ALTERNATIVE SPLICING AND DIFFERENTIAL TARGETING OF FIBROBLAST GROWTH-FACTOR RECEPTOR-1 IN THE PREGNANT RAT UTERUS

Recent studies suggest that steroid effects on uterine cell proliferat ion may be moderated by polypeptide growth factors. We now provide evi dence that high affinity fibroblast growth factor (FGF) receptors are present temporally and spatially in the pregnant rat uterus (days 4-6) to support the idea that basic FGF action occurs via binding to its hi gh affinity FGF receptor 1 (FGFR1). Reverse transcription-polymerase c hain amplification indicates that both the full-length transcript and an alternatively spliced messenger RNA are present in the uterus. West ern immunoblot analysis confirms that rat uterine membrane proteins co ntain two receptor isotorms, and these receptors bind basic FGF with h igh affinity and specificity. Immunolocalization of FGFR1 revealed rec eptor-positive cells in both the uterine stroma and epithelia on days 4-6 of pregnancy. However, the receptor was differentially localized i n the disparate cell types. The nuclei of stromal cells were positive for FGFR1, whereas epithelial cell nuclei were negative. Together, the se results suggest that FGF signal transduction in uterine stromal cel ls is mediated by activation of FGFR1.