Ligand Systems, Receptor Activation, and Biological Effects of the FGF Pathway

The FGF (fibroblast growth factor) pathway is one of the most important growth factor signaling networks in multicellular organisms, spanning embryonic development, tissue homeostasis, metabolic regulation, injury repair, and tumor progression. The research focus of this pathway is not limited to FGF-FGFR binding itself, but rather lies in how ligand subgroups, receptor splice variants, co-receptors, extracellular matrix context, and downstream signaling branches collectively determine the final output. As a result, this pathway displays marked tissue specificity and context dependence.

Keywords: FGF; FGFR; fibroblast growth factor receptor; Klotho; RAS-MAPK; PI3K-AKT; PLCγ; developmental signaling pathway

1. Basic Composition of the FGF Family

1.1 Ligand Family

The FGF family contains a relatively large number of members and, in humans, generally includes FGF1 through FGF23, although not all members function in exactly the same manner. Based on mode of action and molecular characteristics, they can be broadly divided into paracrine, endocrine, and intracellular classes.

(1) Paracrine FGFs

These members include FGF1, FGF2, FGF4, FGF7, FGF8, FGF9, FGF10, and FGF18. They usually depend on heparan sulfate proteoglycans (HSPGs) to stabilize the ligand-receptor complex, act over short distances, and are more strongly associated with regulation of proliferation, differentiation, and migration within the local microenvironment.

(2) Endocrine FGFs

Representative members are FGF19, FGF21, and FGF23. These FGFs bind HSPGs relatively weakly and are therefore better suited for longer-range action in the fluid phase, but they usually require Klotho-family co-receptors to enable efficient signal recognition.

(3) Intracellular FGFs

Members such as the FGF11 subfamily are more strongly involved in intracellular regulatory processes and are generally not interpreted as classical secreted FGFR ligands. Accordingly, they are usually not treated as a main axis in studies of the classical FGF-FGFR pathway.

1.2 Receptor Family

The classical receptors of the FGF pathway are FGFR1, FGFR2, FGFR3, and FGFR4. All belong to the receptor tyrosine kinase family and share a similar modular structure, including extracellular immunoglobulin-like domains, a transmembrane region, and an intracellular tyrosine kinase domain. FGFR1-3 also possess important alternative splicing isoforms, particularly the IIIb and IIIc variants, and this difference directly determines the response spectrum of different tissues to FGF ligands.

Table 1. Basic Composition of the FGF Family and FGFR System

Category	Representative Members	Major Features
Paracrine FGFs	FGF1, FGF2, FGF7, FGF8, FGF10, FGF18, etc.	HSPG-dependent, primarily local in action
Endocrine FGFs	FGF19, FGF21, FGF23	Klotho-dependent, with more prominent systemic regulation
Classical receptors	FGFR1, FGFR2, FGFR3, FGFR4	Receptor tyrosine kinases mediating major signaling output
Accessory factors	HSPG, α-Klotho, β-Klotho	Determine ligand recognition efficiency and tissue specificity

2. Receptor Structure and Accessory Recognition Systems

2.1 Structural Features of FGFRs

The extracellular region of FGFRs generally contains three immunoglobulin-like domains, among which the D2 and D3 regions form the key interface for ligand recognition, while the acidic box region participates in receptor autoinhibition and conformational regulation. The intracellular kinase domain is responsible for phosphorylation of tyrosine residues and provides binding sites for downstream adaptor proteins.

2.2 Significance of Splice Variants

The IIIb/IIIc splicing differences of FGFR1, FGFR2, and FGFR3 are a major foundation of FGF pathway research. Different splice variants show distinct expression patterns in epithelial and mesenchymal tissues. As a result, the same FGF may exhibit completely different receptor preferences and biological outcomes in different tissue settings. In other words, tissue specificity in the FGF pathway is not determined simply by whether FGFR is present, but rather by which FGFR isoform is expressed.

2.3 Roles of HSPG and Klotho

HSPG is a key stabilizing factor in paracrine FGF signaling. It not only increases the efficiency of FGF-FGFR binding, but also participates in receptor dimerization and local gradient formation.

The Klotho family mainly serves endocrine FGFs. Among these, α-Klotho is more commonly associated with FGF23, whereas β-Klotho is more frequently involved in FGF19 and FGF21 signaling. Klotho is not merely an accessory molecule, but a key determinant of whether endocrine FGFs can be recognized by specific tissues.

3. Activation Mechanism of the FGF Pathway

3.1 Ligand Binding and Receptor Dimerization

Classical FGF pathway activation begins with binding of an FGF ligand to the extracellular domain of FGFR. In paracrine FGFs, this process usually also requires HSPG to form a stable FGF-FGFR-HSPG complex. Once this complex is formed, two FGFR molecules are brought into proximity and dimerize, thereby enabling trans-phosphorylation of the intracellular kinase domains.

3.2 Phosphorylation of Tyrosine Residues

After FGFR activation, multiple intracellular tyrosine residues become phosphorylated and form docking platforms for distinct downstream signaling molecules. Among these, FRS2 (fibroblast growth factor receptor substrate 2) is one of the most representative proximal adaptor proteins in the FGF pathway. Once phosphorylated, FRS2 can further recruit molecules such as GRB2, SOS, and GAB1, thereby connecting to the major RAS-MAPK and PI3K-AKT axes.

4. Major Downstream Signaling Branches

4.1 RAS-RAF-MEK-ERK Pathway

This is the most classical pro-proliferative and pro-differentiation output axis of the FGF pathway. After FGFR activation, the FRS2-GRB2-SOS complex promotes RAS activation, followed sequentially by activation of RAF, MEK, and ERK. This pathway mainly participates in cell-cycle progression, initiation of developmental programs, and remodeling of transcriptional profiles.

4.2 PI3K-AKT-mTOR Pathway

This pathway is mainly associated with cell survival, metabolism, and anti-apoptotic signaling. Through nodes such as FRS2 and GAB1, FGFR connects to PI3K, which then activates AKT and mTOR, thereby enhancing cellular tolerance to nutrient fluctuations, stress, and injury.

4.3 PLCγ Pathway

FGFR can also directly or indirectly activate PLCγ, leading to cleavage of PIP2 into IP3 and DAG and subsequently mobilizing intracellular Ca²⁺- and PKC-related responses. This branch is more commonly associated with migration, secretion, and local membrane-signaling events.

4.4 Other Branches

In specific cellular contexts, the FGF pathway can also influence branches such as STAT, SRC, JNK, and p38, although these do not dominate under all FGF stimulation conditions. In most cases, RAS-MAPK and PI3K-AKT remain the major framework for interpreting FGF signaling output.

Table 2. Major Downstream Branches of the FGF Pathway and Their Functional Biases

Downstream Pathway	Core Nodes	Major Functional Bias
RAS-RAF-MEK-ERK	FRS2, GRB2, RAS, ERK	Proliferation, development, differentiation, transcriptional remodeling
PI3K-AKT-mTOR	PI3K, AKT, mTOR	Survival, metabolism, anti-apoptosis
PLCγ-PKC-Ca²⁺	PLCγ, PKC, Ca²⁺	Migration, secretion, membrane signal regulation
Other branches	STAT, SRC, etc.	Context-dependent regulation

5. Major Biological Functions of the FGF Pathway

5.1 Embryonic Development and Organogenesis

The FGF pathway is one of the most important morphogenetic signaling systems in developmental biology. It participates in limb bud formation, patterning of the nervous system, skeletal development, and formation of organs such as the lung and kidney, and determines cell-fate choices through concentration gradients, ligand distribution, and receptor expression patterns. Many developmental processes involving positional specification and differentiation windows are closely linked to the spatiotemporal control of FGF signaling.

5.2 Tissue Homeostasis and Injury Repair

In adult tissues, the FGF pathway participates in epithelial renewal, angiogenesis, wound healing, and maintenance of stem-cell niches. For example, FGF2 has prominent roles in vascular and stromal responses, whereas FGF7 and FGF10 are more commonly associated with epithelial regeneration and tissue repair.

5.3 Bone and Cartilage Metabolism

FGFR3 is especially representative in the regulation of skeletal development. Excessively strong FGFR3 activation suppresses chondrocyte proliferation and skeletal elongation, and its dysregulation is therefore closely associated with skeletal developmental disorders. FGF18, FGFR3, and related axes are major research subjects in bone and cartilage biology.

5.4 Metabolic Regulation

FGF19, FGF21, and FGF23 occupy central positions in bile acid metabolism, energy metabolism, and phosphate-calcium homeostasis, respectively. In particular, FGF21 has become an important molecule in metabolic disease research because of its close association with lipid metabolism, glucose metabolism, and stress adaptation.

6. FGF Pathway Dysregulation and Disease Associations

6.1 Developmental Abnormalities and Genetic Diseases

Abnormalities in the FGF-FGFR system can lead to multiple developmental disorders. For example, activating mutations in FGFR2 and FGFR3 can cause craniofacial developmental abnormalities and skeletal dysplasia. These diseases demonstrate that the FGF pathway is not merely a pro-growth pathway, but rather a finely tuned regulatory system that is highly sensitive to signal intensity, timing, and tissue location.

6.2 Tumor-Associated Abnormalities

In many tumors, the FGF pathway can be aberrantly activated through the following mechanisms:

(1) FGFR gene amplification or overexpression

(2) Activating mutations or fusions in FGFR

(3) Autocrine or paracrine amplification of FGF ligands

(4) Cooperative activation of downstream PI3K-AKT or RAS-MAPK nodes

In tumors, the FGF pathway may function either as a driver signal or as an alternative pathway after drug resistance develops. Its research value therefore lies not only in whether it is abnormal, but also in whether it supports pathway compensation and survival maintenance.

6.3 Metabolic and Renal-Bone Disorders

The FGF23-α-Klotho axis is closely associated with phosphate metabolism, vitamin D balance, and mineral abnormalities related to chronic kidney disease. FGF19 and FGF21 are more commonly studied in the context of hepatic metabolism, lipid metabolism, and insulin sensitivity. This area indicates that the FGF pathway is not limited to cell proliferation biology, but is also deeply involved in maintenance of endocrine homeostasis.

7. Key Research Focuses and Common Readouts of the FGF Pathway

7.1 Receptor-Level Readouts

Studies of the FGF pathway usually begin with the FGFR expression profile, splice-isoform type, and phosphorylation status. Common indicators include total FGFR1-4 protein, receptor phosphorylation levels, and changes in membrane localization.

7.2 Proximal Signaling Readouts

FRS2 and its phosphorylation status are key readouts of proximal activation in the FGF pathway. Compared with other receptor tyrosine kinases, FRS2 has stronger indicator value in the FGF pathway, and is therefore highly useful for validating whether signaling is directly driven by FGFR.

7.3 Downstream Readouts

Common indicators include p-ERK, p-AKT, p-PLCγ, and, in some contexts, STAT-related markers. These readouts are used to define signaling bias and form the core basis for interpreting the biological outcomes of FGF signaling.

7.4 Functional Readouts

Common experiments include:

(1) Proliferation and colony-formation assays

(2) Migration and invasion assays

(3) Detection of differentiation markers

(4) Analysis of metabolism-related endpoints

Table 3. Common Experimental Readouts of the FGF Pathway

Research Level	Common Indicators	Major Significance
Receptor level	FGFR1-4 expression, receptor phosphorylation	Determines the starting point of pathway activation
Proximal signaling level	FRS2, p-FRS2	Determines whether direct FGFR signaling has occurred
Downstream level	p-ERK, p-AKT, p-PLCγ	Determines signaling bias
Functional level	Proliferation, migration, differentiation, metabolic endpoints	Determines biological consequences

8. Products Related to the FGF Pathway

Table 4. Product Table of Classical Paracrine FGF Ligands

Category	Catalog No.	Product Name	Grade and Purity	Suitable Research Direction / Use
Classical ligand	rp170413	Recombinant Human FGF acidic/FGF1 Protein	ActiBioPure™, Bioactive, Carrier Free, High performance, ≥95%(SDS-PAGE)	Used for classical FGF1-FGFR stimulation, receptor activation validation, and ligand supplementation experiments
Classical ligand	rp186550	Recombinant Human FGF basic/FGF2 Protein	Carrier Free,Bioactive,ActiBioPure™,High performance,PBS Only,≥90%(SDS-PAGE),See COA	Used for classical bFGF stimulation, establishment of proliferative responses, and FGFR-dependence validation
Classical ligand	rp145939	Recombinant Human FGF basic/FGF2/bFGF(155aa) Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,High performance,PBS Only,≥95%(SDS-PAGE)	Used for comparing different FGF2 conformations or formulation conditions
Classical ligand	rp148028	Recombinant Human KGF/FGF-7 Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,Azide Free,High performance,PBS Only,≥95%(SDS-PAGE)	Used for research on the FGF7-FGFR2b axis and epithelial repair
Classical ligand	rp145913	Recombinant human FGF10 protein (Active)	Animal Free,Carrier Free,Bioactive,ActiBioPure™,Azide Free,High performance,PBS Only,≥95%(SDS-PAGE)	Used for studies of the FGF10-FGFR2b axis, epithelial-mesenchymal interaction, and developmental models
Classical ligand	rp183678	Recombinant Human FGF-18 Protein	Carrier Free,Bioactive,ActiBioPure™,High performance,PBS Only,≥95%(SDS-PAGE),See COA	Used for research on FGF18-related bone and cartilage biology and the FGFR3 axis
Classical ligand	rp145972	Recombinant Human FGF8 Protein	ActiBioPure™, Bioactive, Animal Free, Carrier Free, Azide Free, High performance, ≥95%(SDS-PAGE)	Used for FGF8-related developmental signaling and ligand-specific stimulation studies
Classical ligand	rp181240	Recombinant Human FGF-9 Protein	Carrier Free,Bioactive,ActiBioPure™,High performance,His Tag,≥95%(SDS-PAGE),See COA	Used for FGF9-related developmental and stromal signaling studies
Classical ligand	rp179841	Recombinant Human FGF-4 Protein	Carrier Free,Bioactive,ActiBioPure™,High performance,PBS Only,≥95%(SDS-PAGE)	Used for FGF4-related embryonic development and receptor-response studies
Ligand detection antibody	Ab223235	FGF2 Mouse mAb	Carrier Free,ExactAb™,Azide Free,Validated,High performance,PBS Only,≥95%(SDS-PAGE),1.0 mg/mL	Used for FGF2 protein detection and validation of secretion levels
Ligand detection antibody	Ab007066	Recombinant FGF2 Antibody	ExactAb™, Validated, Recombinant, High performance, 0.103 mg/mL	Used for FGF2 protein detection and methodological validation

Table 5. Product Table of Endocrine FGFs and FGFR Receptors

Category	Catalog No.	Product Name	Grade and Purity	Suitable Research Direction / Use
Endocrine ligand	rp145934	Recombinant Human FGF19 Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,Azide Free,His Tag,≥98%(SDS-PAGE)	Used for studies of the FGF19-FGFR4 axis and hepatobiliary metabolism
Endocrine ligand	rp169669	Recombinant Human FGF-21 Protein	Carrier Free,Azide Free,His Tag,PBS Only,≥95%(SDS-PAGE)	Used for metabolic FGF21 branches and endocrine FGF signaling studies
Endocrine ligand	rp145903	Recombinant Human FGF-23 Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,High performance,His Tag,≥95%(SDS-PAGE),See COA	Used for research on the FGF23-Klotho axis and phosphate-calcium homeostasis
Ligand blocking antibody	Ab209904	1A6 (anti-FGF19)	Carrier Free, Recombinant, ExactAb™, Low Endotoxin, Azide Free, Validated, Animal Free, ≥95%(SDS-PAGE&SEC-HPLC), See COA	Used for FGF19 neutralization and determination of FGF19 dependence
Ligand blocking antibody	Ab170464	Burosumab (Anti-FGF23)	Carrier Free, Recombinant, ExactAb™, Azide Free, Validated, Animal Free, ≥95%(SDS-PAGE&SEC-HPLC), See COA	Used for FGF23 neutralization and intervention in endocrine FGF branches
Receptor protein	rp145988	Recombinant Human FGFR1 Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,Azide Free,High performance,His Tag,Fc Tag,≥95%(SDS-PAGE)	Used for FGFR1 binding, competition, and receptor reconstitution experiments
Receptor protein	rp146001	Recombinant Human FGFR2 Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,Azide Free,His Tag,Fc Tag,≥95%(SDS-PAGE)	Used for FGFR2 receptor binding and ligand-preference studies
Receptor protein	rp183618	Recombinant Human FGFR2 alpha (IIIb) Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,High performance,Fc Tag,PBS Only,≥90%(SDS-PAGE),See COA	Used for isoform-specific recognition studies of FGFR2 IIIb
Receptor protein	rp183619	Recombinant Human FGFR2 alpha (IIIc) Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,His Tag,≥95%(SDS-PAGE)	Used for isoform-specific recognition studies of FGFR2 IIIc
Receptor protein	rp184034	Recombinant Human FGFR3 (IIIc) Fc Chimera Protein	Animal Free,Carrier Free,Fc Tag,PBS Only,≥95%(SDS-PAGE),See COA	Used for studies of FGFR3 IIIc subtype binding and ligand selectivity
Receptor protein	rp183620	Recombinant Human FGFR4 Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,High performance,His Tag,PBS Only,≥95%(SDS-PAGE)	Used for FGFR4 binding and research on FGF19/FGF21 branches
Receptor detection antibody	Ab103359	Recombinant FGFR2 Antibody	ExactAb™, Validated, Recombinant, 1.5 mg/mL	Used for FGFR2 protein detection
Receptor detection antibody	Ab103377	Recombinant FGFR3 Antibody	Recombinant, ExactAb™, Validated, High performance, See COA	Used for FGFR3 protein detection
Receptor detection antibody	Ab103390	Recombinant FGFR4 Antibody	ExactAb™, Recombinant, Validated, See COA	Used for FGFR4 protein detection

Table 6. Product Table of FGF/FGFR Blocking Antibodies and Inhibitors

Category	Catalog No.	Product Name	Grade and Purity	Suitable Research Direction / Use
FGFR2 blocking antibody	Ab170493	Aprutumab (anti-FGFR2)	Carrier Free, Recombinant, ExactAb™, Low Endotoxin, Azide Free, Validated, Animal Free, ≥95%(SDS-PAGE&SEC-HPLC), See COA	Used for FGFR2 blockade and validation of FGFR2 dependence
FGFR2 blocking antibody	Ab170514	Bemarituzumab (anti-FGFR2)	Animal Free, Carrier Free, Recombinant, ExactAb™, Low Endotoxin, Azide Free, Validated, ≥95%(SDS-PAGE&SEC-HPLC), Lot by Lot	Used for FGFR2-targeted blockade and studies corresponding to therapeutic antibodies
FGFR3 blocking antibody	Ab176565	LY3076226 (anti-FGFR3)	Carrier Free, Recombinant, ExactAb™, Low Endotoxin, Azide Free, Validated, Animal Free, ≥95%(SDS-PAGE&SEC-HPLC), See COA	Used for FGFR3 blockade and FGFR3-dependent studies
FGFR3 blocking antibody	Ab177923	Vofatamab (anti-FGFR3)	Carrier Free, Recombinant, ExactAb™, Low Endotoxin, Azide Free, Validated, Animal Free, ≥95%(SDS-PAGE&SEC-HPLC), See COA	Used for FGFR3 pathway blockade and antibody comparison studies
FGFR4 blocking antibody	Ab177857	U3-1784 (anti-FGFR4)	Carrier Free, Recombinant, ExactAb™, Low Endotoxin, Azide Free, Validated, Animal Free, ≥95%(SDS-PAGE&SEC-HPLC), See COA	Used for FGFR4 blockade and studies of the FGF19-FGFR4 axis
Pan-FGFR inhibitor	A127209	AZD4547	Moligand™, ≥99%	Used for classical FGFR inhibition and pathway-dependence validation
Pan-FGFR inhibitor	N127052	BGJ398 (NVP-BGJ398)	Moligand™, ≥98%	Used for FGFR pathway inhibition and small-molecule control studies
Pan-FGFR inhibitor	C302315	CH5183284 (Debio-1347)	Moligand™, ≥99%	Used for FGFR kinase inhibition and comparison of sensitivity
Pan-FGFR inhibitor	T302895	Futibatinib	Moligand™, ≥98%	Used for studies of irreversible FGFR inhibition
Pan-FGFR inhibitor	L126507	LY2874455	Moligand™, ≥99%	Used for intervention across the overall FGF-FGFR axis
Pan-FGFR inhibitor	P135784	PD-161570	≥98%(HPLC)	Used for FGFR inhibition and historical benchmark-compound control
Pan-FGFR inhibitor	P132694	PD-166866	≥98%(HPLC)	Used for studies of FGFR tyrosine kinase inhibition
FGFR1/3 inhibitor	P125865	PD173074	Moligand™, ≥99%	Used for biased intervention studies targeting FGFR1/FGFR3
FGFR4-selective inhibitor	B174512	BLU-9931	Moligand™, ≥97%	Used for selective FGFR4 inhibition studies
FGFR4-selective inhibitor	R414051	Roblitinib (FGF401)	Moligand™, ≥98%	Used for classical validation of selective FGFR4 inhibition
Allosteric inhibitor	S275943	SSR128129E	≥98%	Used for studies of allosteric FGFR inhibition and mechanistic comparison
Pan-FGFR inhibitor	F648239	FGFR-IN-1	≥99%	Used for rapid validation of FGFR pathway inhibition
FGFR2-selective intervention	F1451299	FGFR2-IN-1	≥99%	Used for selective FGFR2 inhibition studies
FGFR3-selective intervention	F649421	FGFR3-IN-5		Used for selective FGFR3 inhibition studies
FGFR4-selective intervention	F649982	FGFR4-IN-1	≥99%	Used for selective FGFR4 inhibition studies
Targeted degrader	P1417873	PROTAC FGFR2 degrader 1		Used for FGFR2 protein degradation studies and non-simple inhibition models
Oligonucleotide intervention	I1451035	IONIS-FGFR4Rx		Used for post-transcriptional intervention targeting FGFR4

Table 7. Product Table of Quantitative Detection Reagents for the FGF/FGFR Pathway

Category	Catalog No.	Product Name	Grade and Purity	Suitable Research Direction / Use
Human ligand ELISA	EJ1514426	Human Fibroblast Growth Factor 2, Basic (FGF2/bFGF) ELISA Kit	BioReagent	Used for quantitative detection of FGF2/bFGF secretion
Human ligand ELISA	EJ1514122	Human Fibroblast Growth Factor 10 (FGF-10) ELISA Kit	BioReagent	Used for quantitative detection of FGF10
Human ligand ELISA	EJ1514124	Human Fibroblast Growth Factor 18 (FGF-18) ELISA Kit	BioReagent	Used for quantitative detection of FGF18
Human ligand ELISA	EJ1514125	Human Fibroblast Growth Factor 19 (FGF-19) ELISA Kit	BioReagent	Used for quantitative detection of FGF19
Human ligand ELISA	EJ1514127	Human Fibroblast Growth Factor 21 (FGF-21) ELISA Kit	BioReagent	Used for quantitative detection of FGF21
Human ligand ELISA	EJ1514128	Human Fibroblast Growth Factor 23 (FGF-23) ELISA Kit	BioReagent	Used for quantitative detection of FGF23
Human receptor ELISA	EJ1514136	Human Fibroblast Growth Factor Receptor 1 (FGFR1) ELISA Kit	BioReagent	Used for quantitative detection of FGFR1
Human receptor ELISA	EJ1514137	Human Fibroblast Growth Factor Receptor 2 (FGFR2) ELISA Kit	BioReagent	Used for quantitative detection of FGFR2
Human receptor ELISA	EJ1514138	Human Fibroblast Growth Factor Receptor 3 (FGFR3) ELISA Kit	BioReagent	Used for quantitative detection of FGFR3
Human receptor ELISA	EJ1514139	Human Fibroblast Growth Factor Receptor 4 (FGFR4) ELISA Kit	BioReagent	Used for quantitative detection of FGFR4
Mouse ligand ELISA	EJ1512795	Mouse Fibroblast Growth Factor 21 (FGF21) ELISA Kit	BioReagent	Used for quantitative detection of mouse FGF21
Mouse ligand ELISA	EJ1512802	Mouse Fibroblast Growth Factor 23 (FGF-23) ELISA Kit	BioReagent	Used for quantitative detection of mouse FGF23
Rat ligand ELISA	EJ1512076	Rat Fibroblast Growth Factor 21 (FGF-21) ELISA Kit	BioReagent	Used for quantitative detection of rat FGF21
Rat ligand ELISA	EJ1512077	Rat Fibroblast Growth Factor 23 (FGF-23) ELISA Kit	BioReagent	Used for quantitative detection of rat FGF23

The core of the FGF pathway lies not merely in FGF-FGFR binding, but in a stratified signaling network jointly defined by ligand subgroups, receptor isoforms, HSPG- or Klotho-mediated recognition systems, and multiple downstream signaling axes.

For more related articles, please see below:

[1] Ras-Raf-MEK-ERK Signaling

[2] Wnt/β-Catenin Signaling Pathway

[3] How to Map the NF-κB Pathway and Choose Inhibitors: Bringing Inflammatory Transcriptional Output into a “Controllable Range” (Tables A–F)

[4] Metabolic signaling pathway

[5] Wnt Signaling

[6] Hedgehog Signaling

[7] JAK-STAT Cell Signaling Pathway

[8] PD-1/PD-L1 Signaling Pathway

References

[1] Cotton LM, O'Bryan MK, Hinton BT. Cellular signaling by fibroblast growth factors (FGFs) and their receptors (FGFRs) in male reproduction. Endocr Rev. 2008 Apr;29(2):193-216.

[2] Kurdziel KA, Lindenberg L, Choyke PL. Oncologic angiogenesis imaging in the clinic—how and why. Imaging Med. 2011 Sep;3(4):445-457.

[3] Ballas MS, Chachoua A. Rationale for targeting VEGF, FGF, and PDGF for the treatment of NSCLC. Onco Targets Ther. 2011;4:43-58.

[4] Rose BA, Force T, Wang Y. Mitogen-activated protein kinase signaling in the heart: angels versus demons in a heart-breaking tale. Physiol Rev. 2010 Oct;90(4):1507-1546.

[5] Turner N, Grose R. Fibroblast growth factor signalling: from development to cancer. Nat Rev Cancer. 2010 Feb;10(2):116-129.