• Background: FGF23 (Fibroblast Growth Factor 23) is a hormone-like fibroblast growth factor primarily secreted by osteocytes and osteoblasts. It regulates serum phosphate and active vitamin D levels by binding to the FGFR-Klotho receptor complex. The core physiological functions of FGF23 include maintaining phosphate homeostasis, suppressing renal phosphate reabsorption, inhibiting active vitamin D synthesis, and promoting vitamin D catabolism.
• Application：Efficacy validation for diseases associated with abnormal blood phosphate.
• Targeting strategy: The exons 1-3 of mouse Fgf23 gene that encode the whole molecule were replaced by human counterparts in B-hFGF23 mice. The 3’UTR and 5’UTR region of the mouse gene are retained. The human FGF23 expression is driven by mouse Fgf23 promoter, while mouse Fgf23 gene transcription and translation will be disrupted.
• Validation: Human FGF23 was detectable in homozygous B-hFGF23 mice.
• Mouse Fgf23 mRNA was exclusively detectable in C57BL/6Nifdc. Human FGF23 mRNA was exclusively detectable in homozygous B-hFGF23 mice.

Gene targeting strategy for B-hFGF23 mice. The exons 1-3 of mouse Fgf23 gene that encode the whole molecule were replaced by human counterparts in B-hFGF23 mice. The 3’UTR and 5’UTR region of the mouse gene are retained. The human FGF23 expression is driven by mouse Fgf23 promoter, while mouse Fgf23 gene transcription and translation will be disrupted.

Western blot analysis of FGF23 protein expression in homozygous B-hFGF23 mice. Various tissue lysates were collected from wild-type C57BL/6N mice (+/+) and homozygous B-hFGF23 mice (H/H) (male, 6-week-old), and then analyzed by western blot with anti-FGF23 antibody(Abcam, ab307420). 40 μg total proteins were loaded for western blotting analysis. FGF23 was detectable in kidney, thymus, heart and spleen.

Strain specific analysis of FGF23 mRNA expression in wild-type C57BL/6N and B-hFGF23 mice by RT-PCR. Thymus RNA were isolated from wild-type C57BL/6N (+/+) and homozygous B-hFGF23 mice(H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse and human FGF23 primers. Mouse Fgf23 mRNA was exclusively detectable in C57BL/6N. Human FGF23 mRNA was exclusively detectable in homozygous B-hFGF23 mice.