Disease relevance of Fgf9

• The observations provide evidence that targeted, in vivo activation of endogenous FGFR3 inhibits bone growth and demonstrate that signals derived from FGF9-FGFR3 interactions can physiologically block endochondral ossification to produce a phenotype characteristic of the achondroplasia group of human chondrodysplasias [1].
• FGF9 was originally isolated from a culture medium of a human glioma cell line as a growth-promoting factor for glial cells [5] [2].
• Retinoic acid induces gene expression of fibroblast growth factor-9 during induction of neuronal differentiation of mouse embryonal carcinoma P19 cells [2].
• To begin to understand the developmental role of FGF-9/glial activating factor, we have cloned and sequenced the murine FGF-9 cDNA and expressed the protein in mammalian cells and in Escherichia coli [3].
• In PDE2 binding of cGMP to the GAF domain causes an activation of the catalytic activity by a mechanism that apparently is shared even in the adenylyl cyclase of Anabaena, an organism separated from mouse by 2 billion years of evolution [4].

High impact information on Fgf9

• Fgf9 appears to act downstream of Sry to stimulate mesenchymal proliferation, mesonephric cell migration, and Sertoli cell differentiation in the embryonic testis [5].
• Reproductive system phenotypes range from testicular hypoplasia to complete sex reversal, with most Fgf9(-/-) XY reproductive systems appearing grossly female at birth [5].
• Here we report male-to-female sex reversal in mice lacking Fibroblast growth factor 9 (Fgf9), demonstrating a novel role for FGF signaling in testicular embryogenesis [5].
• In mice, loss of function of Fgf4 (refs 13,14), Fgf9 (D. Ornitz, pers. comm.) or Fgf17 (ref. 15) has no effect on limb formation [6].
• However, we demonstrate that cGMP can directly activate PDE5 without phosphorylation in platelet cytosol, most likely via binding to the regulatory GAF domains [7].

Chemical compound and disease context of Fgf9

• Glia-activating factor (GAF) is a novel heparin-binding growth factor purified from the culture supernatant of a human glioma cell line [8].
• Defined induction of phosphoenolpyruvate carboxykinase synthesis in hydrocortisone-treated rat hepatoma cells permitted reliable quantitation of GAF and analysis of the mechanism of cortisol antagonism [9].
• The glucose level after injection of GAF in cortisone treated mice initially showed hyperglycemia, but declined toward hypoglycemia 2 hr after injection, and thereafter returned nearly to the normal range by 4 hr [10].

Biological context of Fgf9

• Fgf9 signaling regulates inner ear morphogenesis through epithelial-mesenchymal interactions [11].
• Fgf9 maps to chromosome 14 near the Ctla6 locus [12].
• Fibroblast growth factor 9 (FGF9) signal has a role in organogenesis of the mammalian testis by controlling migration of mesonephric cells to the XY gonad, but neither it nor the FGF receptors is expressed sex-specifically [13].
• The amino acid sequence of Fgf9 had similarity greater than 92% with chicken, mouse and human Fgf9s, suggesting that Fgf9 is highly conserved among vertebrate classes [14].
• We present evidence that germ cells resident in the XY gonad become dependent on FGF9 signaling between 10.5 dpc and 11.5 dpc, and that FGF9 directly promotes XY gonocyte survival after 11.5 dpc, independently from Sertoli cell differentiation [15].

Anatomical context of Fgf9

• Fgf9(-/-) lungs exhibit reduced mesenchyme and decreased branching of airways, but show significant distal airspace formation and pneumocyte differentiation [16].
• In embryonic lung, Fgf9 is detected in airway epithelium and visceral pleura at E10.5, but is restricted to the pleura by E12 [16].
• Fgf9 null (Fgf9(-/-)) mouse embryos have agenesis of the embryonic cecum, lacking both mesenchymal expansion and an epithelial bud [17].
• In the mouse, Fgf9 and Wnt4 are expressed in gonads of both sexes prior to sex determination [18].
• FGF-9 may also be involved in differentiation of odontoblasts [19].

Associations of Fgf9 with chemical compounds

• Moreover, receptor binding of FGF9 requires heparin in a manner specific to the receptor type [20].
• The amino acid sequence of proteins purified from culture supernatant of the CHO cell line, which was cDNA transfected and selected as a high producer of FGF-9, showed that no peptides were cleaved from the N terminus except the initiation methionine [8].
• Two cysteine residues and other consensus sequences in family members were also well conserved in the FGF-9 sequence [8].
• However, treatment with IFN-gamma in the presence of protein tyrosine phosphatase inhibitor vanadate blocked the decrease in GAF activity [21].
• The C3H/HeJ mice have been used, therefore, as assay animals to establish that peak levels of GAF appear in donor serum about 2 h after an injection of lipopolysaccharide, and it is produced intraperitoneally in C3H/HeJ mice given a mixture of endotoxin and peritoneal exudate cells derived from responder mice [22].

Regulatory relationships of Fgf9

• Recombinant Fgf9 protein inhibits the differentiation response of the mesenchyme to N-Shh, but does not affect proliferation [23].
• In addition, FGF-9 was shown to stimulate enhancer activity and Sox9 expression [24].
• Microphthalmic eyes were evident in transgenic mice expressing FGF-8, FGF-9 and some lines expressing FGF-4 [25].
• Both gain- and loss-of-function of FGF9 regulates Vegfa expression in lung mesenchyme, and VEGF signaling is required for FGF9-mediated blood vessel formation [26].

Other interactions of Fgf9

• The reduction in the amount of mesenchyme in Fgf9(-/-) lungs limits expression of mesenchymal Fgf10 [16].
• Fgf-8 and Fgf-9 mRNAs were present in the oral epithelium of the first branchial arch at E10 and 1 day later expression became more restricted to the area of presumptive dental epithelium and persisted there until the start of epithelial budding [19].
• Loss of Fgf9 leads to XY sex reversal, whereas loss of Wnt4 results in partial testis development in XX gonads [18].
• FGF9 is found to bind with high affinity (kd: 0.25 nM) to FGFR3, for which a specific ligand has not yet been identified [20].
• We identify FGF-9 as a particularly potent Sox9 agonist [24].

Analytical, diagnostic and therapeutic context of Fgf9

• We suggest a model whereby FGF9 signaling from the epithelium and reciprocal FGF10 signaling from the mesenchyme coordinately regulate epithelial airway branching and organ size during lung embryogenesis [16].
• Molecular cloning and expression in gonad of Rana rugosa WT1 and Fgf9 [14].
• FGF9 did not activate MAPK or signal transducer and activator of transcription-1 pathways in the absence or presence of T(3) [27].
• Using gene targeting in mouse embryonic stem (ES) cells, we introduced two loxP sites flanking exon 1 in the Fgf9 allele, which encodes 93 amino acid residues at the N-terminal of FGF9 [28].
• Analysis by whole mount in situ hybridization further reveals distinct expression patterns for Fgf-18, Fgf-20, and by comparison, Fgf-9, in the calvaria, and Fgfs-20 and -9 in the developing limbs, suggestive of their role in proliferation, differentiation and apoptosis [29].

References