The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Tanya T. Whitfield - One of the best experts on this subject based on the ideXlab platform.
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Proposed gene network and timeline for the acquisition of anterior identity in the zebrafish Otic Vesicle.
2019Co-Authors: Ryan D. Hartwell, Samantha J. England, Nicholas A. M. Monk, Nicholas J. Van Hateren, Sarah Baxendale, Mar Marzo, Katharine E. Lewis, Tanya T. WhitfieldAbstract:(A) Proposed gene regulatory network. (B) Schematic timeline showing sequential onset of expression of anterior markers in the zebrafish Otic placode and Vesicle. Diagrams in A and B are based on the results of this study, together with previously published data [2–6, 9, 11, 12, 28]. Abbreviations: Fgfe, extrinsic Fgf protein; fgfi, intrinsic (Otic Vesicle) fgf gene expression; Hhe, extrinsic Hedgehog protein; hpf, hours post fertilisation; ss, somite stage.
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A model for the acquisition of anterior identity in the zebrafish Otic Vesicle.
2019Co-Authors: Ryan D. Hartwell, Samantha J. England, Nicholas A. M. Monk, Nicholas J. Van Hateren, Sarah Baxendale, Mar Marzo, Katharine E. Lewis, Tanya T. WhitfieldAbstract:Solutions of a differential equation-based model to describe gene expression dynamics of the proposed network. Endogenous mRNA expression levels (blue) are shown as a function of position along the Otic anteroposterior axis (x axis; % Otic Vesicle length from the anterior end) and time (y axis; hpf). Levels are shown in arbitrary units in the bars to the right of each panel. Exogenous fgf3 mRNA from the transgene after heat shock is not shown. Left-hand column: wild type; middle column: with transient heat-shock induction of fgf3 at 14 hpf; right-hand column: with inhibition of Hh signalling (cyclopamine treatment from 14–22.5 hpf). For full details, see S1 Model.
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Otic expression of fgf genes following mis-expression of fgf3 or inhibition of Hh signalling.
2019Co-Authors: Ryan D. Hartwell, Samantha J. England, Nicholas A. M. Monk, Nicholas J. Van Hateren, Sarah Baxendale, Mar Marzo, Katharine E. Lewis, Tanya T. WhitfieldAbstract:(A–F’) In situ hybridisation for Otic expression of fgf genes in Tg(hsp70:fgf3) embryos following a 30-minute heat shock (HS) at the 10-somite stage (14 hpf). Controls (left-hand panels of each pair of images) were sibling non-transgenic (Non-Tg) embryos subjected to the same heat shock. Numbers of embryos shown in the dorsal view panels indicate the number showing the phenotype from a mixed batch of transgenic and non-transgenic embryos in each pair of panels; 75% of the batch is expected to be transgenic. A–B’ show staining with a probe specific to the 3’ UTR of fgf3: note the ectopic patch of endogenous fgf3 expression at the posterior Otic pole (B,B’; arrowheads) and disruption to fgf3 expression ventral to the Otic Vesicle (B’; asterisks) after heat shock in transgenic embryos. Expression of fgf10a is strengthened in the Otic Vesicle of transgenic embryos after heat shock (E–F’). (G–Q’) Expression of mRNA for fgf genes in embryos treated with 100 μM cyclopamine (cyc) from the 10-somite stage (14 hpf) until 22.5 hpf. Controls in the left-hand panels of each pair of images were treated with vehicle (ethanol) only. Numbers of embryos with the phenotype shown for individual treatments are indicated in the dorsal view panels. There was little change to the Otic expression patterns of fgf3 or fgf8a at 22.5 hpf (8.5 hours post treatment) (G–J’), but note the loss of fgf3 expression ventral to the ear (H’; asterisk). Expression of fgf10a in the Otic Vesicle was strengthened after inhibition of Hh signalling in about 50% of treated embryos (L,L’). At 36 hpf (8.5 hpt + 13.5 h wash), ectopic expression of both fgf3 and fgf8a appeared in a new posteromedial domain in the ears of cyclopamine-treated embryos (M-P’; arrowheads). (Q,Q’) Expression of fgf8a in the posterior of the Otic Vesicle at 48 hpf (8.5 hpt + 25.5 h wash). Ectopic expression has strengthened (arrowhead) and medial epithelium is thinner than normal (brackets). Dorsal views of the left ear, with anterior to the top. Scale bar in A, 50 μm (applies to A–L); scale bar in A’, 50 μm (applies to A’–L’); scale bar in M, 50 μm (applies to M–P); scale bar in M’, 50 μm (applies to M’–P’); scale bar in Q, 20 μm (applies to Q,Q’).
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RA and FGF signalling are required in the zebrafish Otic Vesicle to pattern and maintain ventral Otic identities.
PLoS genetics, 2014Co-Authors: Esther C. Maier, Tanya T. WhitfieldAbstract:During development of the zebrafish inner ear, regional patterning in the ventral half of the Otic Vesicle establishes zones of gene expression that correspond to neurogenic, sensory and non-neural cell fates. FGF and Retinoic acid (RA) signalling from surrounding tissues are known to have an early role in Otic placode induction and Otic axial patterning, but how external signalling cues are translated into intrinsic patterning during Otic Vesicle (OV) stages is not yet understood. FGF and RA signalling pathway members are expressed in and around the OV, suggesting important roles in later patterning or maintenance events. We have analysed the temporal requirement of FGF and RA signalling for Otic development at stages after initial anteroposterior patterning has occurred. We show that high level FGF signalling acts to restrict sensory fates, whereas low levels favour sensory hair cell development; in addition, FGF is both required and sufficient to promote the expression of the non-neural marker otx1b in the OV. RA signalling has opposite roles: it promotes sensory fates, and restricts otx1b expression and the development of non-neural fates. This is surprisingly different from the earlier requirement for RA signalling in specification of non-neural fates via tbx1 expression, and highlights the shift in regulation that takes place between Otic placode and Vesicle stages in zebrafish. Both FGF and RA signalling are required for the development of the Otic neurogenic domain and the generation of Otic neuroblasts. In addition, our results indicate that FGF and RA signalling act in a feedback loop in the anterior OV, crucial for pattern refinement.
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The role of hair cells, cilia and ciliary motility in otolith formation in the zebrafish Otic Vesicle
Development (Cambridge England), 2012Co-Authors: Georgina A. Stooke-vaughan, Peng Huang, Katherine L. Hammond, Alexander F. Schier, Tanya T. WhitfieldAbstract:Otoliths are biomineralised structures required for the sensation of gravity, linear acceleration and sound in the zebrafish ear. Otolith precursor particles, initially distributed throughout the Otic Vesicle lumen, become tethered to the tips of hair cell kinocilia (tether cilia) at the Otic Vesicle poles, forming two otoliths. We have used high-speed video microscopy to investigate the role of cilia and ciliary motility in otolith formation. In wild-type ears, groups of motile cilia are present at the Otic Vesicle poles, surrounding the immotile tether cilia. A few motile cilia are also found on the medial wall, but most cilia (92-98%) in the Otic Vesicle are immotile. In mutants with defective cilia (iguana) or ciliary motility (lrrc50), otoliths are frequently ectopic, untethered or fused. Nevertheless, neither cilia nor ciliary motility are absolutely required for otolith tethering: a mutant that lacks cilia completely (MZovl) is still capable of tethering otoliths at the Otic Vesicle poles. In embryos with attenuated Notch signalling [mindbomb mutant or Su(H) morphant], supernumerary hair cells develop and otolith precursor particles bind to the tips of all kinocilia, or bind directly to the hair cells' apical surface if cilia are absent [MZovl injected with a Su(H)1+2 morpholino]. However, if the first hair cells are missing (atoh1b morphant), otolith formation is severely disrupted and delayed. Our data support a model in which hair cells produce an otolith precursor-binding factor, normally localised to tether cell kinocilia. We also show that embryonic movement plays a minor role in the formation of normal otoliths.
Bernice E Morrow - One of the best experts on this subject based on the ideXlab platform.
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tbx1 and jag1 act in concert to modulate the fate of neurosensory cells of the mouse Otic Vesicle
Biology Open, 2017Co-Authors: Stephania Macchiarulo, Bernice E MorrowAbstract:ABSTRACT The domain within the Otic Vesicle (OV) known as the neurosensory domain (NSD), contains cells that will give rise to the hair and support cells of the Otic sensory organs, as well as the neurons that form the cochleovestibular ganglion (CVG). The molecular dynamics that occur at the NSD boundary relative to adjacent OV cells is not well defined. The Tbx1 transcription factor gene expression pattern is complementary to the NSD, and inactivation results in expansion of the NSD and expression of the Notch ligand, Jag1 mapping, in part of the NSD. To shed light on the role of Jag1 in NSD development, as well as to test whether Tbx1 and Jag1 might genetically interact to regulate this process, we inactivated Jag1 within the Tbx1 expression domain using a knock-in Tbx1 Cre allele. We observed an enlarged neurogenic domain marked by a synergistic increase in expression of NeuroD and other proneural transcription factor genes in double Tbx1 and Jag1 conditional loss-of-function embryos. We noted that neuroblasts preferentially expanded across the medial-lateral axis and that an increase in cell proliferation could not account for this expansion, suggesting that there was a change in cell fate. We also found that inactivation of Jag1 with Tbx1 Cre resulted in failed development of the cristae and semicircular canals, as well as notably fewer hair cells in the ventral epithelium of the inner ear rudiment when inactivated on a Tbx1 null background, compared to Tbx1 Cre/− mutant embryos. We propose that loss of expression of Tbx1 and Jag1 within the Tbx1 expression domain tips the balance of cell fates in the NSD, resulting in an overproduction of neuroblasts at the expense of non-neural cells within the OV.
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Dual embryonic origin of the mammalian Otic Vesicle forming the inner ear
Development (Cambridge England), 2011Co-Authors: Laina Freyer, Vimla Aggarwal, Bernice E MorrowAbstract:The inner ear and cochleovestibular ganglion (CVG) derive from a specialized region of head ectoderm termed the Otic placode. During embryogenesis, the Otic placode invaginates into the head to form the Otic Vesicle (OV), the primordium of the inner ear and CVG. Non-autonomous cell signaling from the hindbrain to the OV is required for inner ear morphogenesis and neurogenesis. In this study, we show that neuroepithelial cells (NECs), including neural crest cells (NCCs), can contribute directly to the OV from the neural tube. Using Wnt1-Cre, Pax3(Cre/+) and Hoxb1(Cre/+) mice to label and fate map cranial NEC lineages, we have demonstrated that cells from the neural tube incorporate into the Otic epithelium after Otic placode induction has occurred. Pax3(Cre/+) labeled a more extensive population of NEC derivatives in the OV than did Wnt1-Cre. NEC derivatives constitute a significant population of the OV and, moreover, are regionalized specifically to proneurosensory domains. Descendents of Pax3(Cre/+) and Wnt1-Cre labeled cells are localized within sensory epithelia of the saccule, utricle and cochlea throughout development and into adulthood, where they differentiate into hair cells and supporting cells. Some NEC derivatives give rise to neuroblasts in the OV and CVG, in addition to their known contribution to glial cells. This study defines a dual cellular origin of the inner ear from sensory placode ectoderm and NECs, and changes the current paradigm of inner ear neurosensory development.
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canonical wnt signaling modulates tbx1 eya1 and six1 expression restricting neurogenesis in the Otic Vesicle
Developmental Dynamics, 2010Co-Authors: Laina Freyer, Bernice E MorrowAbstract:To understand the mechanism by which canonical Wnt signaling sets boundaries for pattern formation in the Otic Vesicle (OV), we examined Tbx1 and Eya1-Six1 downstream of activated β-catenin. Tbx1, the gene for velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), is essential for inner ear development where it promotes Bmp4 and Otx1 expression and restricts neurogenesis. Using floxed β-catenin gain-of-function (GOF) and loss-of-function (LOF) alleles, we found Tbx1 expression was down-regulated and maintained/enhanced in the two mouse mutants, respectively. Bmp4 was ectopically expressed and Otx1 was lost in β-catenin GOF mutants. Normally, inactivation of Tbx1 causes expanded neurogenesis, but expression of NeuroD was down-regulated in β-catenin GOF mutants. To explain this paradox, Eya1 and Six1, genes for branchio-oto-renal (BOR) syndrome were down-regulated in the OV of β-catenin GOF mutants independently of Tbx1. Overall, this work helps explain the mechanism by which Wnt signaling modulates transcription factors required for neurogenesis and patterning of the OV. Developmental Dynamics 239:1708–1722, 2010. © 2010 Wiley-Liss, Inc.
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Canonical Wnt signaling modulates Tbx1, Eya1, and Six1 expression, restricting neurogenesis in the Otic Vesicle.
Developmental dynamics : an official publication of the American Association of Anatomists, 2010Co-Authors: Laina Freyer, Bernice E MorrowAbstract:To understand the mechanism by which canonical Wnt signaling sets boundaries for pattern formation in the Otic Vesicle (OV), we examined Tbx1 and Eya1-Six1 downstream of activated beta-catenin. Tbx1, the gene for velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), is essential for inner ear development where it promotes Bmp4 and Otx1 expression and restricts neurogenesis. Using floxed beta-catenin gain-of-function (GOF) and loss-of-function (LOF) alleles, we found Tbx1 expression was down-regulated and maintained/enhanced in the two mouse mutants, respectively. Bmp4 was ectopically expressed and Otx1 was lost in beta-catenin GOF mutants. Normally, inactivation of Tbx1 causes expanded neurogenesis, but expression of NeuroD was down-regulated in beta-catenin GOF mutants. To explain this paradox, Eya1 and Six1, genes for branchio-oto-renal (BOR) syndrome were down-regulated in the OV of beta-catenin GOF mutants independently of Tbx1. Overall, this work helps explain the mechanism by which Wnt signaling modulates transcription factors required for neurogenesis and patterning of the OV.
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Tbx1 and Brn4 regulate retinoic acid metabolic genes during cochlear morphogenesis
BMC developmental biology, 2009Co-Authors: Evan M. Braunstein, Vimla Aggarwal, Dennis C. Monks, Jelena S. Arnold, Bernice E MorrowAbstract:In vertebrates, the inner ear is comprised of the cochlea and vestibular system, which develop from the Otic Vesicle. This process is regulated via inductive interactions from surrounding tissues. Tbx1, the gene responsible for velo-cardio-facial syndrome/DiGeorge syndrome in humans, is required for ear development in mice. Tbx1 is expressed in the Otic epithelium and adjacent periOtic mesenchyme (POM), and both of these domains are required for inner ear formation. To study the function of Tbx1 in the POM, we have conditionally inactivated Tbx1 in the mesoderm while keeping expression in the Otic Vesicle intact. Conditional mutants (TCre-KO) displayed malformed inner ears, including a hypoplastic Otic Vesicle and a severely shortened cochlear duct, indicating that Tbx1 expression in the POM is necessary for proper inner ear formation. Expression of the mesenchyme marker Brn4 was also lost in the TCre-KO. Brn4-;Tbx1+/-embryos displayed defects in growth of the distal cochlea. To identify a potential signal from the POM to the Otic epithelium, expression of retinoic acid (RA) catabolizing genes was examined in both mutants. Cyp26a1 expression was altered in the TCre-KO, while Cyp26c1 showed reduced expression in both TCre-KO and Brn4-;Tbx1+/- embryos. These results indicate that Tbx1 expression in the POM regulates cochlear outgrowth potentially via control of local retinoic acid activity.
Fernando Giraldez - One of the best experts on this subject based on the ideXlab platform.
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Insulin-like growth factor 1 is required for survival of transit-amplifying neuroblasts and differentiation of Otic neurons.
Developmental biology, 2003Co-Authors: Guadalupe Camarero, Fernando Giraldez, Yolanda León, Itziar Gorospe, F De Pablo, Berta Alsina, Isabel Varela-nietoAbstract:Neurons that connect mechanosensory hair cell receptors to the central nervous system derive from the Otic Vesicle from where Otic neuroblasts delaminate and form the cochleovestibular ganglion (CVG). Local signals interact to promote this process, which is autonomous and intrinsic to the Otic Vesicle. We have studied the expression and activity of insulin-like growth factor-1 (IGF-1) during the formation of the chick CVG, focusing attention on its role in neurogenesis. IGF-1 and its receptor (IGFR) were detected at the mRNA and protein levels in the Otic epithelium and the CVG. The function of IGF-1 was explored in explants of Otic Vesicle by assessing the formation of the CVG in the presence of anti-IGF-1 antibodies or the receptor competitive antagonist JB1. Interference with IGF-1 activity inhibited CVG formation in growth factor-free media, revealing that endogenous IGF-1 activity is essential for ganglion generation. Analysis of cell proliferation cell death, and expression of the early neuronal antigens Tuj-1, Islet-1/2, and G4 indicated that IGF-1 was required for survival, proliferation, and differentiation of an actively expanding population of Otic neuroblasts. IGF-1 blockade, however, did not affect NeuroD within the Otic epithelium. Experiments carried out on isolated CVG showed that exogenous IGF-1 induced cell proliferation, neurite outgrowth, and G4 expression. These effects of IGF-1 were blocked by JB1. These findings suggest that IGF-1 is essential for neurogenesis by allowing the expansion of a transit-amplifying neuroblast population and its differentiation into postmitOtic neurons. IGF-1 is one of the signals underlying autonomous development of the Otic Vesicle.
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Regionalized Organizing Activity of the Neural Tube Revealed by the Regulation of lmx1 in the Otic Vesicle
Developmental biology, 1998Co-Authors: Fernando GiraldezAbstract:LIM homeodomain genes have been involved in patterning in a variety of organisms. I have analyzed the expression of lmx1 during early ear development and explored its regulation by the neuroectoderm. Experiments were carried out on chick embryos. During early somitic stages (4-6 somites), lmx1 was expressed in the neural tube and in a stripe of the dorsal ectoderm. The ectodermal expression domain was then restricted to the Otic placode (7-10 somites). At Otic cup stages, lmx1 was downregulated in ventral and medial aspects of the Otic epithelium facing the neural tube. This resulted in a dorsal and lateral restriction of lmx1 that persisted until the Otic Vesicle stage. The dependence of lmx1 on interactions with the neuroectoderm was explored by carrying out ablations of the neural tube in organotypic explants containing the Otic presumptive ectoderm. Both the formation of the Otic Vesicle and expression of lmx1 were dependent on the presence of the neural ectoderm during stages preceding placode formation (4-6 somites). Thereafter, the formation of the Otic Vesicle was progressively autonomous, and by the stage of 10 somites the Otic ectoderm developed into Otic Vesicles and expressed lmx1 in foreign environments. Dorsal and ventral neuroectoderms displayed differential effects on lmx1 expression. Ablation of the dorsal neural tube resulted in a reduced expression of lmx1, which was more dramatic during early placode and preplacode stages (5-7 somites). Removal of the ventral aspect of the neural tube (including the notochord) had opposite effects, expression of lmx1 increased, and its domain expanded. The formation of the Otic Vesicle, however, was supported by either the dorsal or ventral neuroectoderm. The experiments suggest that lmx1 is involved in early patterning of the Otic Vesicle, and they provide evidence for the regional segregation of organizing activities within the neural tube.
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6 Organoculture of Otic Vesicle and Ganglion
Current topics in developmental biology, 1998Co-Authors: Juan José Garrido, Thomas Schimmang, J Represa, Fernando GiraldezAbstract:Publisher Summary Organ culture techniques applied to the Otic Vesicle and cochleovestibular ganglion (CVG) have allowed progress in the study of the role of growth factors in the regulation of cell proliferation in sensory organs. The CVG contains the primary afferent neurons that connect the sensory epithelia of the inner ear with the central nervous system. It originates from the Otic Vesicle and neural crest, and goes through a period of intense cell proliferation until neuroblasts become postmitOtic and start to differentiate. The earliest morphologic evidence for the primordium of the ear is the Otic placode, a thickened area of ectoderm close to the hindbrain. It can be recognized in apposition to the neural tube as early as from the 3-6-somite embryo, depending on the animal species. The Otic placode then invaginates to form the Otic Vesicle. The latter consists of a cavity lined by a pseudostratified epithelium of high proliferative activity. The Otic Vesicle is developmentally autonomous and it contains all information concerning the organization of the membranous labyrinth and the different cellular phenotypes.
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Developmental regulation of Fos-protein during proliferative growth of the Otic Vesicle and its relation to differentiation induced by retinoic acid.
Developmental biology, 1995Co-Authors: Yolanda León, J.a. Sanchez, Cristina Miner, L. Ariza-mcnaughton, J.j. Represa, Fernando GiraldezAbstract:This work studies Fos protein expression in the Otic Vesicle and the developing cochleovestibular ganglion (CVG), focusing on the possible role of Fos in the regulation of cell proliferation and differentiation during Otic development. Fos was detected as a product of 56-62 kDa in Otic Vesicles and CVG lysates. Expression was transient and stage-dependent. Maximal levels occurred at stage 20 in the Otic Vesicle and at Day 4 in the CVG. Another wave of Fos expression occurred after Day 7 of development, out of the early proliferative period. Fos immunoreactivity was localized in cell nuclei of Otic epithelium and CVG. Fos was readily induced by mitogens like serum and bombesin and this induction was inhibited by 25 nM retinoic acid, an inhibitor of cell proliferation in the Otic Vesicle.c-fos antisense oligonucleotides inhibited growth in the Otic Vesicle in parallel with a reduction in Fos expression. High levels of Fos protein were not sufficient, however, to sustain growth of isolated Otic Vesicles in the absence of mitogens. Incubation with retinoic acid (24 hr) induced differentiation of sensory hair-cells in parallel with inhibition of cell proliferation. Contrary to retinoic acid, Fos inhibition by antisense did not induce differentiation. The results suggest that Fos is part of the signaling mechanisms regulating normal development of the inner ear. Regulation of Fos may be required for controlling of the transition between cell proliferation and differentiation.
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The int-2 proto-oncogene is responsible for induction of the inner ear
Nature, 1991Co-Authors: Juan Represa, Yolanda León, Cristina Miner, Fernando GiraldezAbstract:THE int-2 proto-oncogene encodes several products related to the fibroblast growth factor (FGF) family1,2. FGFs have been associated with mesoderm induction in the amphibian embryo2,3 and int-2 has a distinct pattern of expression throughout development in vertebrates4,5. But evidence for a function of int-2 in embryo-genesis has been lacking. In the mouse embryo, int-2 transcripts have been detected in the rhombencephalon at a developmental stage where classical experiments showed that the induction of the inner ear occurs6,7. This raises the possibility that int-2 may constitute a signal for the induction of the Otic Vesicle, the primor-dium of the inner ear. We provide direct evidence for this view by showing that (1) the formation of the Otic Vesicle is inhibited by antisense oligonucleotides targeted to the secreted form of int-2, and by antibodies against int-2 oncoproteins, and (2) basic FGF (bFGF) can mimic the inductive signal in the absence of the rhombencephalon.
Bruce B. Riley - One of the best experts on this subject based on the ideXlab platform.
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The Warburg Effect and lactate signaling augment Fgf-MAPK to promote sensory-neural development in the Otic Vesicle.
eLife, 2020Co-Authors: Husniye Kantarci, Yunzi Gou, Bruce B. RileyAbstract:Recent studies indicate that many developing tissues modify glycolysis to favor lactate synthesis (Agathocleous et al., 2012; Bulusu et al., 2017; Gu et al., 2016; Oginuma et al., 2017; Sá et al., 2017; Wang et al., 2014; Zheng et al., 2016), but how this promotes development is unclear. Using forward and reverse genetics in zebrafish, we show that disrupting the glycolytic gene phosphoglycerate kinase-1 (pgk1) impairs Fgf-dependent development of hair cells and neurons in the Otic Vesicle and other neurons in the CNS/PNS. Fgf-MAPK signaling underperforms in pgk1- / - mutants even when Fgf is transiently overexpressed. Wild-type embryos treated with drugs that block synthesis or secretion of lactate mimic the pgk1- / - phenotype, whereas pgk1- / - mutants are rescued by treatment with exogenous lactate. Lactate treatment of wild-type embryos elevates expression of Etv5b/Erm even when Fgf signaling is blocked. However, lactate's ability to stimulate neurogenesis is reversed by blocking MAPK. Thus, lactate raises basal levels of MAPK and Etv5b (a critical effector of the Fgf pathway), rendering cells more responsive to dynamic changes in Fgf signaling required by many developing tissues.
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The Warburg effect and lactate signaling augment Fgf signaling to promote sensory-neural development in the Otic Vesicle
2018Co-Authors: Bruce B. Riley, Husniye Kantarci, Yunzi GouAbstract:Recent studies indicate that many developing tissues modify glycolysis to favor lactate synthesis, but how this promotes development is unclear. Using forward and reverse genetics in zebrafish, we show that disrupting the glycolytic gene phosphoglycerate kinase-1 (pgk1) impairs Fgf-dependent development of hair cells and neurons in the Otic Vesicle and other neurons in the CNS/PNS. Focusing on the Otic Vesicle, we found that Fgf signaling underperforms in pgk1-/- mutants even when Fgf is transiently overexpressed. Wild-type embryos treated with drugs that block synthesis or secretion of lactate mimic the pgk1-/- phenotype, whereas pgk1-/- mutants are rescued by treatment with exogenous lactate. Lactate treatment of wild-type embryos elevates expression of Etv5b/Erm even when Fgf signaling is blocked. Thus, by raising steady-state levels of Etv5b (a critical effector of the Fgf pathway), lactate renders cells more responsive to dynamic changes in Fgf signaling required by many developing tissues.
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Spemann organizer gene Goosecoid promotes delamination of neuroblasts from the Otic Vesicle
Proceedings of the National Academy of Sciences, 2016Co-Authors: Husniye Kantarci, Andrea Gerberding, Bruce B. RileyAbstract:Neurons of the Statoacoustic Ganglion (SAG), which innervate the inner ear, originate as neuroblasts in the floor of the Otic Vesicle and subsequently delaminate and migrate toward the hindbrain before completing differentiation. In all vertebrates, locally expressed Fgf initiates SAG development by inducing expression of Neurogenin1 (Ngn1) in the floor of the Otic Vesicle. However, not all Ngn1-positive cells undergo delamination, nor has the mechanism controlling SAG delamination been elucidated. Here we report that Goosecoid (Gsc), best known for regulating cellular dynamics in the Spemann organizer, regulates delamination of neuroblasts in the Otic Vesicle. In zebrafish, Fgf coregulates expression of Gsc and Ngn1 in partially overlapping domains, with delamination occurring primarily in the zone of overlap. Loss of Gsc severely inhibits delamination, whereas overexpression of Gsc greatly increases delamination. Comisexpression of Ngn1 and Gsc induces ectopic delamination of some cells from the medial wall of the Otic Vesicle but with a low incidence, suggesting the action of a local inhibitor. The medial marker Pax2a is required to restrict the domain of gsc expression, and misexpression of Pax2a is sufficient to block delamination and fully suppress the effects of Gsc The opposing activities of Gsc and Pax2a correlate with repression or up-regulation, respectively, of E-cadherin (cdh1). These data resolve a genetic mechanism controlling delamination of Otic neuroblasts. The data also elucidate a developmental role for Gsc consistent with a general function in promoting epithelial-to-mesenchymal transition (EMT).
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RESEARCH ARTICLE Tfap2a Promotes Specification and Maturation of Neurons in the Inner Ear through Modulation of Bmp, Fgf and Notch Signaling
2016Co-Authors: Husniye Kantarci, Renee K. Edlund, Andrew K. Groves, Bruce B. RileyAbstract:Neurons of the statoacoustic ganglion (SAG) transmit auditory and vestibular information from the inner ear to the hindbrain. SAG neuroblasts originate in the floor of the Otic Vesicle. New neuroblasts soon delaminate and migrate towards the hindbrain while continuing to pro-liferate, a phase known as transit amplification. SAG cells eventually come to rest between the ear and hindbrain before terminally differentiating. Regulation of these events is only par-tially understood. Fgf initiates neuroblast specification within the ear. Subsequently, Fgf se-creted by mature SAG neurons exceeds a maximum threshold, serving to terminate specification and delay maturation of transit-amplifying cells. Notch signaling also limits SAG development, but how it is coordinated with Fgf is unknown. Here we show that transcription factor Tfap2a coordinates multiple signaling pathways to promote neurogenesis in the zebra-fish inner ear. In both zebrafish and chick, Tfap2a is expressed in a ventrolateral domain of the Otic Vesicle that includes neurogenic precursors. Functional studies were conducted in zebrafish. Loss of Tfap2a elevated Fgf and Notch signaling, thereby inhibiting SAG specifica-tion and slowing maturation of transit-amplifying cells. Conversely, overexpression of Tfap2
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Sox2 and Fgf interact with Atoh1 to promote sensory competence throughout the zebrafish inner ear
Developmental biology, 2011Co-Authors: Elly M. Sweet, Shruti Vemaraju, Bruce B. RileyAbstract:Atoh1 is required for differentiation of sensory hair cells in the vertebrate inner ear. Moreover, misexpression of Atoh1 is sufficient to establish ectopic sensory epithelia, making Atoh1 a good candidate for gene therapy to restore hearing. However, competence to form sensory epithelia appears to be limited to discrete regions of the inner ear. To better understand the developmental factors influencing sensory-competence, we examined the effects of misexpressing atoh1a in zebrafish embryos under various developmental conditions. Activation of a heat shock-inducible transgene, hs:atoh1a, resulted in ectopic expression of early markers of sensory development within 2h, and mature hair cells marked by brn3c:GFP began to accumulate 9h after heat shock. The ability of atoh1a to induce ectopic sensory epithelia was maximal when activated during placodal or early Otic Vesicle stages but declined rapidly thereafter. At no stage was atoh1a sufficient to induce sensory development in dorsal or lateral non-sensory regions of the Otic Vesicle. However, co-misexpression of atoh1a with fgf3, fgf8 or sox2, genes normally acting in the same gene network with atoh1a, stimulated sensory development in all regions of the Otic Vesicle. Thus, expression of fgf3, fgf8 or sox2 strongly enhances competence to respond to Atoh1.
Laina Freyer - One of the best experts on this subject based on the ideXlab platform.
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Dual embryonic origin of the mammalian Otic Vesicle forming the inner ear
Development (Cambridge England), 2011Co-Authors: Laina Freyer, Vimla Aggarwal, Bernice E MorrowAbstract:The inner ear and cochleovestibular ganglion (CVG) derive from a specialized region of head ectoderm termed the Otic placode. During embryogenesis, the Otic placode invaginates into the head to form the Otic Vesicle (OV), the primordium of the inner ear and CVG. Non-autonomous cell signaling from the hindbrain to the OV is required for inner ear morphogenesis and neurogenesis. In this study, we show that neuroepithelial cells (NECs), including neural crest cells (NCCs), can contribute directly to the OV from the neural tube. Using Wnt1-Cre, Pax3(Cre/+) and Hoxb1(Cre/+) mice to label and fate map cranial NEC lineages, we have demonstrated that cells from the neural tube incorporate into the Otic epithelium after Otic placode induction has occurred. Pax3(Cre/+) labeled a more extensive population of NEC derivatives in the OV than did Wnt1-Cre. NEC derivatives constitute a significant population of the OV and, moreover, are regionalized specifically to proneurosensory domains. Descendents of Pax3(Cre/+) and Wnt1-Cre labeled cells are localized within sensory epithelia of the saccule, utricle and cochlea throughout development and into adulthood, where they differentiate into hair cells and supporting cells. Some NEC derivatives give rise to neuroblasts in the OV and CVG, in addition to their known contribution to glial cells. This study defines a dual cellular origin of the inner ear from sensory placode ectoderm and NECs, and changes the current paradigm of inner ear neurosensory development.
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canonical wnt signaling modulates tbx1 eya1 and six1 expression restricting neurogenesis in the Otic Vesicle
Developmental Dynamics, 2010Co-Authors: Laina Freyer, Bernice E MorrowAbstract:To understand the mechanism by which canonical Wnt signaling sets boundaries for pattern formation in the Otic Vesicle (OV), we examined Tbx1 and Eya1-Six1 downstream of activated β-catenin. Tbx1, the gene for velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), is essential for inner ear development where it promotes Bmp4 and Otx1 expression and restricts neurogenesis. Using floxed β-catenin gain-of-function (GOF) and loss-of-function (LOF) alleles, we found Tbx1 expression was down-regulated and maintained/enhanced in the two mouse mutants, respectively. Bmp4 was ectopically expressed and Otx1 was lost in β-catenin GOF mutants. Normally, inactivation of Tbx1 causes expanded neurogenesis, but expression of NeuroD was down-regulated in β-catenin GOF mutants. To explain this paradox, Eya1 and Six1, genes for branchio-oto-renal (BOR) syndrome were down-regulated in the OV of β-catenin GOF mutants independently of Tbx1. Overall, this work helps explain the mechanism by which Wnt signaling modulates transcription factors required for neurogenesis and patterning of the OV. Developmental Dynamics 239:1708–1722, 2010. © 2010 Wiley-Liss, Inc.
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Canonical Wnt signaling modulates Tbx1, Eya1, and Six1 expression, restricting neurogenesis in the Otic Vesicle.
Developmental dynamics : an official publication of the American Association of Anatomists, 2010Co-Authors: Laina Freyer, Bernice E MorrowAbstract:To understand the mechanism by which canonical Wnt signaling sets boundaries for pattern formation in the Otic Vesicle (OV), we examined Tbx1 and Eya1-Six1 downstream of activated beta-catenin. Tbx1, the gene for velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), is essential for inner ear development where it promotes Bmp4 and Otx1 expression and restricts neurogenesis. Using floxed beta-catenin gain-of-function (GOF) and loss-of-function (LOF) alleles, we found Tbx1 expression was down-regulated and maintained/enhanced in the two mouse mutants, respectively. Bmp4 was ectopically expressed and Otx1 was lost in beta-catenin GOF mutants. Normally, inactivation of Tbx1 causes expanded neurogenesis, but expression of NeuroD was down-regulated in beta-catenin GOF mutants. To explain this paradox, Eya1 and Six1, genes for branchio-oto-renal (BOR) syndrome were down-regulated in the OV of beta-catenin GOF mutants independently of Tbx1. Overall, this work helps explain the mechanism by which Wnt signaling modulates transcription factors required for neurogenesis and patterning of the OV.
