FGF8, FGF10 and FGF receptor 2 in foreskin of children with hypospadias: an analysis of immunohistochemical expression patterns and gene transcription.

INTRODUCTION: Fibroblast growth factors (FGFs) play a crucial role in early embryogenesis of the genital tubercle and are involved in the development of hypospadias, affecting both endo- and ectodermally derived tissues. It was hypothesized that expression of FGFs could be qualitatively or quantitatively altered in skin of children with hypospadias. OBJECTIVE: The objective of the study was to investigate expression patterns and transcription levels of FGF8, FGF10, and FGF Receptor 2 (FGFR2) in patients with hypospadias compared to normal controls. PATIENTS AND METHODS: Skin samples from the ventro-lateral aspect of the foreskin of 32 patients with hypospadias (17 distal and 15 proximal, mean age 25 months) and 10 normal foreskin samples (mean age 77 months) were analyzed by immunohistochemistry. Staining, localization, and distribution of positive cells in epidermis and dermis were categorized independently by two researchers. Complementary DNA (cDNA) samples prepared from messenger RNA (mRNA) isolates of the same samples were analyzed by quantitative polymerase chain reaction (qPCR), comparing expressions of FGF8, FGF10, and FGFR2 with loading controls. RESULTS: Patients with hypospadias consistently showed aberrant immunohistochemical staining patterns for FGF8/FGF10/FGFR2 in epidermis and dermis compared to patients without penile malformation (p < 0.01 for all markers). qPCR displayed no difference in expression levels on mRNA level (FGFR2 p = 0.44, FGF8 p = 0.77, and FGF10 p = 0.17) comparing normal foreskin with foreskin from patients with hypospadias. Figure. DISCUSSION: The results point at an impact of FGF signaling during embryological development of hypospadias on skin, as an ectodermally derived tissue. Similar to the urethral development, this might be a result of mesothelial-epithelial interactions. The differing expression patterns in immunohistochemistry are not matched by a quantitative difference in marker expression on the mRNA level, putatively caused by post-translational modifications or alterations of the downstream pathway. FGFs, particularly FGF10 and FGFR2, are critically involved in wound healing. CONCLUSIONS: There are significant differences in localization and distribution of FGF8, FGF10, and FGFR2 in comparisons of normal foreskin to foreskin of patients with hypospadias, whereas there is no difference in the quantitative expression of these markers on the mRNA level. This confirms the notion that penile skin is affected as well by the embryological aberrations during the embryogenesis of hypospadias.

Sonic hedgehog protein regulates fibroblast growth factor 8 expression in metanephric explant culture from BALB/c mice: Possible mechanisms associated with renal morphogenesis.

The sonic hedgehog (SHH) morphogen regulates cell differentiation and controls a number of genes during renal morphogenesis. To date, the effects of SHH on fibroblast growth factors (Fgfs) in embryonic kidney development remain unclear. In the present study, explants of BALB/c mouse embryonic kidney tissues were used to investigate the role of exogenous SHH on Fgf8 and Fgf10 expression levels ex vivo. Ureteric bud branches and epithelial metanephric derivatives were used to determine the renal morphogenesis with Dolichos biflorus agglutinin or hematoxylin­eosin staining. mRNA expression levels were determined using reverse transcription­quantitative polymerase chain reaction, while the protein expression levels were examined using immunohistochemistry and western blot analysis. During the initial stages of metanephric development, low levels of SHH, Fgf8, and Fgf10 expression were observed, which were found to increase significantly during more advanced stages of metanephric development. In addition, exogenous SHH protein treatment increased the number of ureteric bud branches and enhanced the formation of nephrons. Exogenous SHH reduced the Fgf8 mRNA and protein expression levels, whereas cyclopamine (an SHH­smoothened receptor inhibitor) interfered with SHH­mediated downregulation of Fgf8 expression. By contrast, exogenous SHH protein was not found to modulate Fgf10 mRNA and protein expression levels. In conclusion, these results indicate that the modulatory effects of SHH on BALB/c mouse metanephric explant cultures may involve the regulation of Fgf8 expression but not Fgf10 expression, which provides evidence for the functional role of Fgf proteins in renal morphogenesis.

Endocytosis of Fgf8 is a double-stage process and regulates spreading and signaling.

Tightly controlled concentration gradients of morphogens provide positional information and thus regulate tissue differentiation and morphogenesis in multicellular organisms. However, how such morphogenetic fields are formed and maintained remains debated. Here we show that fibroblast growth factor 8 (Fgf8) morphogen gradients in zebrafish embryos are established and maintained by two essential mechanisms. Firstly, Fgf8 is taken up into the cell by clathrin-mediated endocytosis. The speed of the uptake rate defines the range of the morphogenetic gradient of Fgf8. Secondly, our data demonstrate that after endocytosis the routing of Fgf8 from the early endosome to the late endosome shuts down signaling. Therefore, intracellular endocytic transport regulates the intensity and duration of Fgf8 signaling. We show that internalization of Fgf8 into the early endosome and subsequent transport towards the late endosome are two independent processes. Therefore, we hypothesize that Fgf8 receiving cells control both, the propagation width and the signal strength of the morphogen.

The similarity between human embryonic stem cell-derived epithelial cells and ameloblast-lineage cells.

This study aimed to compare epithelial cells derived from human embryonic stem cells (hESCs) to human ameloblast-lineage cells (ALCs), as a way to determine their potential use as a cell source for ameloblast regeneration. Induced by various concentrations of bone morphogenetic protein 4 (BMP4), retinoic acid (RA) and lithium chloride (LiCl) for 7 days, hESCs adopted cobble-stone epithelial phenotype (hESC-derived epithelial cells (ES-ECs)) and expressed cytokeratin 14. Compared with ALCs and oral epithelial cells (OE), ES-ECs expressed amelogenesis-associated genes similar to ALCs. ES-ECs were compared with human fetal skin epithelium, human fetal oral buccal mucosal epithelial cells and human ALCs for their expression pattern of cytokeratins as well. ALCs had relatively high expression levels of cytokeratin 76, which was also found to be upregulated in ES-ECs. Based on the present study, with the similarity of gene expression with ALCs, ES-ECs are a promising potential cell source for regeneration, which are not available in erupted human teeth for regeneration of enamel.

Wnt/beta-catenin signaling has an essential role in the initiation of limb regeneration.

Anuran (frog) tadpoles and urodeles (newts and salamanders) are the only vertebrates capable of fully regenerating amputated limbs. During the early stages of regeneration these amphibians form a "blastema", a group of mesenchymal progenitor cells that specifically directs the regrowth of the limb. We report that wnt-3a is expressed in the apical epithelium of regenerating Xenopus laevis limb buds, at the appropriate time and place to play a role during blastema formation. To test whether Wnt/beta-catenin signaling is required for limb regeneration, we created transgenic X. laevis tadpoles that express Dickkopf-1 (Dkk1), a specific inhibitor of Wnt/beta-catenin signaling, under the control of a heat-shock promoter. Heat-shock immediately before limb amputation or during early blastema formation blocked limb regeneration but did not affect the development of contralateral, un-amputated limb buds. When the transgenic tadpoles were heat-shocked following the formation of a blastema, however, they retained the ability to regenerate partial hindlimb structures. Furthermore, heat-shock induced Dkk1 blocked fgf-8 but not fgf-10 expression in the blastema. We conclude that Wnt/beta-catenin signaling has an essential role during the early stages of limb regeneration, but is not absolutely required after blastema formation.

NF-kappaB activation upregulates fibroblast growth factor 8 expression in prostate cancer cells.

BACKGROUND: Fibroblast growth factor 8 (FGF8) is over-expressed in prostate cancer (CaP) correlating with high-grade disease and reduced survival. The role of acetylation in transcriptional regulation of FGF8 was investigated using the histone deacetylase (HDAC) inhibitor Trichostatin A (TSA). METHODS: FGF8 transcriptional response to TSA was investigated by gene reporter assays, RT-PCR, and Western blotting. Chromatin immunoprecipitation (ChIP) assays were also performed. RESULTS: FGF8 is upregulated in response to TSA treatment along with NF-kappaB transcriptional activity. Over-expression of p65 activated FGF8 transcription. ChIP assays revealed p65 recruitment to the fgf8 promoter, containing putative NF-kappaB binding sites, post TSA stimulation. PI-3K activity is required for TSA mediated FGF8 upregulation. CONCLUSION: Using TSA treatment in prostate cancer cells, a requirement of PI-3K activity in mediating TSA function is demonstrated and a novel role for NF-kappaB in the regulation of FGF8 expression is uncovered.

Development of midline cell types and commissural axon tracts requires Fgfr1 in the cerebrum.

The adult cerebral hemispheres are connected to each other by specialized midline cell types and by three axonal tracts: the corpus callosum, the hippocampal commissure, and the anterior commissure. Many steps are required for these tracts to form, including early patterning and later axon pathfinding steps. Here, the requirement for FGF signaling in forming midline cell types and commissural axon tracts of the cerebral hemispheres is examined. Fgfr1, but not Fgfr3, is found to be essential for establishing all three commissural tracts. In an Fgfr1 mutant, commissural neurons are present and initially project their axons, but these fail to cross the midline that separates the hemispheres. Moreover, midline patterning defects are observed in the mutant. These defects include the loss of the septum and three specialized glial cell types, the indusium griseum glia, midline zipper glia, and glial wedge. Our findings demonstrate that FGF signaling is required for generating telencephalic midline structures, in particular septal and glial cell types and all three cerebral commissures. In addition, analysis of the Fgfr1 heterozygous mutant, in which midline patterning is normal but commissural defects still occur, suggests that at least two distinct FGF-dependent mechanisms underlie the formation of the cerebral commissures.