DEVELOPMENTAL EXPRESSION OF FIBROBLAST GROWTH-FACTOR RECEPTOR-1 (CEK-1-FLG) DURING HEART DEVELOPMENT

Previous work in this laboratory has indicated that fibroblast growth factor-2 (FGF-2; bFGF) regulates the initial stages of avian heart dev elopment in paracrine and autocrine fashion (Parlow et al. [1991] Dev. Biol. 146:139-147; Sugi et al. [1993] Dev. Biol. 157:28-37). Because these findings inferred the presence of a functional receptor for fibr oblast growth factor (FGFR), we have immunochemically assessed the app earance of FGFR-1 (cek-1; flg) during development. Using a peptide-gen erated antibody, Western blots of total embryonic proteins revealed th at FGFR-1 was barely detectable at pre-heart stages, followed by seque ntial increases in relative abundance that peaked at stage 24, followe d by a decline at days 7-14. Western blots of proteins from isolated e mbryonic hearts demonstrated a similar developmental pattern, except t hat FGFR-1 expression was not decreased at later stages. The presence of FGFR-1 mRNA was verified by reverse transcription/polymerase chain reaction (RT/PCR) amplification. Immunohistochemical examination revea led punctate deposits of FGFR-1 in the precardiac endoderm at stage 6, followed by detection in the endoderm, foregut, and pre-cardiac splan chnic mesoderm at stage 8 and in the newly formed myocardium at the he art tube stage (9/10). By stage 13, FGFR-1 staining was observed only in the myocardium, a pattern which persisted at least until stage 30 ( day 7), after which only isolated hearts were examined. After stage 30 , staining was diminished in the ventricle, but not in the atrium. Sta ining of cardiac endothelial cells was not observed at any stage. A fu nctional role for FGFR-1 was indicated by experiments in which anti-FG FR-1, but not pre-absorbed antiserum, retarded proliferation and multi layering of cardiogenic cells in an in vitro model of cardiac morphoge nesis. (C) 1995 Wiley-Liss, Inc.