Expression of alternatively spliced bFGF first coding exons and antisense mRNAs during chicken embryogenesis.

We have identified eight different basic fibroblast growth factor (bFGF or FGF-2) transcripts which can be grouped into three classes expressed during chicken embryogenesis and in specific adult organs. Three of them encode the evolutionarily conserved bFGF proteins. Two additional mRNAs are structurally homologous to the previously isolated Xenopus laevis bFGF antisense transcripts. Their expression during embryogenesis and the inversely proportional amounts of sense and antisense transcripts in several adult organs provide further evidence for a possible regulatory role of the antisense transcripts. Unexpectedly, a novel class of three alternatively spliced bFGF transcripts expressed predominantly during embryogenesis was isolated. Alternative splicing of exon 1 of the open reading frame creates a predicted bFGF isoform containing a completely novel amino-terminal domain. This is the first report describing alternative splicing of the coding region of bFGF. Similar levels of alternatively spliced (alt-bFGF) and canonical bFGF transcripts are expressed during embryogenesis, but in adult organs alt-bFGF transcripts are far less abundant, which suggests roles for the predicted novel bFGF isoform during morphogenesis.