp RNA. The 4-kbp RNA is almost exclusively cytoplasmic and is colinear with a 551-base fragment of the rIGF-II cDNA insert containing coding and 3' noncoding regions. The 4-kbp and 1.2-kbp RNA species are regulated coordinately with developmental age, being high in liver from neonatal rats but not detectable in liver from older animals, suggesting that both IGF-II mRNA species arise from a single primary transcript by alternative RNA processing. Although oligodeoxynucleotide hybridization and S1 nuclease protection experiments suggest that the 4-kbp RNA contains an intact protein-coding region, fractions enriched in 4-kbp RNA do not direct the translation of pre-pro-rIGF-II in vitro. This may indicate that the 4-kbp RNA specifies an altered protein product that has not yet been recognized, or alternatively that it contains a normal protein-coding region but requires further RNA processing to be activated for translation.
Graham
D E
DE
Rechler
M M
MM
Brown
A L
AL
Frunzio
R
R
Romanus
J A
JA
Bruni
C B
CB
Whitfield
H J
HJ
Nissley
S P
SP
Seelig
S
S
Berry
S
S
D000818:Animals; D002451:Cell Compartmentation; D002460:Cell Line; D002474:Cell-Free System; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D005786:Gene Expression Regulation; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D008099:Liver / Q000196:embryology / Q000502:physiology; D008970:Molecular Weight; D009693:Nucleic Acid Hybridization; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D013002:Somatomedins / Q000235:genetics*; D014158:Transcription, Genetic
D012333:RNA, Messenger; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II; D004247:DNA