Fibroblast growth factor 23 mRNA expression profile in chickens and its response to dietary phosphorus.

In mammals, fibroblast growth factor 23 (FGF23) regulates phosphate homeostasis in kidney by binding α-Klotho, a coreceptor of FGF23. FGF23 mRNA is highly expressed in bone and slightly expressed in liver, and is regulated by dietary phosphorus. Little is known about distribution and regulation of FGF23 mRNA in avian lineage. The expression of FGF23 and its coreceptor α-Klotho in chicken and embryo were investigated by real-time quantitative PCR. The effect of dietary phosphorus on FGF23 expression was measured. 36 laying hens at 25 wk were randomly assigned to three dietary available phosphorus (AP) treatments for 11 days: 0.15% AP (LP), 0.40% AP (MP), and 0.80% AP (HP). We first cloned the full coding sequence of FGF23 by the reverse transcription PCR from chicken liver and calvaria. Bioinformatics analysis indicated that the deduced amino acid sequence was 57-87% identical to FGF23 of other species. In adult chicken FGF23 mRNA was expressed at unexpected higher level in liver than other tissues evaluated, including calvaria, femur, tibia, medullary bone, brain, spleen, duodenum, jejunum, ileum, heart and kidney (P < 0.0001), and α-Klotho was expressed at highest level in kidney. However, in 18-d chicken embryos, FGF23 mRNA level was much higher in tibia than in liver, heart and jejunum (P < 0.0001). Chickens at 2, 25, 50 and 80 wk had higher FGF23 expression in liver than 18-d chicken embryos, whereas chickens at 25 wk had lower FGF23 expression in tibia than 18-d chicken embryos and 2-wk-old chickens. HP diets significantly increased serum inorganic phosphorus level (P < 0.001) and FGF23 expression (P < 0.05) in bone tissue compared with LP diets, however, FGF23 mRNA abundance in liver was not changed significantly (P > 0.05) by dietary phosphorus treatments. In conclusion, FGF23 mRNA expression pattern in chicken was clearly different from that in mammals and dietary phosphorus regulated the expression of FGF23 in a tissue-specific way.