Fgf signalling is required for gill slit formation in the skate, Leucoraja erinacea

The gill slits of fishes develop from an iterative series of pharyngeal endodermal pouches that contact and fuse with surface ectoderm on either side of the embryonic head. We find in the skate (Leucoraja erinacea) that all gill slits form via a stereotypical sequence of epithelial interactions: 1) endodermal pouches approach overlying surface ectoderm, with 2) focal degradation of ectodermal basement membranes preceding endoderm-ectoderm contact; 3) endodermal pouches contact and intercalate with overlying surface ectoderm, and finally 4) perforation of a gill slit occurs by epithelial remodelling, without programmed cell death, at the site of endoderm-ectoderm intercalation. Skate embryos express Fgf8 and Fgf3 within developing pharyngeal epithelia during gill slit formation. When we inhibit Fgf signalling by treating skate embryos with the Fgf receptor inhibitor SU5402 we find that endodermal pouch formation, basement membrane degradation and endodermal-ectodermal intercalation are unaffected, but that epithelial remodelling and gill slit perforation fail to occur. These findings point to a role for Fgf signalling in epithelial remodelling during gill slit formation in the skate and, more broadly, to an ancestral role for Fgf signalling during pharyngeal pouch epithelial morphogenesis in vertebrate embryos.

High-throughput transcriptome sequencing reveals the critical role of long non-coding RNA Gm14376 in the occurrence of neuropathic pain

Long noncoding RNAs (lncRNAs) have been suggested as important regulators in neuropathic pain. Our study aims to explore the possible molecular mechanism underlying the role of long non-coding RNA (lncRNA) Gm14376 in neuropathic pain in mice by high-throughput transcriptome sequencing. A mouse model of spared nerve injury (SNI) was constructed for mechanical, thermal and spontaneous pain testing. Transcriptomic changes in lncRNAs and mRNAs in the dorsal root ganglion (DRG) of SNI mice were analyzed using RNA-sequencing techniques in conjunction with public data analysis. AAV5 viral vector was constructed to assess the effect of Gm14376 on SNI-induced pain hypersensitivity and inflammatory response. Cis-target genes of Gm14376 were obtained and the functions of Gm14376 were analyzed by GO and KEGG pathway enrichment analyses. Results from bioinformatic analysis identified a conserved Gm14376, which was up-regulated in the DRG of SNI mice, specifically in response to nerve injury. Overexpression of Gm14376 in DRG induced neuropathic pain-like symptoms in mice. Furthermore, the functions of Gm14376 were related to the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and fibroblast growth factor 3 (Fgf3) was identified as the cis-target gene of Gm14376. Gm14376 could directly up-regulate Fgf3 expression to activate the PI3K/Akt pathway, which alleviated pain hypersensitivity to mechanical and thermal stimuli and reduced the release of inflammatory factors in SNI mice. From our data, we conclude that SNI-induced up-regulation of Gm14376 expression in DRG activates the PI3K/Akt pathway through up-regulation of Fgf3 expression, thereby promoting the development of neuropathic pain in mice.

Mesenchymal Sufu Regulates Development of Mandibular Molars via Shh Signaling

Sonic hedgehog (Shh) in dental epithelium regulates tooth morphogenesis by epithelial-mesenchymal signaling transduction. However, the action of Shh signaling regulation in this process is not well understood. Here we find that mesenchymal Suppressor of Fused (Sufu), a major negative regulator of Shh signaling, plays an important role in modulating the tooth germ morphogenesis during the bud-to-cap stage transition. Deletion of Sufu in dental mesenchyme by Dermo1-Cre mice leads to delayed development of mandibular molar into cap stage with defect of primary enamel knot (EK) formation. We show the disruption of cell proliferation and programmed cell death in dental epithelium and mesenchyme in Sufu mutants. Epithelial-specific adhesion molecule E-cadherin is evidently reduced in the bilateral basal cells of tooth germ at E14.5. The cells in the presumptive EK, predominantly expressing P-cadherin, appear stratified but fail to condense. Moreover, the transcripts of primary EK marker genes, including Shh, Fgf4, and p21, are significantly decreased compared to controls. In contrast, we find that deficiency of Sufu results in elevation of Shh signaling in mesenchyme, indicated by the significant upregulation of Gli1 and Ptch1. Meanwhile, the expression of Bmp4 and Fgf3, the critical factors of mesenchymal-epithelial induction, is significantly inhibited in dental mesenchyme. Furthermore, the expression of Runx2 experiences a transient decrease at the bud stage. Taken together, these data suggest that mesenchymal Sufu is necessary for tuning the Shh signaling, which may act as an upstream modulator of Bmp4 and Fgf3 to coordinate the interplay between the dental mesenchyme and epithelium of tooth germ.

Different Fgfs have distinct roles in regulating neurogenesis after spinal cord injury in zebrafish

Background

Despite conserved developmental processes and organization of the vertebrate central nervous system, only some vertebrates including zebrafish can efficiently regenerate neural damage including after spinal cord injury. The mammalian spinal cord shows very limited regeneration and neurogenesis, resulting in permanent life-long functional impairment. Therefore, there is an urgent need to identify the cellular and molecular mechanisms that can drive efficient vertebrate neurogenesis following injury. A key pathway implicated in zebrafish neurogenesis is fibroblast growth factor signaling.

Methods

In the present study we investigated the roles of distinct fibroblast growth factor members and their receptors in facilitating different aspects of neural development and regeneration at different timepoints following spinal cord injury. After spinal cord injury in adults and during larval development, loss and/or gain of Fgf signaling was combined with immunohistochemistry, in situ hybridization and transgenes marking motor neuron populations in in vivo zebrafish and in vitro mammalian PC12 cell culture models.

Results

Fgf3 drives neurogenesis of Islet1 expressing motor neuron subtypes and mediate axonogenesis in cMet expressing motor neuron subtypes. We also demonstrate that the role of Fgf members are not necessarily simple recapitulating development. During development Fgf2, Fgf3 and Fgf8 mediate neurogenesis of Islet1 expressing neurons and neuronal sprouting of both, Islet1 and cMet expressing motor neurons. Strikingly in mammalian PC12 cells, all three Fgfs increased cell proliferation, however, only Fgf2 and to some extent Fgf8, but not Fgf3 facilitated neurite outgrowth.

Conclusions

This study demonstrates differential Fgf member roles during neural development and adult regeneration, including in driving neural proliferation and neurite outgrowth of distinct spinal cord neuron populations, suggesting that factors including Fgf type, age of the organism, timing of expression, requirements for different neuronal populations could be tailored to best drive all of the required regenerative processes.

Control of Wnt5b secretion by Wntless modulates chondrogenic cell proliferation through fine-tuning fgf3 expression

Wnts and Fgfs regulate various tissues development in vertebrates. However, how regional Wnt or Fgf activities are established and how they interact in any given developmental event is elusive. Here, we investigated the Wnt-mediated craniofacial cartilage development in zebrafish and found that fgf3 expression in the pharyngeal pouches is differentially reduced along the anteroposterior axis in wnt5b mutants and wntless (wls) morphants, but its expression is normal in wnt9a and wnt11 morphants. Introducing fgf3 mRNAs rescued the cartilage defects in Wnt5b- and Wls-deficient larvae. In wls morphants, endogenous Wls expression is not detectable but maternally deposited Wls is present in eggs, which might account for the lack of axis defects in wls morphants. Secretion of endogenous Wnt5b but not Wnt11 was affected in the pharyngeal tissue of Wls morphants, indicating that Wls is not involved in every Wnt secretion event. Furthermore, cell proliferation but not apoptosis in the developing jaw was affected in Wnt5b- and Wls-deficient embryos. Therefore, Wnt5b requires Wls for its secretion and regulates the proliferation of chondrogenic cells through fine-tuning the expression of fgf3 during jaw cartilage development.

Deletion of Osr2 Partially Rescues Tooth Development in Runx2 Mutant Mice

Tooth organogenesis depends on genetically programmed sequential and reciprocal inductive interactions between the dental epithelium and neural crest-derived mesenchyme. Previous studies showed that the Msx1 and Runx2 transcription factors are required for activation of odontogenic signals, including Bmp4 and Fgf3, in the early tooth mesenchyme to drive tooth morphogenesis through the bud-to-cap transition and that Runx2 acts downstream of Msx1 to activate Fgf3 expression. Recent studies identified Osr2 as a repressor of tooth development and showed that inactivation of Osr2 rescued molar tooth morphogenesis in the Msx1(-/-) mutant mice as well as in mice with neural crest-specific inactivation of Bmp4. Here we show that Runx2 expression is expanded in the tooth bud mesenchyme in Osr2(-/-) mutant mouse embryos and is partially restored in the tooth mesenchyme in Msx1(-/-)Osr2(-/-) mutants in comparison with Msx1(-/-) and wild-type embryos. Whereas mandibular molar development arrested at the bud stage and maxillary molar development arrested at the bud-to-cap transition in Runx2(-/-) mutant mice, both mandibular and maxillary molar tooth germs progressed to the early bell stage, with rescued expression of Msx1 and Bmp4 in the dental papilla as well as expression of Bmp4, p21, and Shh in the primary enamel knot in the Osr2(-/-)Runx2(-/-) compound mutants. In contrast to the Msx1(-/-)Osr2(-/-) compound mutants, which exhibit nearly normal first molar morphogenesis, the Osr2(-/-)Runx2(-/-) compound mutant embryos failed to activate the expression of Fgf3 and Fgf10 in the dental papilla and exhibited significant deficit in cell proliferation in both the dental epithelium and mesenchyme in comparison with the control embryos. These data indicate that Runx2 synergizes with Msx1 to drive tooth morphogenesis through the bud-to-cap transition and that Runx2 controls continued tooth growth and morphogenesis beyond the cap stage through activation of Fgf3 and Fgf10 expression in the dental papilla.

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.