• FGF-4 (Fibroblast Growth Factor-4), also known as FGF-K and K-FGF, is a secreted angiogenic factor that is mitogenic for fibroblasts and endothelial cells. During development, it is required for maintenance of the trophectoderm and primitive endoderm, and it cooperates with FGF-8 in the apical ectodermal ridge. FGF-4 promotes embryonic stem cell proliferation and may also aid stem cell differentiation. 
• In vitro, FGF-4 is mitogenic for fibroblasts and endothelial cells. FGF-4 has been shown to be a potent angiogenesis promoter in vivo. FGF-4 has potent transforming potential apparently through an autocrine mechanism of action. FGF-4 plays a key role in limb development and has been identified as the molecular mediator of the activities of the apical ectodermal ridge that is required for directing the outgrowth and patterning of vertebrate limbs.

Gene targeting strategy for B-hFGF4 mice. The exons 1-3 of mouse Fgf4 gene that encode the whole molecule (ATG to STOP codon), including 3’UTR, promoter and 5’UTR region were replaced by human counterparts in B-hFGF4 mice. The human FGF4 expression is driven by human FGF4 promoter, and mouse Fgf4 gene transcription and translation will be disrupted. 

Western blot analysis of FGF4 protein expression in homozygous B-hFGF4 mice. Various tissue lysates were collected from wild-type C57BL/6 mice (+/+)  and homozygous B-hFGF4 mice (H/H), and then analyzed by western blot with anti-FGF4 antibody(abcam, ab106355). 40 μg total proteins were loaded for western blotting analysis. hFGF4 was detected in liver, lung, brain, small intestine and colon(red arrow). 

Strain specific analysis of FGF4 mRNA expression in wild-type C57BL/6 mice and B-hFGF4 mice by RT-PCR. brain RNA were isolated from wild-type C57BL/6 mice (+/+) and homozygous B-hFGF4 mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse or human FGF4 primers. Mouse Fgf4 mRNA were detectable only in wild-type C57BL/6 mice. Human FGF4 mRNA was detectable only in homozygous B-hFGF4 mice but not in wild-type mice.