Expression of the chicken cysteine-rich fibroblast growth factor receptor (CFR) during embryogenesis and retina...

The expression of the chicken cysteine-rich fibroblast growth factor receptor (CFR) during organogenesis and specifically during retina formation was studied by Northern blotting and a sensitive in situ hybridization. At days 2 and 4 of embryonic development (E2 and E4), CFR mRNA was present in a wide variety of developing organs; it was abundantly expressed in nervous structures, particularly in the retina. The levels of CFR transcripts were high during the proliferation and the subsequent differentiation phases of retinal neurogenesis, reached a maximum around E11 during the onset of the major period of retinal cell death, and then declined progressively. CFR mRNA was not detected at late stages when the final arrangement of retinal cell layers has been established. In prolonged primary cell cultures of chicken embryo retina, CFR expression showed a similar down-regulation to that seen with increasing age in vivo. It was up-regulated either directly or indirectly by its ligands. The CFR expression pattern in the developing retina was complementary to that of two other fibroblast growth factor (FGF) receptors, namely FGF-R1 and FGF-R2. In regard to a progressive increase in the expression of their ligands during retinal development, we suggest that CFR may have a role distinct from that of the tyrosine kinase FGF receptors during retinogenesis. Finally, the comparison of CFR expression with those of the other high affinity receptors indicates a regulation of the FGF function at the receptor level during neural retina development.