Differential expression of fibroblast growth factor receptors during rat lens morphogenesis and growth.

PURPOSE: Fibroblast growth factors (FGF) play important roles in the developmental biology of the lens. Recently, it was shown that the expression of one of the FGF receptors, FGFR1 (flg; fibroblast growth factor receptor 1), was closely associated with the onset of lens fiber differentiation. In this study, the expression patterns of three other members of the FGF receptor family were analyzed and compared. METHODS: The expression patterns of FGFR2 (bek and keratinocyte growth factor receptor [KGFR] variants) and FGFR3 were analyzed by in situ hybridization during embryonic and postnatal lens development. RESULTS: In the ocular primordia, both FGFR2 variants were detected on embryonic day 12 (E12) and FGFR3 was detected on E14. From E16 to E20, distinct spatial expression patterns became evident within the lens; FGFR3 showed an anteroposterior increase in expression, with strongest expression in the outer cortical fibers. In contrast, bek showed uniform expression throughout the lens epithelium (including the central and germinative zones) and the transitional zone, with a subsequent decline in maturing fibers. The KGFR variant of FGFR2 showed strongest expression in the early fibers of the transitional zone; its expression in the epithelium was weaker in the germinative zone of embryonic and neonatal rats. There was an age-related decline in expression of FGFRs after birth-an effect that was more marked for FGFR3 than for the FGFR2 variants. CONCLUSIONS: Combined with those in a previous study, these results indicate that the FGFR1, bek, KGFR, and FGFR3 genes exhibit different, yet overlapping, patterns of expression throughout lens development and differentiation. The distinct spatiotemporal patterns of expression of FGF receptors may play an important role in regulating anteroposterior patterns of lens cell behavior.