Fgf22 and Fgfr2b are required for neurogenesis and gliogenesis in the zebrafish forebrain.

Fibroblast growth factors (Fgfs) play crucial roles in various developmental processes including brain development. We previously identified Fgf22 in zebrafish and found that fgf22 is involved in midbrain patterning during embryogenesis. Here, we investigated the role of Fgf22 in the formation of the zebrafish forebrain. We found that fgf22 was essential for determining the ventral properties of the telencephalon and diencephalon but not for cell proliferation. In addition, the knockdown of fgf22 inhibited the generation of glutamatergic neurons, γ-aminobutyric acid (GABA)ergic interneurons and astrocytes. Recently, Fgf signaling has received much attention because of its importance in the pathogenesis of multiple sclerosis, in which oligodendrocytes and myelin are destroyed. However, the effects of each Fgf on oligodendrocytes remain largely unknown. Therefore, we also investigated the role of Fgf22 in oligodendrocyte development and explored whether there is a difference between Fgf22 and other Fgfs. Knockdown of fgf22 promoted the generation of oligodendrocytes. Conversely, overexpression of fgf22 inhibited the generation of oligodendrocytes. Furthermore, the forebrain phenotypes of fgfr2b knockdown zebrafish were remarkably similar to those of fgf22 knockdown zebrafish. This establishes the Fgf22-Fgfr2b axis as a key ligand‒receptor partnership in neurogenesis and gliogenesis in the forebrain. Our results indicate that Fgf22 has a unique function in suppressing oligodendrocyte differentiation through Fgfr2b without affecting cell proliferation.

Expression of Fgf23 in activated dendritic cells and macrophages in response to immunological stimuli in mice.

Fibroblast growth factors (Fgfs) are polypeptide growth factors with diverse biological activities. While several studies have revealed that Fgf23 plays important roles in the regulation of phosphate and vitamin D metabolism, the additional physiological roles of Fgf23 remain unclear. Although it is believed that osteoblasts/osteocytes are the main sources of Fgf23, we previously found that Fgf23 mRNA is also expressed in the mouse thymus, suggesting that it might be involved in the immune system. In this study we examined the potential roles of Fgf23 in immunological responses. Mouse serum Fgf23 levels were significantly increased following inoculation with Escherichia coli or Staphylococcus aureus or intraperitoneal injection of lipopolysaccharide. We also identified activated dendritic cells and macrophages that potentially contributed to increased serum Fgf23 levels. Nuclear factor-kappa B (NF-κB) signaling was essential for the induction of Fgf23 expression in dendritic cells in response to immunological stimuli. Moreover, we examined the effects of recombinant Fgf23 protein on immune cells in vitro. Fgfr1c, a potential receptor for Fgf23, was abundantly expressed in macrophages, suggesting that Fgf23 might be involved in signal transduction in these cells. Our data suggest that Fgf23 potentially increases the number in macrophages and induces expression of tumor necrosis factor-α (TNF-α), a proinflammatory cytokine. Collectively, these data suggest that Fgf23 might be intimately involved in inflammatory processes.

A putative polypeptide N-acetylgalactosaminyltransferase/Williams-Beuren syndrome chromosome region 17 (WBSCR17) regulates lamellipodium formation and macropinocytosis.

We previously identified a novel polypeptide N-acetylgalactosaminyltransferase (GalNAc-T) gene, which is designated Williams-Beuren syndrome chromosome region 17 (WBSCR17) because it is located in the chromosomal flanking region of the Williams-Beuren syndrome deletion. Recent genome-scale analysis of HEK293T cells treated with a high concentration of N-acetylglucosamine (GlcNAc) demonstrated that WBSCR17 was one of the up-regulated genes possibly involved in endocytosis (Lau, K. S., Khan, S., and Dennis, J. W. (2008) Genome-scale identification of UDP-GlcNAc-dependent pathways. Proteomics 8, 3294-3302). To assess its roles, we first expressed recombinant WBSCR17 in COS7 cells and demonstrated that it was N-glycosylated and localized mainly in the Golgi apparatus, as is the case for the other GalNAc-Ts. Assay of recombinant WBSCR17 expressed in insect cells showed very low activity toward typical mucin peptide substrates. We then suppressed the expression of endogenous WBSCR17 in HEK293T cells using siRNAs and observed phenotypic changes of the knockdown cells with reduced lamellipodium formation, altered O-glycan profiles, and unusual accumulation of glycoconjugates in the late endosomes/lysosomes. Analyses of endocytic pathways revealed that macropinocytosis, but neither clathrin- nor caveolin-dependent endocytosis, was elevated in the knockdown cells. This was further supported by the findings that the overexpression of recombinant WBSCR17 stimulated lamellipodium formation, altered O-glycosylation, and inhibited macropinocytosis. WBSCR17 therefore plays important roles in lamellipodium formation and the regulation of macropinocytosis as well as lysosomes. Our study suggests that a subset of O-glycosylation produced by WBSCR17 controls dynamic membrane trafficking, probably between the cell surface and the late endosomes through macropinocytosis, in response to the nutrient concentration as exemplified by environmental GlcNAc.

Oral administration of soluble ß-glucans extracted from Grifola frondosa induces systemic antitumor immune response and decreases immunosuppression in tumor-bearing mice.

Maitake D (MD)-Fraction is a highly purified soluble ß-glucan derived from Grifola frondosa (an oriental edible mushroom). Intraperitoneal (i.p.) injection of MD-Fraction has been reported to inhibit tumor growth via enhancement of the host immune system. In this study, we demonstrated that oral administration of MD-Fraction as well as i.p. injection significantly inhibited tumor growth in murine tumor models. After oral administration, MD-Fraction was not transferred to the blood in its free form but was captured by antigen-presenting cells such as macrophages and dendritic cells (DCs) present in the Peyer's patch. The captured MD-Fraction was then transported to the spleen, thereby inducing the systemic immune response. Our study showed that MD-Fraction directly induced DC maturation via a C-type lectin receptor dectin-1 pathway. The therapeutic response of orally administered MD-Fraction was associated with (i) induced systemic tumor-antigen specific T cell response via dectin-1-dependent activation of DCs, (ii) increased infiltration of the activated T cells into the tumor and (iii) decreased number of tumor-caused immunosuppressive cells such as regulatory T cells and myeloid-derived suppressor cells. Our preclinical study suggests that MD-Fraction is a useful oral therapeutic agent in the management of patients with cancer.

Fgf20b is required for the ectomesenchymal fate establishment of cranial neural crest cells in zebrafish.

In cranial skeletal development, the establishment of the ectomesenchymal lineage within the cranial neural crest is of great significance. Fgfs are polypeptide growth factors with diverse functions in development and metabolism. Fgf20b knockdown zebrafish embryos showed dysplastic neurocranial and pharyngeal cartilages. Ectomesenchymal cells from cranial neural crest cells were significantly decreased in Fgf20b knockdown embryos, but cranial neural crest cells with a non-ectomesnchymal fate were increased. However, the proliferation and apoptosis of cranial neural crest cells were essentially unchanged. Fgfr1 knockdown embryos also showed dysplastic neurocranial and pharyngeal cartilages. The present findings indicate that Fgf20b is required for ectomesenchymal fate establishment via the activation of Fgfr1 in zebrafish.

Fgf4 is required for left-right patterning of visceral organs in zebrafish.

Fgf signaling plays essential roles in many developmental events. To investigate the roles of Fgf4 signaling in zebrafish development, we generated Fgf4 knockdown embryos by injection with Fgf4 antisense morpholino oligonucleotides. Randomized LR patterning of visceral organs including the liver, pancreas, and heart was observed in the knockdown embryos. Prominent expression of Fgf4 was observed in the posterior notochord and Kupffer's vesicle region in the early stages of segmentation. Lefty1, lefty2, southpaw, and pitx2 are known to play crucial roles in LR patterning of visceral organs. Fgf4 was essential for the expression of lefty1, which is necessary for the asymmetric expression of southpaw and pitx2 in the lateral plate mesoderm, in the posterior notochord, and the expression of lefty2 and lefty1 in the left cardiac field. Fgf8 is also known to be crucial for the formation of Kupffer's vesicle, which is needed for the LR patterning of visceral organs. In contrast, Fgf4 was required for the formation of cilia in Kupffer's vesicle, indicating that the role of Fgf4 in the LR patterning is quite distinct from that of Fgf8. The present findings indicate that Fgf4 plays a unique role in the LR patterning of visceral organs in zebrafish.

Chondroitin 4-O-sulfotransferase-1 is required for somitic muscle development and motor axon guidance in zebrafish.

CS (chondroitin sulfate) has been implicated in a variety of biological processes during development. Its biological functions are closely associated with characteristic sulfated structures. Here, we report the characterization of a zebrafish counterpart of C4ST-1 (chondroitin 4-O-sulfotransferase-1) and its functional importance in embryogenesis. Recombinant C4ST-1 showed a substrate preference for chondroitin and catalysed the 4-O-sulfation of GalNAc residues, a highly frequent modification of CS in the embryos of zebrafish as well as other vertebrates. Whole-mount in situ hybridization revealed that C4ST-1 showed a distinct spatiotemporal expression pattern in the developing zebrafish embryo. During the segmentation stages, strong expression was observed along the body axis including the notochord and somites. Functional knockdown of C4ST-1 with specific antisense morpholino-oligonucleotides led to a marked decrease in the 4-O-sulfation and amount of CS in the embryos. Consistent with the preferential expression in the rostrocaudal axis, C4ST-1 morphants displayed morphological defects exemplified by a ventrally bent trunk and a curled and/or kinky tail, largely due to misregulated myotomal myod expression, implying perturbation of axial muscle differentiation in somites. Furthermore, the aberrant projection of spinal motor axons, which extended ventrally at the interface between the notochord and individual somites, was also observed in C4ST-1 morphants. These results suggest that 4-O-sulfated CS formed by C4ST-1 is essential for somitic muscle differentiation and motor axon guidance in zebrafish development.

Fgf19 is required for zebrafish lens and retina development.

Fgf signaling plays crucial roles in morphogenesis. Fgf19 is required for zebrafish forebrain development. Here, we examined the roles of Fgf19 in the formation of the lens and retina in zebrafish. Knockdown of Fgf19 caused a size reduction of the lens and the retina, failure of closure of the choroids fissure, and a progressive expansion of the retinal tissue to the midline of the forebrain. Fgf19 expressed in the nasal retina and lens was involved in cell survival but not cell proliferation during embryonic lens and retina development. Fgf19 was essential for the differentiation of lens fiber cells in the lens but not for the neuronal differentiation and lamination in the retina. Loss of nasal fate in the retina caused by the knockdown of Fgf19, expansion of nasal fate in the retina caused by the overexpression of Fgf19 and eye transplantation indicated that Fgf19 in the retina was crucial for the nasal-temporal patterning of the retina that is critical for the guidance of retinal ganglion cell axons. Knockdown of Fgf19 also caused incorrect axon pathfinding. The present findings indicate that Fgf19 positively regulates the patterning and growth of the retina, and the differentiation and growth of the lens in zebrafish.

Neucrin is a novel neural-specific secreted antagonist to canonical Wnt signaling.

A gene encoding a novel secreted protein in mice and humans was identified, and named Neucrin. Mouse Neucrin consists of 343 amino acids with a cysteine-rich domain in its carboxyl terminal region. The positions of 10 cysteine residues in the cysteine-rich domain are similar to those of Dickkopfs (Dkks), secreted Wnt antagonists. However, whereas Dkks have two cysteine-rich domains, Neucrin has only one. Neucrin as well as Dkks bound to LDL receptor-related protein 6 and inhibited the stabilization of cytosolic beta-catenin, indicating that Neucrin is an antagonist of canonical Wnt signaling. Mouse Neucrin expression was not detected in any major tissues in the adult, but was detected in developing neural tissues, including the brain and spinal cord. The expression pattern of Neucrin is distinct from that of any Dkk. Neucrin is a unique secreted Wnt antagonist that is predominantly expressed in developing neural tissues.

ATPase activity and its temperature compensation of the cyanobacterial clock protein KaiC.

KaiA, KaiB and KaiC constitute the circadian clock machinery in cyanobacteria. KaiC is a homohexamer; its subunit contains duplicated halves, each with a set of ATPase motifs. Here, using highly purified KaiC preparations of the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 produced in Escherichia coli, we found that the N- and C-terminal domains of KaiC had extremely weak ATPase activity. ATPase activity showed temperature compensation in wild-type KaiC, but not in KaiC(S431A/T432A), a mutant that lacks two phosphorylation sites. We concluded that KaiC phosphorylation is involved in the ATPase temperature-compensation mechanism-which is probably critical to the stability of the circadian clock in cyanobacteria-and we hypothesized the following temperature-compensation mechanism: (i) The C-terminal phosphorylation sites of a KaiC hexamer subunit are phosphorylated by the C-terminal domain of an adjacent KaiC subunit; (ii) the phosphorylation suppresses the ATPase activity of the C-terminal domain; and (iii) the phosphorylated KaiC spontaneously dephosphorylates, resulting in the recover of ATPase activity.

The Relationship between Uterine, Fecal, Bedding, and Airborne Dust Microbiota from Dairy Cows and Their Environment: A Pilot Study.

The aim of this study was to characterize uterine, fecal, bedding, and airborne dust microbiota from postpartum dairy cows and their environment. The cows were managed by the free-stall housing system, and samples for microbiota and serum metabolite assessment were collected during summer and winter when the cows were at one and two months postpartum. Uterine microbiota varied between seasons; the five most prevalent taxa were Enterobacteriaceae, Moraxellaceae, Ruminococcaceae, Staphylococcaceae, and Lactobacillaceae during summer, and Ruminococcaceae, Lachnospiraceae, Bacteroidaceae, Moraxellaceae, and Clostridiaceae during winter. Although Actinomycetaceae and Mycoplasmataceae were detected at high abundance in several uterine samples, the relationship between the uterine microbiota and serum metabolite concentrations was unclear. The fecal microbiota was stable regardless of the season, whereas bedding and airborne dust microbiota varied between summer and winter. With regards to uterine, bedding, and airborne dust microbiota, Enterobacteriaceae, Moraxellaceae, Staphylococcaceae, and Lactobacillaceae were more abundant during summer, and Ruminococcaceae, Lachnospiraceae, Bacteroidaceae, and Clostridiaceae were more abundant during winter. Canonical analysis of principal coordinates confirmed the relationship between uterine and cowshed microbiota. These results indicated that the uterine microbiota may vary when the microbiota in cowshed environments changes.

Brorin is required for neurogenesis, gliogenesis, and commissural axon guidance in the zebrafish forebrain.

Bmps regulate numerous neural functions with their regulators. We previously identified Brorin, a neural-specific secreted antagonist of Bmp signaling, in humans, mice, and zebrafish. Mouse Brorin has two cysteine-rich domains containing 10 cysteine residues in its core region, and these are located in similar positions to those in the cysteine-rich domains of Chordin family members, which are secreted Bmp antagonists. Zebrafish Brorin had two cysteine-rich domains with high similarity to those of mouse Brorin. We herein examined zebrafish brorin in order to elucidate its in vivo actions. Zebrafish brorin was predominantly expressed in developing neural tissues. The overexpression of brorin led to the inactivation of Bmp signaling. On the other hand, the knockdown of brorin resulted in the activation of Bmp signaling and brorin morphants exhibited defective development of the ventral domain in the forebrain. Furthermore, the knockdown of brorin inhibited the generation of γ-aminobutyric acid (GABA)ergic interneurons and oligodendrocytes and promoted the generation of astrocytes in the forebrain. In addition, brorin was required for axon guidance in the forebrain. The present results suggest that Brorin is a secreted Bmp antagonist predominantly expressed in developing neural tissues and that it plays multiple roles in the development of the zebrafish forebrain.

Fgf21 regulates T-cell development in the neonatal and juvenile thymus.

We have previously shown that Fibroblast growth factor 21 (Fgf21) is expressed in the thymus as well as in the liver. In line with this expression profile, Fgf21 was recently reported to protect against ageing-related thymic senescence by improving the function of thymic epithelial cells (TECs). However, the function of Fgf21 in the juvenile thymus remained to be elucidated. We investigated the physiological roles of Fgf21 in the juvenile thymus and found that young Fgf21 knockout mice, but not ß-Klotho knockout mice nor adult Fgf21 knockout mice, showed a significant reduction in the percentage of single-positive CD4+ and CD8+ thymocytes without obvious alteration in TECs. Furthermore, treatment with recombinant FGF21 protein rescued the impairment in fetal thymus organ culture (FTOC) of Fgf21 knockout mice. Annexin V staining revealed FGF21 protein enhanced apoptosis of immature thymocytes undergoing selection process in FTOC, suggesting that FGF21 may facilitate the selection of developing T cells. Endocrine Fgf21 from the liver induced by metabolic stimulation did not affect juvenile thymocyte development. Our data suggest that Fgf21 acts as one of intrathymic cytokines in the neonatal and juvenile thymus, involving thymocyte development in a ß-Klotho-independent manner.

Role of Fgf10 in cell proliferation in white adipose tissue.

The development of white adipose tissue (WAT) involves adipogenesis and cell proliferation. Although the adipogenesis has been well studied, the cell proliferation has not. Therefore, we examined the mechanism of the proliferation by analyzing Fgf10(-/-) mouse embryonic WAT, in which adipogenesis and proliferation were severely impaired. D-type cyclin expression and retinoblastoma family protein phosphorylation essential for cell proliferation were examined in WAT. Both cyclin D2 expression and p130 phosphorylation were impaired in the Fgf10(-/-) WAT. In mouse embryonic fibroblasts, Fgf10 stimulated cyclin D2 expression and p130 phosphorylation, which were inhibited by an inhibitor of the Ras/MAPK pathway. These results suggest that Fgf10 stimulates cell proliferation in WAT through the Ras/MAPK pathway followed by the cyclin D2-dependent phosphorylation of p130. In contrast, expression but not phosphorylation of pRb was impaired in the Fgf10(-/-) WAT. As pRb is essential for adipogenesis, Fgf10 might play a role in adipogenesis by inducing its expression.

Roles of fibroblast growth factor 10 (Fgf10) in adipogenesis in vivo.

The development of white adipose tissue (WAT) of Fgf10-/- mouse embryos was greatly impaired. Here, we examined the mechanism of Fgf10 action in adipogenesis in vivo. The proliferative activity in the WAT of Fgf10-/- embryos was greatly decreased. We also examined the expression of transcription factors, C/EBPbeta, C/EBPalpha and PPARgamma, that are important for adipogenesis. Although the expression of C/EBPbeta and PPARgamma in the WAT of Fgf10-/- embryos was greatly decreased, the expression of C/EBPalpha was essentially unchanged. Therefore, we examined their expression in the WAT of C/EBPalpha-/- embryos. Although the expression of C/EBPbeta and PPARgamma in the WAT was greatly decreased, the expression of Fgf10 was essentially unchanged. As these results in vivo appeared to be contradictory to a transcriptional cascade model in vitro that C/EBPbeta induces the expression of PPARgamma and C/EBPalpha reported, we also examined their expression in the WAT of wild type embryos at different developmental stages. The expression of Fgf10 and C/EBPalpha was followed by that of C/EBPbeta and PPARgamma. The present findings indicate that Fgf10 but not C/EBPalpha is required for the proliferation of preadipocytes. In contrast, both Fgf10 and C/EBPalpha acting synergistically in separate, parallel pathways are required for the differentiation. Unexpectedly, the transcriptional cascade of adipogenesis in vivo described here is distinct from the cascade in vitro previously reported.

Retinal stem/progenitor cells in the ciliary marginal zone complete retinal regeneration: a study of retinal regeneration in a novel animal model.

Our research group has extensively studied retinal regeneration in adult Xenopus laevis. However, X. laevis does not represent a suitable model for multigenerational genetics and genomic approaches. Instead, Xenopus tropicalis is considered as the ideal model for these studies, although little is known about retinal regeneration in X. tropicalis. In the present study, we showed that a complete retina regenerates at approximately 30 days after whole retinal removal. The regenerating retina was derived from the stem/progenitor cells in the ciliary marginal zone (CMZ), indicating a novel mode of vertebrate retinal regeneration, which has not been previously reported. In a previous study, we showed that in X. laevis, retinal regeneration occurs primarily through the transdifferentiation of retinal pigmented epithelial (RPE) cells. RPE cells migrate to the retinal vascular membrane and reform a new epithelium, which then differentiates into the retina. In X. tropicalis, RPE cells also migrated to the vascular membrane, but transdifferentiation was not evident. Using two tissue culture models of RPE tissues, it was shown that in X. laevis RPE culture neuronal differentiation and reconstruction of the retinal three-dimensional (3-D) structure were clearly observed, while in X. tropicalis RPE culture neither ßIII tubulin-positive cells nor 3-D retinal structure were seen. These results indicate that the two Xenopus species are excellent models to clarify the cellular and molecular mechanisms of retinal regeneration, as these animals have contrasting modes of regeneration; one mode primarily involves RPE cells and the other mode involves stem/progenitor cells in the CMZ.

Fgf16 is required for specification of GABAergic neurons and oligodendrocytes in the zebrafish forebrain.

Fibroblast growth factor (Fgf) signaling plays crucial roles in various developmental processes including those in the brain. We examined the role of Fgf16 in the formation of the zebrafish brain. The knockdown of fgf16 decreased cell proliferation in the forebrain and midbrain. fgf16 was also essential for development of the ventral telencephalon and diencephalon, whereas fgf16 was not required for dorsoventral patterning in the midbrain. fgf16 was additionally required for the specification and differentiation of γ-aminobutyric acid (GABA)ergic interneurons and oligodendrocytes, but not for those of glutamatergic neurons in the forebrain. Cross talk between Fgf and Hedgehog (Hh) signaling was critical for the specification of GABAergic interneurons and oligodendrocytes. The expression of fgf16 in the forebrain was down-regulated by the inhibition of Hh and Fgf19 signaling, but not by that of Fgf3/Fgf8 signaling. The fgf16 morphant phenotype was similar to that of the fgf19 morphant and embryos blocked Hh signaling. The results of the present study indicate that Fgf16 signaling, which is regulated by the downstream pathways of Hh-Fgf19 in the forebrain, is involved in forebrain development.

Identification and expression analysis of zebrafish polypeptide α-N-acetylgalactosaminyltransferase Y-subfamily genes during embryonic development.

Mucin-type glycosylation is one of the most common posttranslational modifications of secretory and membrane proteins and has diverse physiological functions. The initial biosynthesis of mucin-type carbohydrates is catalyzed by UDP-GalNAc: polypeptide α-N-acetylgalactosaminyltransferases (GalNAc-Ts) encoded by GALNT genes. Among these, GalNAc-T8, -T9, -T17, and -T18 form a characteristic subfamily called "Y-subfamily" and have no or very low in vitro transferase activities when assayed with typical mucin peptides as acceptor substrates. Although the Y-subfamily isozymes have been reported to be possibly involved in various diseases, their in vivo functions have not been reported. Here, we isolated zebrafish Y-subfamily galnt genes, and determined their spatial and temporal expressions during the early development of zebrafish. Our study demonstrated that all the Y-subfamily isozymes were well conserved in zebrafish with GalNAc-T18 having two orthologs, galnt18a and galnt18b, and with the other three isozymes each having a corresponding ortholog, galnt8, galnt9, and galnt17. The galnt8 was expressed in the cephalic mesoderm and hatching gland during early developmental stages, and differently expressed in the head, somatic muscles, and liver in the later stages. The other three orthologs also exhibited the characteristic expression patterns, although their expressions were generally strong in the nervous systems. In addition to the expression in the brain, galnt17 and galnt18a were expressed in the somitic muscles, and galnt18a and galnt18b in the notochord. These expression patterns may contribute to the functional analysis of the Y-subfamily, whose physiological roles still remain to be elucidated.

Fgf22 regulated by Fgf3/Fgf8 signaling is required for zebrafish midbrain development.

Fibroblast growth factor (Fgf) signaling plays important roles in various developmental processes including brain development. Here, we identified zebrafish fgf22 predominantly expressed in the posterior midbrain and anterior midbrain-hindbrain boundary (MHB) primordia during early embryonic brain development. To examine roles of Fgf22 in midbrain development, we analyzed fgf22 knockdown embryos. The fgf22 morphants were defective in proper formation of the MHB constriction and the midbrain. The knockdown of fgf22 caused decreased cell proliferation in the midbrain, expanded expression of roof plate and tegmental marker genes, and decreased expression of tectal marker genes, indicating that Fgf22 is required for cell proliferation, roof plate formation, and tectum specification in the midbrain. Fgf receptor 2b (Fgfr2b), a potential receptor for Fgf22, was also required, indicating that Fgf22 signaling is mediated through Fgfr2b. The floor plate and the MHB are crucial for the dorsoventral patterning of the midbrain through Hedgehog (Hh) and Fgf signaling, respectively. The fgf3/fgf8 double morphant phenotype was essentially similar to that of fgf22 morphants, whereas the phenotype caused by inhibition of Hh signaling was not. fgf3 and fgf8 were expressed earlier than fgf22 in the MHB primordium and Fgf3/Fgf8 signaling was required for fgf22 expression in the posterior midbrain. Furthermore, fgf22 partially rescued the fgf3/fgf8 double morphant phenotype. The present results indicate Fgf22 to be involved in midbrain development downstream of Fgf3 and Fgf8 in the MHB but not of Hh in the floor plate.

Neucrin, a novel secreted antagonist of canonical Wnt signaling, plays roles in developing neural tissues in zebrafish.

Wnt signaling plays crucial roles in neural development. We previously identified Neucrin, a neural-specific secreted antagonist of canonical Wnt/ß-catenin signaling, in humans and mice. Neucrin has one cysteine-rich domain, in which the positions of 10 cysteine residues are similar to those in the second cysteine-rich domain of Dickkopfs, secreted Wnt antagonists. Here, we have identified zebrafish neucrin to understand its roles in vivo. Zebrafish Neucrin also has one cysteine-rich domain, which is significantly similar to that of mouse Neucrin. Zebrafish neucrin was also predominantly expressed in developing neural tissues. To examine roles of neucrin in neural development, we analyzed neucrin knockdown embryos. Neural development in zebrafish embryos was impaired by the knockdown of neucrin. The knockdown of neucrin caused increased expression of the Wnt/ß-catenin target genes. In contrast, overexpression of neucrin reduced the expression of the Wnt/ß-catenin target genes. The knockdown of neucrin affected specification of dorsal region in the midbrain and hindbrain. The knockdown of neucrin also suppressed neuronal differentiation and caused increased cell proliferation and apoptosis in developing neural tissues. Neucrin is a unique secreted Wnt antagonist that is predominantly expressed in developing neural tissues and plays roles in neural development in zebrafish.