Xenopus laevis FGF16 activates the expression of genes coding for the transcription factors Sp5 and Sp5l

Fibroblast growth factors (FGFs) comprise a family of signalling molecules with essential roles in early embryonic development across animal species. The role of FGFs in mesoderm formation and patterning in Xenopus has been particularly well studied. However, little is known about FGF16 in Xenopus. Using in situ hybridisation, we uncover the expression pattern of FGF16 during early Xenopus laevis development, which has not been previously described. We show that the zygotic expression of FGF16 is activated in the mesoderm of the early gastrula as a ring around the blastopore, with its first accumulation at the dorsal side of the embryo. Later, FGF16 expression is found in the otic vesicle, the branchial arches and the anterior pituitary, as well as in the chordal neural hinge region of the tailbud. In addition, we show that FGF16 can activate the MAPK pathway and expression of sp5 and sp5l. Like FGF16, sp5 is expressed in the otic vesicle and the branchial arches, with all three of these genes being expressed in the tailbud. These data provide evidence that FGF16 is present in the early mesoderm and can activate the expression of developmentally important transcription factors.

Molecular insights into the klotho-dependent, endocrine mode of action of fibroblast growth factor 19 subfamily members

Unique among fibroblast growth factors (FGFs), FGF19, -21, and -23 act in an endocrine fashion to regulate energy, bile acid, glucose, lipid, phosphate, and vitamin D homeostasis. These FGFs require the presence of Klotho/betaKlotho in their target tissues. Here, we present the crystal structures of FGF19 alone and FGF23 in complex with sucrose octasulfate, a disaccharide chemically related to heparin. The conformation of the heparin-binding region between beta strands 10 and 12 in FGF19 and FGF23 diverges completely from the common conformation adopted by paracrine-acting FGFs. A cleft between this region and the beta1-beta2 loop, the other heparin-binding region, precludes direct interaction between heparin/heparan sulfate and backbone atoms of FGF19/23. This reduces the heparin-binding affinity of these ligands and confers endocrine function. Klotho/betaKlotho have evolved as a compensatory mechanism for the poor ability of heparin/heparan sulfate to promote binding of FGF19, -21, and -23 to their cognate receptors.

Comparative genomics on FGF16 orthologs

We have previously reported comparative genomics analyses on FGF3, FGF4, FGF6, FGF7, FGF8, FGF10, FGF11, FGF17, FGF18, FGF19, FGF20, FGF22 and FGF23 genes. Here, we performed comparative genomics analyses on FGF1, FGF2, FGF5, FGF9, FGF12, FGF13, FGF14, FGF16 and FGF21 genes, and further characterized the FGF16 gene. Chimpanzee FGF16, chicken fgf16, and zebrafish fgf16 genes were identified within NW_121938.1, NW_060344.1, and CR855117.3 genome sequences, respectively. Chimpanzee FGF16 (207 aa), chicken fgf16 (207 aa), and zebrafish fgf16 (203 aa) showed 100%, 89.9%, and 79.2% total amino-acid identity with human FGF16. Because FGF16, FGF9, and FGF20 constitute FGF subfamily without N-terminal signal peptide, we next searched for uncharacterized FGF9 or FGF20 orthologs. Zebrafish fgf9 gene was identified within BX927112.11 genome sequence, and chicken fgf20 gene within NW_060349.1 genome sequence. Although N-terminal part was divergent, middle and C-terminal parts were well conserved among vertebrate FGF16, FGF9 and FGF20 orthologs. Phylogenetic analyses revealed that zebrafish fgf9 and fgf20 were more related to each other than to their chicken or mammalian orthologs. TCF/LEF binding site and TATA box were well conserved among the human FGF16, rat Fgf16, and mouse Fgf16 promoters. Because nuclear complex consisting of TCF/LEF (TCF1, TCF3, TCF4 or LEF1), beta-catenin, PYGO (PYGO1 or PYGO2) and Legless (BCL9 or BCL9L) binds to the TCF/LEF-binding site to up-regulate WNT/beta-catenin target genes, FGF16 gene was characterized as the evolutionarily conserved target of the WNT/beta-catenin signaling pathway, just like FGF18 and FGF20 genes. These facts indicate that FGF16, FGF18 and FGF20 are pharmacogenomics targets in the field of oncology and regenerative medicine.

Endocardial and epicardial derived FGF signals regulate myocardial proliferation and differentiation in vivo

The epicardium regulates growth and survival of the underlying myocardium. This activity depends on intrinsic retinoic acid (RA) and erythropoietin signals. However, these signals do not act directly on the myocardium and instead are proposed to regulate the production of an unidentified soluble epicardial derived mitogen. Here, we show that Fgf9, Fgf16, and Fgf20 are expressed in the endocardium and epicardium and that RA can induce epicardial expression of Fgf9. Using knockout mice and an embryonic heart organ culture system, we show that endocardial and epicardial derived FGF signals regulate myocardial proliferation during midgestation heart development. We further show that this FGF signal is received by both FGF receptors 1 and 2 acting redundantly in the cardiomyoblast. In the absence of this signal, premature differentiation results in cellular hypertrophy and newborn mice develop a dilated cardiomyopathy. FGFs thus constitute all or part of the epicardial signal regulating myocardial growth and differentiation.

Expression of mouse fibroblast growth factor and fibroblast growth factor receptor genes during early inner ear development

The inner ear, which mediates hearing and equilibrium, develops from an ectodermal placode located adjacent to the developing hindbrain. Induction of the placode and its subsequent morphogenesis and differentiation into the inner ear epithelium and its sensory neurons, involves signalling interactions within and between otic and non-otic tissues. Several members of the fibroblast growth factor (FGF) family play important roles at various stages of otic development; however, there are additional family members that have not been evaluated. In this study, we surveyed the expression patterns of 18 mouse Fgf and 3 Fgf receptor (Fgfr) genes during early otic development. Two members of the Fgf family, Fgf4 and Fgf16, and all three tested members of the Fgfr family, Fgfr2c, Fgfr3c, and Fgfr4, were expressed in tissues relevant to inner ear development. Fgf4 transcripts were expressed in the preplacodal and placodal ectoderm, suggesting potential roles in placode induction and/or maintenance. Fgf16 was expressed in the posterior otic cup and vesicle, suggesting roles in otic cell fate decisions and/or axis formation.

Specification of dorsal telencephalic character by sequential Wnt and FGF signaling

Dorsoventral patterning of the telencephalon is established early in forebrain development and underlies many of the regional subdivisions that are critical to the later organization of neural circuits in the cerebral cortex and basal ganglia. Sonic hedgehog (Shh) is involved in the generation of the ventral-most telencephalic cells, but the identity of the extrinsic signal(s) that induce dorsal character in telencephalic cells is not known. Here we show in chick embryos that sequential Wnt and fibroblast growth factor (FGF) signaling specifies cells of dorsal telencephalic character.

Fgf genes in the basal chordate Ciona intestinalis

In vertebrates, a number of fibroblast growth factors (FGFs) have been shown to play important roles in developing embryos and adult organisms. However, the molecular relationships of the vertebrate FGFs are not yet completely understood, partly due to the divergence of their amino acid sequences. To solve this problem, we have identified six FGF genes in a basal chordate, the ascidian Ciona intestinalis. A phylogenetic analysis confidently assigned two of them to vertebrate FGF8/17/18 and FGF11/12/13/14, respectively. Based on the presence of the conserved domains within or outside of the FGF domains, we speculate that three of the other genes are orthologous to vertebrate FGF3/7/10/22, FGF4/5/6 and FGF9/16/20, respectively, although we cannot assign the sixth member to any of the vertebrate FGFs. A survey of the raw whole genome shotgun sequences of C. intestinalis demonstrated the presence of no FGF genes other than the six genes in the genome. The identification of these six FGF genes in the basal chordate gave us an insight into the diversification of specific subfamilies of vertebrate FGFs.

Fibroblast growth factors and their receptors in oligodendrocyte development: implications for demyelination and remyelination

Fibroblast growth factors are a family of broad-spectrum growth factors influencing a plethora of cellular activities. The interaction of at least 23 ligands, 4 receptors and multiple coreceptors provides a dramatic complexity to a signaling system capable of effecting a multitude of responses. This review focuses on the fibroblast growth factors signaling in oligodendrocyte development, function and discusses implications for demyelination/remyelination.

Fibroblast growth factors in cancer: therapeutic possibilities

The fibroblast growth factor (FGF) family of signalling molecules and its receptors (FGFRs) contribute to normal developmental and physiological processes. However, the subversion of this powerful growth stimulatory pathway has been implicated in the generation of a variety of pathological conditions. This review focuses on the role of FGF/FGFRs in cancer. The case will be made that this signalling pathway is associated with and functionally important for the growth of some human tumours. As such, FGF/FGFRs can be viewed as rational therapeutic oncology targets and strategies used to inhibit these molecules are discussed. The therapeutic exploitation of tumour-associated FGFR expression to deliver toxins or antiproliferative signals to tumour cells is also reviewed, as is the use of FGFs as protein therapeutics to alleviate the side effects of cancer therapy.

Expression of the fibroblast growth factor family and their receptor family genes during mouse brain development

The fibroblast growth factor (FGF) family is composed of nine members and four genes encode protein tyrosine kinase receptors for them. To gain insight into the involvement of FGFs and their receptors in the development of nervous system, their expression in brains of perinatal and adult mice was examined by semi-quantitative reverse transcription-linked polymerase chain reactions and in situ hybridization. Although all the genes, with the exception of FGF-4, were found to be expressed, FGF-3, FGF-6, FGF-7 and FGF-8 genes demonstrated higher expression in the late embryonic stages than in postnatal stages, suggesting that these members are involved in the late stages of brain development. In contrast, expression of FGF-1 and FGF-5 increased after birth. Interestingly, FGF-6 expression in perinatal mice was restricted to the central nervous system and skeltal muscles, with intense signals in the developing cerebrum in embryos but in cerebellum in 5-day-old neonates. Furthermore, FGF-receptor (FGFR)-4, a cognate receptor for FGF-6, demonstrated similar spatiotemporal expression, suggesting that FGF-6 and FGFR-4 plays significant roles in the maturation of nervous system as a ligand-receptor system. The results indicate that individual member of the fibroblast growth factor and their receptor family are expressed either sequentially or simultaneously in brain development, strongly suggesting their involvement in the regulation of a variety of developmental processes of brain, i.e., proliferation and migration of neuronal progenitor cells, neuron and glia differentiation, neurite extensions, and synapse formations.

Differentially expressed fibroblast growth factors regulate skeletal muscle development through autocrine and paracrine mechanisms

Several FGF family members are expressed in skeletal muscle; however, the roles of these factors in skeletal muscle development are unclear. We examined the RNA expression, protein levels, and biological activities of the FGF family in the MM14 mouse skeletal muscle cell line. Proliferating skeletal muscle cells express FGF-1, FGF-2, FGF-6, and FGF-7 mRNA. Differentiated myofibers express FGF-5, FGF-7, and reduced levels of FGF-6 mRNA. FGF-3, FGF-4, and FGF-8 were not detectable by RT-PCR in either proliferating or differentiated skeletal muscle cells. FGF-I and FGF-2 proteins were present in proliferating skeletal muscle cells, but undetectable after terminal differentiation. We show that transfection of expression constructs encoding FGF-1 or FGF-2 mimics the effects of exogenously applied FGFs, inhibiting skeletal muscle cell differentiation and stimulating DNA synthesis. These effects require activation of an FGF tyrosine kinase receptor as they are blocked by transfection of a dominant negative mutant FGF receptor. Transient transfection of cells with FGF-1 or FGF-2 expression constructs exerted a global effect on myoblast DNA synthesis, as greater than 50% of the nontransfected cells responded by initiating DNA synthesis. The global effect of cultures transfected with FGF-2 expression vectors was blocked by an anti-FGF-2 monoclonal antibody, suggesting that FGF-2 was exported from the transfected cells. Despite the fact that both FGF-l and FGF-2 lack secretory signal sequences, when expressed intracellularly, they regulate skeletal muscle development. Thus, production of FGF-1 and FGF-2 by skeletal muscle cells may act as a paracrine and autocrine regulator of skeletal muscle development in vivo.

Expression of FGF-2 and FGF receptor type 1 in the adult rat brainstem: effect of colchicine

In the adult rat brainstem, neuronal subpopulations of several motor and sensory nuclei display basic fibroblast growth factor (bFGF or FGF-2) immunoreactivity (IR; Grothe et al. J. Comp. Neurol. 305:328-336). In the present study we demonstrate that FGF-2-IR correlates with staining for the high-affinity FGF-receptor 1. Intracerebroventricular injection of colchicine leads to the disappearance or substantial reduction of FGF-2-IR in the hypoglossal, facial, trigeminal motor, trochlear, and mesencephalic trigeminal nuclei. In contrast, FGF-2-IR appears in many perikarya of the red nucleus and the medial nucleus of the trapezoid body, whereas in control rats both nuclei showed immunostained fibers and almost no immunoreactive cell bodies. This dramatic change of FGF-2-IR could be explained by the ability of colchicine to block fast axonal transport. Cranial nuclei may internalize FGF-2 at the periphery via high-affinity receptors and retrogradely transport the molecule to their perikarya. The red nucleus and the medial nucleus of the trapezoid body may synthesize FGF-2 and provide the growth factor to afferent or efferent neurons. The presence of FGF-2 mRNA in brainstem extract and the absence of the FGF-2 transcript in extracts of the hypoglossal nucleus corroborate this suggestion. The effect of colchicine on FGF-2-IR in the brainstem nuclei suggests that FGF-2 could be specifically retrogradely transported in other cranial nuclei, in addition to the hypoglossal system. Together with the ability of FGF-2 to stimulate neuronal survival, this result strongly supports the hypothesis that FGF-2 is acting as a neurotrophic factor on specific central neuron populations.

Novel expression of the tyrosine hydroxylase gene requires both acidic fibroblast growth factor and an activator

Substances found in the soluble extract of muscle can alter the differentiative fate of certain brain neurons in culture by triggering novel expression of the gene for the catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) (Iacovitti et al., 1989; Iacovitt, 1991). In this study, we demonstrate that TH induction in cultured noncatecholamine neurons from the mouse striatum requires the cooperative interaction of at least two substances found in muscle. Purification studies, combined with biological assay, revealed that one necessary component is acidic fibroblast growth factor (aFGF), and the other, an unidentified molecule(s) of < 10 kDa molecular weight that activated aFGF. Thus, muscle-derived aFGF, if incubated in the presence but not the absence of the < 10 kDa fraction of muscle, induced a dose-dependent increase in the number of striatal neurons that novelly express TH. This expression was blocked by prior incubation and protein A precipitation of the factor with polyclonal antibodies to aFGF (1:200-1:1000). Similar to muscle-purified aFGF, commercial preparations of native bovine and human recombinant aFGF (0.1-100 ng/ml) were potent inducers of TH when coincubated with the < 10 kDa activator. In contrast, basic FGF produced little and FGF-7 no induction of TH. Unlike the unidentified activating agent in muscle, heparin (20-500 mU), a known activator of aFGF, did not potentiate the factor's TH-inducing activity. Nonetheless, heparatinase (100 mU) prevented TH induction by aFGF and its activator, indicating that binding of heparan sulfated proteoglycans is necessary for the effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear and cytoplasmic localization of different basic fibroblast growth factor species

The subcellular distribution of basic fibroblastic growth factor (bFGF) was analyzed by subcellular fractionation and immunofluorescence to gain insight into potential mechanisms for its release from cells. Subcellular fractionation of either SK-Hep-1 cells or NIH 3T3 cells transfected with a bFGF cDNA revealed that the 18 kd form of bFGF was found primarily in the cytosolic fraction, whereas the 22 and 24 kd forms of bFGF were found preferentially in ribosomal and nuclear fractions. Analysis of bFGF distribution by immunofluorescence using an antibody that recognized all forms of bFGF indicated both cytoplasmic and nuclear localization but failed to reveal any growth factor in structures representing secretory vesicles. Therefore, bFGF has a distribution inconsistent with that of a secretory protein.

Evidence that fibroblast growth factor promotes lens fibre differentiation

Lens epithelial cells from newborn rats undergo changes characteristic of fibre differentiation when cultured with rat neural retina or with a soluble mitogenic factor present in calf retina-conditioned medium. Mitogens have been isolated from retina in other laboratories, but have not previously been shown to promote fibre differentiation in mammalian lens. We prepared eye-derived growth factors I and II and alpha- and beta-retina-derived growth factors from bovine retinas. These factors all promoted lens fibre differentiation in our culture system, as assessed by morphological changes and the appearance of fibre cell-specific crystallins. There is now strong evidence that these retina-derived factors are identical to the acidic and basic forms of fibroblast growth factor (FGF), which is present in a variety of tissues. We found that acidic and basic FGF from rat brain also promoted lens fibre differentiation, suggesting that FGF is the factor from the retina responsible for inducing lens fibre differentiation.