Rat insulin-like growth factor II gene. A single gene with two promoters expressing a multitranscript family.

We have characterized the single-copy rat gene encoding the protein precursor of insulin-like growth factor II (pre-pro-rIGF-II) that is located downstream from and in the same transcriptional orientation as the homologous insulin II gene (5'-insulin-IGF-II-3'). This gene consists of at least three coding exons and utilizes two promoters that generate alternate 5' non-coding exons. Multiple transcripts from both promoters appear primarily in fetal or neonatal tissues (in all of the developmental stages and tissues that we have examined), but they are extremely rare or undetectable in adult tissues, with the exception of the brain and the spinal cord. These transcripts, which exhibit characteristic developmental profiles in various tissues, differ both in the presence of one of the alternate 5' non-coding exons and in the length of their fourth exon. The possible occurrence of differential splicing or differential polyadenylation (or both) in this region is discussed.