THE STRUCTURE AND EXPRESSION OF THE FGF RECEPTOR-1 MESSENGER-RNA ISOFORMS IN RAT-TISSUES

In this paper, we describe the structure of rat FGF receptor-1 mRNA isoforms and their expression in a variety of rat tissues. The rat FGFR-1 has the characteristics of FGFR-1 as well as mouse, human and chicken homologs. FGFR-1 mRNA was detectable in all the tissues examined by Northern analysis or polymerase chain reaction, indicating that FGFR-1 mRNA is widely expressed in rat tissues. The rat FGFR-1 mRNA has isoforms in both the extracellular and intracellular regions. The extracellular isoforms which have two or three immunoglobulin-like domains, are expressed almost equally in the tissues except for brain. However, the large form is a major form in the brain. Furthermore, in the brain, half of FGFR-1 mRNAs have the six nucleotides, which encode a potential serine-threonine kinase phosphorylation site in the intracellular juxtamembrane region, deleted. In contrast to the brain, the deletion isoform is a minor form in the other tissues. The tissue-specific expression of the isoforms indicates that they have different physiological functions. Although other isoforms of FGFR-1 mRNA in tumor cell lines have been reported, the isoforms were undetectable in all rat tissues examined, indicating the isoforms are products of abnormal alternative splicing in tumor cell lines.