Fibroblast growth factor 20 gene and Parkinson's disease in the Japanese population

FGF20

Fibroblast growth factor 20 (FGF20) is a neurotrophic factor and a member of the FGF9 subfamily. It was first identified in Xenopus embryos and was isolated shortly thereafter from the adult rat brain. Its receptors include FGFR4, FGFR3b, FGFR2b and the FGFRc splice forms. In adults it is highly expressed in the brain, while it is expressed in a variety of regions during embryonic development, including the inner ear, heart, hair placodes, mammary buds, dental epithelium and limbs. As a result of its wide-spread expression, FGF20 mouse mutants exhibit a variety of phenotypes including congenital deafness, lack of hair, small kidneys and delayed mammary ductal outgrowth. FGF20 is also associated with human diseases including Parkinson's Disease, cancer and hereditary deafness.

Quantitative assessment of the effect of FGF20 rs1721100 and rs12720208 variant on the risk of sporadic Parkinson's disease: a meta-analysis

OBJECTIVES

While many studies have investigated the associations between fibroblast growth factor 20 (FGF20) rs1721100 (C/G) and rs12720208 (C/T) polymorphisms and susceptibility to Parkinson's disease (PD), their results are controversial. Our present meta-analysis estimated the overall association between FGF20 rs1721100 and rs12720208 polymorphisms and the risk of sporadic PD.

METHODS

We performed a comprehensive literature search of the PubMed, Web of Science, Embase, Chinese National Knowledge Infrastructure, and Wanfang Medicine electronic databases, which was updated in April 2021. Based on strict inclusion and exclusion criteria, the analysis included a total of 10 papers involving 14 studies with 5262 cases of PD and 6075 controls. Review Manager 5.4 software was used to assess the available data from each study. The pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the association between the FGF20 rs1721100 and rs12720208 polymorphisms and sporadic PD risk.

RESULTS

Our results showed that the FGF20 rs1721100 G allele frequency and genotype distribution did not differ between PD patients and controls. Similarly, the FGF20 rs12720208 T allele frequency and genotype distribution did not differ significantly between the two groups. A subgroup analysis of Asian and Caucasian populations also showed the same results.

CONCLUSIONS

The results of this meta-analysis indicated that neither the rs1721100 C/G nor the rs12720208 C/T variants were associated with sporadic PD susceptibility.

Fibroblast Growth Factor 20 Gene Polymorphism in Parkinson's Disease in Asian Population: A Meta-Analysis

Parkinson's disease (PD) is a neurodegenerative disease with the pathological hallmark of Lewy bodies and Lewy neurites composed of α-synuclein. The SNP rs591323 is one of the risk loci located near the FGF20 gene that has been implicated in PD. The variation of FGF20 in the 3' untranslated region was shown to increase α-synuclein expression. We examined the association of rs591323 with the risk of PD in a Taiwanese population and conducted a meta-analysis, including our study and two other studies from China, to further confirm the role of this SNP in Taiwanese/Chinese populations. A total of 586 patients with PD and 586 health controls (HCs) were included in our study. We found that the minor allele (A) and the AA + GA genotype under the dominant model are significantly less frequent in PD than in controls. The meta-analysis consisted of 1950 patients with PD and 2073 healthy controls from three studies. There was significant association between rs591323 and the risk of PD in the additive (Z = -3.96; p < 0.0001) and the dominant models (Z = -4.01; p < 0.0001). Our study results and the meta-analysis support the possible protective role of the rs591323 A allele in PD in Taiwanese/Chinese populations.

Parkinson's disease and pesticides: Are microRNAs the missing link?

Parkinson's disease (PD) is a common neurodegenerative disorder that leads to significant morbidity and decline in the quality of life. It develops due to loss of dopaminergic neurons in the substantia nigra pars compacta, and among its pathogenic factors oxidative stress plays a critical role in disease progression. Pesticides are a broad class of chemicals widely used in agriculture and households for the protection of crops from insects and fungi. Several of them have been incriminated as risk factors for PD, but the underlying mechanisms have yet to be fully understood. MicroRNAs (miRNAs) are small, non-coding RNA molecules that play an important role in regulating mRNA translation and protein synthesis. miRNA levels have been shown to be affected in several diseases as well. Since the studies on the association between pesticides and PD have yet to reach definitive conclusions, here we review recent evidence on deregulated microRNAs upon pesticide exposure, and attempt to find an overlap between miRNAs deregulated in PD and pesticides, as a missing link between the two, and enhance future research in this direction.

The potential role of neuroinflammation and transcription factors in Parkinson disease

Parkinson disease (PD) is a neurodegenerative disorder characterized by dopaminergic neurons affected by inflammatory processes. Post-mortem analyses of brain and cerebrospinal fluid from PD patients show the accumulation of proinflammatory cytokines, confirming an ongoing neuroinflammation in the affected brain regions. These inflammatory mediators may activate transcription factors—notably nuclear factor κB, Ying-Yang 1 (YY1), fibroblast growth factor 20 (FGF20), and mammalian target of rapamycin (mTOR)—which then regulate downstream signaling pathways that in turn promote death of dopaminergic neurons through death domain-containing receptors. Dopaminergic neurons are vulnerable to oxidative stress and inflammatory attack. An increased level of inducible nitric oxide synthase observed in the substantia nigra and striatum of PD patients suggests that both cytokine—and chemokine-induced toxicity and inflammation lead to oxidative stress that contributes to degeneration of dopaminergic neurons and to disease progression. Lipopolysaccharide activation of microglia in the proximity of dopaminergic neurons in the substantia nigra causes their degeneration, and this appears to be a selective vulnerability of dopaminergic neurons to inflammation. In this review, we will look at the role of various transcription factors and signaling pathways in the development of PD.

An evidence-based approach to identify aging-related genes in Caenorhabditis elegans

Background

Extensive studies have been carried out on Caenorhabditis elegans as a model organism to elucidate mechanisms of aging and the effects of perturbing known aging-related genes on lifespan and behavior. This research has generated large amounts of experimental data that is increasingly difficult to integrate and analyze with existing databases and domain knowledge. To address this challenge, we demonstrate a scalable and effective approach for automatic evidence gathering and evaluation that leverages existing experimental data and literature-curated facts to identify genes involved in aging and lifespan regulation in C. elegans.

Results

We developed a semantic knowledge base for aging by integrating data about C. elegans genes from WormBase with data about 2005 human and model organism genes from GenAge and 149 genes from GenDR, and with the Bio2RDF network of linked data for the life sciences. Using HyQue (a Semantic Web tool for hypothesis-based querying and evaluation) to interrogate this knowledge base, we examined 48,231 C. elegans genes for their role in modulating lifespan and aging. HyQue identified 24 novel but well-supported candidate aging-related genes for further experimental validation.

Conclusions

We use semantic technologies to discover candidate aging genes whose effects on lifespan are not yet well understood. Our customized HyQue system, the aging research knowledge base it operates over, and HyQue evaluations of all C. elegans genes are freely available at http://hyque.semanticscience.org.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0469-4) contains supplementary material, which is available to authorized users.

Quantitative assessment of the association between fibroblast growth factor 20 rs1721100 C/G polymorphism and the risk of sporadic Parkinson's diseases: a meta-analysis

Fibroblast growth factor 20 (FGF20) is a neurotrophic factor which enhances the survival of rat midbrain dopamine neurons. Genetic variation in FGF20 may influence the risk of occurrence and development in Parkinson's diseases (PD). Many studies have evaluated the association between FGF20 rs1721100 C/G polymorphism and the risk of sporadic PD; however, published data are still controversial. The aim of the present meta-analysis was to evaluate the association of FGF20 rs1721100 C/G polymorphism with susceptibility of PD. The summary odds ratio (OR) with its 95 % confidence interval (CI) was calculated to estimate the association. Five case-control studies with a total of 3,463 sporadic PD cases and 4,606 controls were finally included into this meta-analysis. Neither the basic allele frequencies nor the genotypic distributions of rs1721100 C/G within FGF20 were different between two groups when all studies were pooled into the meta-analysis. Subgroup analysis by ethnicity showed FGF20 rs1721100 C/G polymorphism was significantly associated with increased risk in the heterozygote comparison model (CG versus GG: OR = 0.83, 95 % CI, 0.72-0.95, P = 0.009) in Asians but not in Caucasians. Overall, this meta-analysis suggests that FGF20 rs1721100 C/G polymorphism is associated with sporadic PD in Asians.

Deficiency of zebrafish fgf20a results in aberrant skull remodeling that mimics both human cranial disease and evolutionarily important fish skull morphologies

The processes that direct skull remodeling are of interest to both human-oriented studies of cranial dysplasia and evolutionary studies of skull divergence. There is increasing awareness that these two fields can be mutually informative when natural variation mimics pathology. Here we describe a zebrafish mutant line, devoid of blastema (dob), which does not have a functional fgf20a protein, and which also presents cranial defects similar to both adaptive and clinical variation. We used geometric morphometric methods to provide quantitative descriptions of the effects of the dob mutation on skull morphogenesis. In combination with "whole-mount in situ hybridization" labeling of normal fgf20a expression and assays for osteoblast and osteoclast activity, the results of these analyses indicate that cranial dysmorphologies in dob zebrafish are generated by aberrations in post-embryonic skull remodeling via decreased osteoblasotgenesis and increased osteoclastogenesis. Mutational effects include altered skull vault geometries and midfacial hypoplasia that are consistent with key diagnostic signs for multiple human craniofacial syndromes. These phenotypic shifts also mimic changes in the functional morphology of fish skulls that have arisen repeatedly in several highly successful radiations (e.g., damselfishes and East-African rift-lake cichlids). Our results offer the dob/fgf20a mutant as an experimentally tractable model with which to examine post-embryonic skull development as it relates to human disease and vertebrate evolution.

Polymorphisms affecting miRNA regulation: a new level of genetic variation affecting disorders and diseases of the human CNS

The recognition of people and/or populations at a high risk for the development of various types of neurological disorders and diseases is not only key to improved screening programs and earlier detection, but it also provides hope for appropriate treatment and care. Genetic alterations that change gene-expression levels have long been investigated for association with the development of pathological neurological conditions. Gene regulation by miRNAs is a relatively new area of study, and published evidence suggests that alterations in this process may be associated with increased disease risk. Here, the authors review the current data for association between single nucleotide polymorphisms (SNPs) and miRNA-mediated gene regulation (miR-SNPs) in human neuropsychiatric and neurodegenerative diseases. Additionally, we present an approach to detect and identify functional miR-SNPs for the purpose of carrying out large-scale genetic association studies. The growing body of literature suggests that miR-SNPs are emerging as a powerful tool, both to study the pathobiology of diseases, as well as aiding in its diagnosis and prognosis.

Roles of FGF20 in dopaminergic neurons and Parkinson's disease

The fibroblast growth factor (FGF) family comprises 22 members with diverse functions in development and metabolism. Fgf20 was originally identified as a new Fgf preferentially expressed in the substantia nigra pars compacta (SNpc). Fgf20, which acts on proximal cells, significantly enhanced the survival of cultured dopaminergic neurons by activating the mitogen-activated protein kinase (MAPK) pathway through Fgf receptor 1c. In the rat model of Parkinson's disease, Fgf20 afforded significant protection against the loss of dopaminergic neurons. The significant correlation of Parkinson's disease with single-nucleotide polymorphisms in FGF20 indicates that the genetic variability of FGF20 can be a Parkinson's disease risk. Neural and embryonic stem (ES) cells have been considered as cell resources for restorative transplantation strategies in Parkinson's disease. Fgf20 promoted the differentiation of these stem cells into dopaminergic neurons, which attenuated neurological symptoms in animal models of Parkinson's disease. These findings indicate the importance of FGF20 for the differentiation and survival of dopaminergic neurons and the etiology and therapy of Parkinson's disease.

Fibroblast growth factor-20 protects against dopamine neuron loss in vitro and provides functional protection in the 6-hydroxydopamine-lesioned rat model of Parkinson's disease

Fibroblast growth factor-20 (FGF-20) has been shown to protect dopaminergic neurons against a range of toxic insults in vitro, through activation of fibroblast growth factor receptor 1 (FGFR1). This study set out to examine whether FGF-20 also displayed protective efficacy in the unilateral, 6-hydroxydopamine (6-OHDA) lesion rat model of Parkinson's disease. Initial studies demonstrated that, in embryonic ventral mesencephalic (VM) cultures, FGFR1 was expressed on tyrosine hydroxylase (TH)-positive neurons and that, in line with previous data, FGF-20 (100 and 500 ng/ml) almost completely protected these TH-positive neurons against 6-OHDA-induced toxicity. Co-localisation of FGFR1 and TH staining was also demonstrated in the substantia nigra pars compacta (SNpc) of naïve adult rat brain. In animals subject to 6-OHDA lesion of the nigrostriatal tract, supra-nigral infusion of FGF-20 (2.5 μg/day) for 6 days post-lesion gave significant protection (∼40%) against the loss of TH-positive cells in the SNpc and the loss of striatal TH immunoreactivity. This protection of the nigrostriatal tract was accompanied by a significant preservation of gross locomotion and fine motor movements and reversal of apomorphine-induced contraversive rotations, although forelimb akinesia, assessed using cylinder test reaching, was not improved. These results support a role for FGF-20 in preserving dopamine neuron integrity and some aspects of motor function in a rodent model of Parkinson's disease (PD) and imply a potential neuroprotective role for FGF-20 in this disease.

A genome-wide linkage screen in the Amish with Parkinson disease points to chromosome 6

Parkinson disease (PD) is a common complex neurodegenerative disorder with an underlying genetic etiology that has been difficult to dissect. Although some PD risk genes have been discovered, most of the underlying genetic etiology remains unknown. To further elucidate the genetic component, we have undertaken a genome-wide linkage screen in an isolated founder population of Amish living in the Midwestern United States. We performed tests for linkage and for association using a marker set of nearly 6000 single-nucleotide polymorphisms. Parametric multipoint linkage analysis generated a logarithm of the odds of linkage (LOD) score of 2.44 on chromosome 6 in the SYNE1 gene, approximately 8 Mbp from the PARK2 gene. In a different region on chromosome 6 (∼67 Mbp from PARK2) an association was found for rs4302647 (p < 4.0 × 10(-6) ), which is not within 300 kb of any gene. While the association exceeds Bonferroni correction, it may yet represent a false positive due to the small sample size and the low minor allele frequency. The minor allele frequency in affecteds is 0.07 compared to 0.01 in unaffecteds. Taken together, these results support involvement of loci on chromosome 6 in the genetic etiology of PD.

MicroRNAs in Parkinson's disease

MicroRNAs are small non-protein coding RNAs that regulate gene expression through post-transcriptional repression. Recent studies demonstrated the importance of microRNAs in the nervous system development, function and disease. Parkinson's disease is the second most prevalent neurodegenerative disease with only symptomatic treatment available. Recent success in using small RNAs as therapeutic targets hold a substantial promise for the Parkinson's disease field. Here we review recent work linking the microRNA pathway to Parkinson's disease.

Genetic variation in FGF20 modulates hippocampal biology

We explored the effect of single-nucleotide polymorphisms (SNPs) in the fibroblast growth factor 20 gene (FGF20) associated with risk for Parkinson's disease on brain structure and function in a large sample of healthy young-adult human subjects and also in elderly subjects to look at the interaction between genetic variations and age (N = 237; 116 men; 18-87 years). We analyzed high-resolution anatomical magnetic resonance images using voxel-based morphometry, a quantitative neuroanatomical technique. We also measured FGF20 mRNA expression in postmortem human brain tissue to determine the molecular correlates of these SNPs (N = 108; 72 men; 18-74 years). We found that the T allele carriers of rs12720208 in the 3'-untranslated region had relatively larger hippocampal volume (p = 0.0059) and diminished verbal episodic memory (p = 0.048) and showed steeper decreases of hippocampal volume with normal aging (p = 0.026). In postmortem brain, T allele carriers had greater expression of hippocampal FGF20 mRNA (p = 0.037), consistent with a previously characterized microRNA mechanism. The C allele matches a predicted miR-433 microRNA binding domain, whereas the T allele disrupts it, resulting in higher FGF20 protein translation. The strong FGF20 genetic effects in hippocampus are presumably mediated by activation of the FGFR1 (FGF receptor 1), which is expressed in mammalian brain most abundantly in the hippocampus. These associations, from mRNA expression to brain morphology to cognition and an interaction with aging, confirm a role of FGF20 in human brain structure and function during development and aging.

FGF20 rs12720208 SNP and microRNA-433 variation: no association with Parkinson's disease in Spanish patients

DNA variation at the FGF20 gene has been associated with Parkinson's disease (PD). In particular, SNP rs12720208 in the 3' untranslated region (3' UTR) was linked to PD-risk through a mechanism that would implicate a differential binding to microRNA-433 (miR-433). The reduction of the affinity of miR-433 to the 3' UTR would result in increased FGF20 expression and upregulation of alpha-synuclein, which could in turn promote dopaminergic neurons degeneration. We genotyped the rs12720208 SNP in a total of 512 PD patients and 258 healthy controls from Spain, and searched for miR-433 variants in the patients. We did not find significant differences in allele and genotype frequencies between patients and controls. None of the patients had miR-433 variants. In conclusion, our work did not confirm the association between rs12720208 and PD, or an effect of miR-433 variants on this disease.

FGF20 and Parkinson's disease: no evidence of association or pathogenicity via alpha-synuclein expression

Genetic variation in fibroblast growth factor 20 (FGF20) has been associated with risk of Parkinson's disease (PD). Functional evidence suggested the T allele of one SNP, rs12720208 C/T, altered PD risk by increasing FGF20 and alpha-synuclein protein levels. Herein we report our association study of FGF20 and PD risk in four patient-control series (total: 1,262 patients and 1,881 controls), and measurements of FGF20 and alpha-synuclein protein levels in brain samples (nine patients). We found no evidence of association between FGF20 variability and PD risk, and no relationship between the rs12720208 genotype, FGF20 and alpha-synuclein protein levels.

Chromosome 8p as a potential hub for developmental neuropsychiatric disorders: implications for schizophrenia, autism and cancer

Defects in genetic and developmental processes are thought to contribute susceptibility to autism and schizophrenia. Presumably, owing to etiological complexity identifying susceptibility genes and abnormalities in the development has been difficult. However, the importance of genes within chromosomal 8p region for neuropsychiatric disorders and cancer is well established. There are 484 annotated genes located on 8p; many are most likely oncogenes and tumor-suppressor genes. Molecular genetics and developmental studies have identified 21 genes in this region (ADRA1A, ARHGEF10, CHRNA2, CHRNA6, CHRNB3, DKK4, DPYSL2, EGR3, FGF17, FGF20, FGFR1, FZD3, LDL, NAT2, NEF3, NRG1, PCM1, PLAT, PPP3CC, SFRP1 and VMAT1/SLC18A1) that are most likely to contribute to neuropsychiatric disorders (schizophrenia, autism, bipolar disorder and depression), neurodegenerative disorders (Parkinson's and Alzheimer's disease) and cancer. Furthermore, at least seven nonprotein-coding RNAs (microRNAs) are located at 8p. Structural variants on 8p, such as copy number variants, microdeletions or microduplications, might also contribute to autism, schizophrenia and other human diseases including cancer. In this review, we consider the current state of evidence from cytogenetic, linkage, association, gene expression and endophenotyping studies for the role of these 8p genes in neuropsychiatric disease. We also describe how a mutation in an 8p gene (Fgf17) results in a mouse with deficits in specific components of social behavior and a reduction in its dorsomedial prefrontal cortex. We finish by discussing the biological connections of 8p with respect to neuropsychiatric disorders and cancer, despite the shortcomings of this evidence.

Genome-wide linkage screen in familial Parkinson disease identifies loci on chromosomes 3 and 18

Parkinson disease (PD) is a complex, multifactorial neurodegenerative disease with substantial evidence for genetic risk factors. We conducted a genome-wide linkage screen of 5824 single-nucleotide polymorphisms in 278 families of European, non-Hispanic descent to localize regions that harbor susceptibility loci for PD. By using parametric and nonparametric linkage analyses and allowing for genetic heterogeneity among families, we found two loci for PD. Significant evidence for linkage was detected on chromosome 18q11 (maximum lod score [MLOD] = 4.1) and suggestive evidence for linkage was obtained on chromosome 3q25 (MLOD = 2.5). These results were strongest in families not previously screened for linkage, and simulation studies suggest that these findings are likely due to locus heterogeneity rather than random statistical error. The finding of two loci (one highly statistically significant) suggests that additional PD susceptibility genes might be identified through targeted candidate gene studies in these regions.

Calbindin 1, fibroblast growth factor 20, and alpha-synuclein in sporadic Parkinson's disease

Parkinson's disease (PD), one of the most common human neurodegenerative disorders, is characterized by the loss of dopaminergic neurons in the substantia nigra of the midbrain. Our recent case-control association study of 268 SNPs in 121 candidate genes identified alpha-synuclein (SNCA) as a susceptibility gene for sporadic PD (P = 1.7 x 10(-11)). We also replicated the association of fibroblast growth factor 20 (FGF20) with PD (P = 0.0089). To find other susceptibility genes, we added 34 SNPs to the previous screen. Of 302 SNPs in a total 137 genes, but excluding SNCA, SNPs in NDUFV2, FGF2, CALB1 and B2M showed significant association (P < 0.01; 882 cases and 938 control subjects). We replicated the association analysis for these SNPs in a second independent sample set (521 cases and 1,003 control subjects). One SNP, rs1805874 in calbindin 1 (CALB1), showed significance in both analyses (P = 7.1 x 10(-5); recessive model). When the analysis was stratified relative to the SNCA genotype, the odds ratio of CALB1 tended to increase according to the number of protective alleles in SNCA. In contrast, FGF20 was significant only in the subgroup of SNCA homozygote of risk allele. CALB1 is a calcium-binding protein that widely is expressed in neurons. A relative sparing of CALB1-positive dopaminergic neurons is observed in PD brains, compared with CALB1-negative neurons. Our genetic analysis suggests that CALB1 is associated with PD independently of SNCA, and that FGF20 is associated with PD synergistically with SNCA.

Functional evolutionary history of the mouse Fgf gene family

Fibroblast Growth Factors (FGFs) are polypeptides with diverse activities in development and physiology. The mammalian Fgf family can be divided into the intracellular Fgf11/12/13/14 subfamily (iFGFs), the hormone-like Fgf15/21/23 subfamily (hFGFs), and the canonical Fgf subfamilies, including Fgf1/2/5, Fgf3/4/6, Fgf7/10/22, Fgf8/17/18, and Fgf9/16/20. However, all Fgfs are evolutionarily related. We propose that an Fgf13-like gene is the ancestor of the iFgf subfamily and the most likely evolutionary ancestor of the entire Fgf family. Potential ancestors of the canonical and hFgf subfamilies, Fgf4-, Fgf5-, Fgf8-, Fgf9-, Fgf10-, and Fgf15-like, appear to have derived from an Fgf13-like ancestral gene. Canonical FGFs function in a paracrine manner, while hFGFs function in an endocrine manner. We conclude that the ancestral Fgfs for these subfamilies acquired this functional diversity before the evolution of vertebrates. During the evolution of early vertebrates, the Fgf subfamilies further expanded to contain three or four members in each subfamily.

Gene-gene interaction between FGF20 and MAOB in Parkinson disease

The fibroblast growth factor 20 (FGF20) and monoamine oxidase B (MAOB) genes are associated with Parkinson Disease (PD) risk and both are in the dopamine bio-pathway. Therefore, we investigated the joint effect between polymorphisms in the FGF20 and MAOB genes for evidence of interaction contributing to PD risk. Fourteen polymorphisms (eight for FGF20, six for MAOB) were genotyped in 736 families and analyzed using conditional logistic regression (CLR). Significant two-locus interactions were found in females between the polymorphisms rs1721100 of FGF20 and rs1799836 of MAOB, and between the polymorphisms rs1721082 of FGF20 and rs1799836 of MAOB. The risk alleles for each SNP identified from CLR, rs1721100 C, rs1721082 T and rs1799836 A, are consistent with previous reports. Using indicator variables for the SNP genotypes, rs1721100 GC with rs1799836 AA showed significant interaction (P = 0.021), compared with the reference group rs1721100 GG with rs1799836 GG. Using an allele-dose model for the risk alleles, rs1721100 and rs1799836 showed significant interaction (P = 0.019). We found similar interaction results between rs1721082 and rs1799836. In conclusion, variants in FGF20 and MAOB show evidence of statistical interactions, which emphasizes the importance of considering them jointly in genetic analysis of PD and illustrates potential patterns of biological interaction contributing to PD risk.

The Fgf families in humans, mice, and zebrafish: their evolutional processes and roles in development, metabolism, and disease

Fibroblast growth factors (Fgfs) were originally isolated as growth factors for fibroblasts. However, Fgfs are now recognized as polypeptide growth factors of ca. 150-250 amino acid residues with diverse biological activities and expression profiles. The Fgf signaling system has been identified in multicelluar but not in unicellular organisms. In contrast to the only two Fgf genes and one Fgf receptor (Fgfr) gene in Caenorhabditis elegans, both the human and mouse Fgf and Fgfr gene families comprise twenty-two and four members, respectively. Their evolutional processes indicate that the Fgf and Fgfr gene families greatly co-expanded during the evolution of early vertebrates. The expansion of the Fgf and Fgfr gene families has enabled this signaling system to acquire diversity of function and a nearly ubiquitous involvement in many developmental and physiological processes. The zebrafish fgf gene family comprises twenty-seven members with several paralogs generated by an additional genome duplication. The mouse and zebrafish are useful models for studying gene functions. Fgf knockout mice have been generated. Several Fgf knockout mice die in the embryonic or early postnatal stages, indicating crucial roles for these genes in various developmental processes. However, other Fgf knockout mice survive with subtle phenotypic alterations. Their functions might be redundant. Studies using zebrafish embryos with mutated or knockdown fgfs also indicate that fgfs play crucial roles in development in that species. Although most Fgfs act in development in a paracrine and/or autocrine manner, some have potential roles in metabolism in an endocrine manner. In humans, Fgf signaling disorders result in hereditary diseases and cancers.