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At least 991 records · Page 55Linked to original sources
PubMed2006

Wnt9a signaling is required for joint integrity and regulation of Ihh during chondrogenesis.

Joints, which separate skeleton elements, serve as important signaling centers that regulate the growth of adjacent cartilage elements by controlling proliferation and maturation of chondrocytes. Accurate chondrocyte maturation is crucial for endochondral ossification and for the ultimate size of skeletal elements, as premature or delayed maturation results predominantly in shortened elements. Wnt9a has previously been implicated as being a player in joint induction, based on gain-of function experiments in chicken and mouse. We show that loss of Wnt9a does not affect joint induction, but results to synovial chondroid metaplasia in some joints. This phenotype can be enhanced by removal of an additional Wnt gene, Wnt4, suggesting that Wnts are playing a crucial role in directing bi-potential chondro-synovioprogenitors to become synovial connective tissue, by actively suppressing their chondrogenic potential. Furthermore, we show that Wnt9a is a temporal and spatial regulator of Indian hedgehog (Ihh), a central player of skeletogenesis. Loss of Wnt9a activity results in transient downregulation of Ihh and reduced Ihh-signaling activity at E12.5-E13.5. The canonical Wnt/beta-catenin pathway probably mediates regulation of Ihh expression in prehypertrophic chondrocytes by Wnt9a, because embryos double-heterozygous for Wnt9a and beta-catenin show reduced Ihh expression, and in vivo chromatin immunoprecipitation demonstrates a direct interaction between the beta-catenin/Lef1 complex and the Ihh promoter.

Animals↗
PubMed1999

Nurr1, an orphan nuclear receptor, is a transcriptional activator of endogenous tyrosine hydroxylase in neural progenitor cells derived from the adult brain.

Adult rat-derived hippocampal progenitor cells express many of the molecules implicated in midbrain dopaminergic determination, including FGF receptors 1, 2 and 3, the sonic hedgehog receptor components Smo and Ptc, and the region-specific transcription factors Ptx3 and Nurr1. Here we use undifferentiated progenitors to probe the events leading to the dopaminergic phenotype and find that the influences of Nurr1 can be temporally and mechanistically uncoupled from the patterning influences of sonic hedgehog and FGF-8 or the more generic process of neuronal differentiation itself. In gain-of-function experiments, Nurr1 is able to activate transcription of the tyrosine hydroxylase gene by binding a response element within a region of the tyrosine hydroxylase promoter necessary for midbrain-specific expression. This activation is mediated through a retinoid X receptor independent mechanism and occurs in all precursors, regardless of differentiation status. Overexpression of Nurr1 does not affect proliferation or stimulate neuronal differentiation and has no influence on the expression of other dopaminergic markers. This uncoupling of tyrosine hydroxylase expression from other dopaminergic markers suggests that the midbrain dopaminergic identity is dictated by a combination of pan-dopaminergic (e.g., Shh/FGF-8) and region-specific (Nurr1) mechanisms.

Age Factors↗
PubMed2000

Induction of inner ear fate by FGF3.

Loss-of-function experiments in avians and mammals have provided conflicting results on the capacity of fibroblast growth factor 3 (FGF3) to act as a secreted growth factor responsible for induction and morphogenesis of the vertebrate inner ear. Using a novel technique for gene transfer into chicken embryos, we have readdressed the role of FGF3 during inner ear development in avians. We find that ectopic expression of FGF3 results in the formation of ectopic placodes which express otic marker genes. The ectopically induced placodes form vesicles which show the characteristic gene expression pattern of a developing inner ear. Ectopic expression of FGF3 also influences the formation of the normal orthotopic inner ear, whereas another member of the FGF family, FGF2, shows no effects on inner ear induction. These results demonstrate that a single gene can induce inner ear fate and reveal an unexpectedly widespread competence of the surface ectoderm to form sensory placodes in higher vertebrates.

Animals↗
PubMed2000

Hes1 is a negative regulator of inner ear hair cell differentiation.

Hair cell fate determination in the inner ear has been shown to be controlled by specific genes. Recent loss-of-function and gain-of-function experiments have demonstrated that Math1, a mouse homolog of the Drosophila gene atonal, is essential for the production of hair cells. To identify genes that may interact with Math1 and inhibit hair cell differentiation, we have focused on Hes1, a mammalian hairy and enhancer of split homolog, which is a negative regulator of neurogenesis. We report here that targeted deletion of Hes1 leads to formation of supernumerary hair cells in the cochlea and utricle of the inner ear. RT-PCR analysis shows that Hes1 is expressed in inner ear during hair cell differentiation and its expression is maintained in adulthood. In situ hybridization with late embryonic inner ear tissue reveals that Hes1 is expressed in supporting cells, but not hair cells, of the vestibular sensory epithelium. In the cochlea, Hes1 is selectively expressed in the greater epithelial ridge and lesser epithelial ridge regions which are adjacent to inner and outer hair cells. Co-transfection experiments in postnatal rat explant cultures show that overexpression of Hes1 prevents hair cell differentiation induced by Math1. Therefore Hes1 can negatively regulate hair cell differentiation by antagonizing Math1. These results suggest that a balance between Math1 and negative regulators such as Hes1 is crucial for the production of an appropriate number of inner ear hair cells.

Animals↗
PubMed2000

The Phox2b transcription factor coordinately regulates neuronal cell cycle exit and identity.

In the vertebrate neural tube, cell cycle exit of neuronal progenitors is accompanied by the expression of transcription factors that define their generic and sub-type specific properties, but how the regulation of cell cycle withdrawal intersects with that of cell fate determination is poorly understood. Here we show by both loss- and gain-of-function experiments that the neuronal-subtype-specific homeodomain transcription factor Phox2b drives progenitor cells to become post-mitotic. In the absence of Phox2b, post-mitotic neuronal precursors are not generated in proper numbers. Conversely, forced expression of Phox2b in the embryonic chick spinal cord drives ventricular zone progenitors to become post-mitotic neurons and to relocate to the mantle layer. In the neurons thus generated, ectopic expression of Phox2b is sufficient to initiate a programme of motor neuronal differentiation characterised by expression of Islet1 and of the cholinergic transmitter phenotype, in line with our previous results showing that Phox2b is an essential determinant of cranial motor neurons. These results suggest that Phox2b coordinates quantitative and qualitative aspects of neurogenesis, thus ensuring that neurons of the correct phenotype are generated in proper numbers at the appropriate times and locations.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Isolation and characterization of a downstream target of Pax6 in the mammalian retinal primordium.

The transcription factor Pax6 is required for eye morphogenesis in humans, mice and insects, and can induce ectopic eye formation in vertebrate and invertebrate organisms. Although the role of Pax6 has intensively been studied, only a limited number of genes have been identified that depend on Pax6 activity for their expression in the mammalian visual system. Using a large-scale in situ hybridization screen approach, we have identified a novel gene expressed in the mouse optic vesicle. This gene, Necab, encodes a putative cytoplasmic Ca(2+)-binding protein and coincides with Pax6 expression pattern in the neural ectoderm of the optic vesicle and in the forebrain pretectum. Remarkably, Necab expression is absent in both structures in Pax6 mutant embryos. By contrast, the optic vesicle-expressed homeobox genes Rx, Six3, Otx2 and Lhx2 do not exhibit an altered expression pattern. Using gain-of-function experiments, we show that Pax6 can induce ectopic expression of Necab, suggesting that Necab is a direct or indirect transcriptional target of Pax6. In addition, we have found that Necab misexpression can induce ectopic expression of the homeobox gene Chx10, a transcription factor implicated in retina development. Taken together, our results provide evidence that Necab is genetically downstream of Pax6 and that it is a part of a signal transduction pathway in retina development.

Amino Acid Sequence↗
PubMed2001

BMP controls proximodistal outgrowth, via induction of the apical ectodermal ridge, and dorsoventral patterning in the vertebrate limb.

Dorsoventral (DV) patterning of the vertebrate limb requires the function of the transcription factor Engrailed 1 (EN1) in the ventral ectoderm. EN1 restricts, to the dorsal half of the limb, the expression of the two genes known to specify dorsal pattern. Limb growth along the proximodistal (PD) axis is controlled by the apical ectodermal ridge (AER), a specialized epithelium that forms at the distal junction between dorsal and ventral ectoderm. Using retroviral-mediated misexpression of the bone morphogenetic protein (BMP) antagonist Noggin or an activated form of the BMP receptor in the chick limb, we demonstrate that BMP plays a key role in both DV patterning and AER induction. Thus, the DV and PD axes are linked by a common signal. Loss and gain of BMP function experiments show that BMP signaling is both necessary and sufficient to regulate EN1 expression, and consequently DV patterning. Our results also indicate that BMPs are required during induction of the AER. Manipulation of BMP signaling results in either disruptions in the endogenous AER, leading to absent or severely truncated limbs or the formation of ectopic AERs that can direct outgrowth. Moreover, BMP controls the expression of the MSX transcription factors, and our results suggest that MSX acts downstream of BMP in AER induction. We propose that the BMP signal bifurcates at the level of EN1 and MSX to mediate differentially DV patterning and AER induction, respectively.

Animals↗
PubMed2002

Delta-Notch signaling induces hypochord development in zebrafish.

Different cell types that occupy the midline of vertebrate embryos originate within the Spemann-Mangold or gastrula organizer. One such cell type is hypochord, which lies ventral to notochord in anamniote embryos. We show that hypochord precursors arise from the lateral edges of the organizer in zebrafish. During gastrulation, hypochord precursors are closely associated with no tail-expressing midline precursors and paraxial mesoderm, which expresses deltaC and deltaD. Loss-of-function experiments revealed that deltaC and deltaD were required for her4 expression in presumptive hypochord precursors and for hypochord development. Conversely, ectopic, unregulated Notch activity blocked no tail expression and promoted her4 expression. We propose that Delta signaling from paraxial mesoderm diversifies midline cell fate by inducing a subset of neighboring midline precursors to develop as hypochord, rather than as notochord.

Animals↗
PubMed2002

The role of bone morphogenetic proteins in the differentiation of the ventral optic cup.

The ventral region of the chick embryo optic cup undergoes a complex process of differentiation leading to the formation of four different structures: the neural retina, the retinal pigment epithelium (RPE), the optic disk/optic stalk, and the pecten oculi. Signaling molecules such as retinoic acid and sonic hedgehog have been implicated in the regulation of these phenomena. We have now investigated whether the bone morphogenetic proteins (BMPs) also regulate ventral optic cup development. Loss-of-function experiments were carried out in chick embryos in ovo, by intraocular overexpression of noggin, a protein that binds several BMPs and prevents their interactions with their cognate cell surface receptors. At optic vesicle stages of development, this treatment resulted in microphthalmia with concomitant disruption of the developing neural retina, RPE and lens. At optic cup stages, however, noggin overexpression caused colobomas, pecten agenesis, replacement of the ventral RPE by neuroepithelium-like tissue, and ectopic expression of optic stalk markers in the region of the ventral retina and RPE. This was frequently accompanied by abnormal growth of ganglion cell axons, which failed to enter the optic nerve. The data suggest that endogenous BMPs have significant effects on the development of ventral optic cup structures.

Animals↗
PubMed2002

Six3 inactivation reveals its essential role for the formation and patterning of the vertebrate eye.

The establishment of retinal identity and the subsequent patterning of the optic vesicle are the key steps in early vertebrate eye development. To date little is known about the nature and interaction of the genes controlling these steps. So far few genes have been identified that, when over-expressed, can initiate ectopic eye formation. Of note is Six3, which is expressed exclusively in the anterior neural plate. However, 'loss of function' analysis has not been reported. Using medaka fish, we show that vertebrate Six3 is necessary for patterning of the anterior neuroectoderm including the retina anlage. Inactivation of Six3 function by morpholino knock-down results in the lack of forebrain and eyes. Corroborated by gain-of-function experiments, graded interference reveals an additional role of Six3 in the proximodistal patterning of the optic vesicle. During both processes of vertebrate eye formation, Six3 cooperates with Pax6.

Animals↗
PubMed2002

Endogenous bone morphogenetic proteins regulate outgrowth and epithelial survival during avian lip fusion.

Our expression studies of bone morphogenetic proteins (BMPs) and Noggin (a BMP antagonist) in the embryonic chicken face suggested that BMP signals were important for closure of the upper lip or primary palate. We noted that Noggin expression was restricted to the frontonasal mass epithelium but was reduced at the corners of the frontonasal mass (globular processes) just prior to fusion with the adjacent maxillary prominences. We therefore performed gain- and loss-of-function experiments to determine the role of BMPs in lip formation. Noggin treatment led to reduced proliferation and outgrowth of the frontonasal mass and maxillary prominences and ultimately to the deletion of the maxillary and palatine bones. The temporary block in BMP signalling in the mesenchyme also promoted epithelial survival. Noggin treatment also upregulated expression of endogenous BMPs, therefore we investigated whether increasing BMP levels would lead to the same phenotype. A BMP2 bead was implanted into the globular process and a similar phenotype to that produced by Noggin resulted. However, instead of a decrease in proliferation, defects were caused by increased programmed cell death, first in the epithelium and then in the mesenchyme. Programmed cell death was induced primarily in the lateral frontonasal mass with very little cell death medial to the bead. The asymmetric cell death pattern was correlated with a rapid induction of Noggin in the same embryos, with transcripts complementary to the regions with increased cell death. We have demonstrated a requirement for endogenous BMP in the proliferation of facial mesenchyme and that mesenchymal signals promote either survival or thinning of the epithelium. We furthermore demonstrated in vivo that BMP homeostasis is regulated by increasing expression of ligand or antagonist and that such mechanisms may help to protect the embryo from changes in growth factor levels during development or after exposure to teratogens.

Animals↗
PubMed2002

Notch1 is required for neuronal and glial differentiation in the cerebellum.

The mechanisms that guide progenitor cell fate and differentiation in the vertebrate central nervous system (CNS) are poorly understood. Gain-of-function experiments suggest that Notch signaling is involved in the early stages of mammalian neurogenesis. On the basis of the expression of Notch1 by putative progenitor cells of the vertebrate CNS, we have addressed directly the role of Notch1 in the development of the mammalian brain. Using conditional gene ablation, we show that loss of Notch1 results in premature onset of neurogenesis by neuroepithelial cells of the midbrain-hindbrain region of the neural tube. Notch1-deficient cells do not complete differentiation but are eliminated by apoptosis, resulting in a reduced number of neurons in the adult cerebellum. We have also analyzed the effects of Notch1 ablation on gliogenesis in vivo. Our results show that Notch1 is required for both neuron and glia formation and modulates the onset of neurogenesis within the cerebellar neuroepithelium.

Animals↗
PubMed2002

Spiel-ohne-grenzen/pou2 mediates regional competence to respond to Fgf8 during zebrafish early neural development.

Neural patterning of the vertebrate brain starts within the ectoderm during gastrulation and requires the activity of organizer cell populations in the neurectoderm. One such organizer is located at the prospective midbrain-hindbrain boundary (MHB) and controls development of the midbrain and the anterior hindbrain via the secreted signaling molecule Fgf8. However, little is known about how the ability of neural precursors to respond to Fgf8 is regulated. We have studied the function of the zebrafish spiel-ohne-grenzen (spg) gene in early neural development. Genetic mapping and molecular characterization presented in the accompanying paper revealed that spg mutations disrupt the pou2 gene, which encodes a POU domain transcription factor that is specifically expressed in the MHB primordium, and is orthologous to mammalian Oct3/Oct4. We show that embryos homozygous for spg/pou2 have severe defects in development of the midbrain and hindbrain primordium. Key molecules that function in the formation of the MHB, such as pax2.1, spry4, wnt1, her5, eng2 and eng3, and in hindbrain development, such as krox20, gbx2, fkd3 and pou2, are all abnormal in spg mutant embryos. By contrast, regional definition of the future MHB in the neuroectoderm by complementary expression of otx2 and gbx1, before the establishment of the complex regulatory cascade at the MHB, is normal in spg embryos. Moreover, the Fgf8 and Wnt1 signaling pathways are activated normally at the MHB but become dependent on spg towards the end of gastrulation. Therefore, spg plays a crucial role both in establishing and in maintaining development of the MHB primordium. Transplantation chimeras show that normal spg function is required within the neuroectoderm but not the endomesoderm. Importantly, gain-of-function experiments by mRNA injection of fgf8 and pou2 or Fgf8 bead implantations, as well as analysis of spg-ace double mutants show that spg embryos are insensitive to Fgf8, although Fgf receptor expression and activity of the downstream MAP kinase signaling pathway appear intact. We suggest that spg/pou2 is a transcription factor that mediates regional competence to respond to Fgf8 signaling.

Animals↗
PubMed1992

THE CHLOROPLAST H+-ATPase: PARTIAL REACTIONS OF THE PROTON.

This article reviews proton intake, charge transfer and proton release by F-ATPases, based in part on flash spectrophotometric studies on the chloroplast ATPase in thylakoid membranes, CF1Fo. The synthesis-coupled translocation of charges by CF1Fo (maximum rate <1500 s-1) and the dissipative flow through its exposed channel portion, CFo (rate >10 000 s-1), are extremely proton-specific (selectivity H+:K+>10(7):1). The proton-specific filter is located in CFo. Proton flow through exposed CFo can be throttled by adding subunit (&dgr;) or subunit &bgr; of CF1. These subunits thus may provide energy-transducing contacts between CF1 and CFo. Recently, we characterized two conditions where, in contrast to the above situation, proton intake by CF1Fo was decoupled from proton transfer across the main dielectric barrier: (a) CF1Fo structurally distorted by low ionic strength transiently trapped protons in a highly cooperative manner, but remained proton tight. This result has been interpreted in terms of Mitchell's proton well. (b) In the absence of nucleotides there is a proton slip. Addition of nucleotides (100 nmol l-1 ADP) abolished proton conduction but not proton intake by CF1Fo. These experiments functionally tag proton binding groups on CF1Fo that are located before the main dielectric barrier.

Journal Article↗
PubMed1992

Effects of 1-[(2-thiazolin-2-yl)amino]acetyl-4-(1,3-dithiol 2-ylidene)-2,3,4,5-tetrahydro-1H-1-benzazepin-3,5-dione hydrochloride (KF-14363) on liver regeneration and function of hepatic mitochondria in partially hepatectomized rats.

Effects of 1-[(2-Thiazolin-2-yl)amino]acetyl-4-(1,3-dithiol 2-ylidene)-2,3,4,5-tetrahydro-1H-1-benzazepin-3,5-dione hydrochloride (KF-14363), a hepatoprotective compound, on liver regeneration, liver nucleic acid levels, mitochondrial respiration activity and hepatic energy metabolism after partial hepatectomy (OPE) in rats were studied. The liver regeneration rate was significantly increased in rats administered 100 mg/kg of KF-14363 for 6 d as compared with the control group administered vehicle. The serum glucose level in rats administered 100 mg/kg of KF-14363 measured 3 h after OPE (OPE 3 h) was significantly higher than that in rats administered vehicle (group A) and the serum insulin level in the KF-14363 group was more than double that of group A. KF-14363 also significantly increased liver nucleic acid levels in OPE rats. In mitochondrial function experiments, KF-14363 (100 mg/kg) was orally administered 2 h after OPE. Three hours after OPE (1 h after KF-14363 administration), state 3 respiration was significantly higher in the OPE 3 h + KF-14363 group than in the OPE 3 h + water group. The adenosine diphosphate/oxygen (ADP/O) ratio was also significantly higher in the OPE 22 h (22 h after OPE) + KF-14363 group than in the OPE 22 h + water group. On hepatic energy metabolism, KF-14363 increased adenosine diphosphate and triphosphate levels. Total adenine nucleotide level in the OPE 3 h + KF-14363 group was significantly higher than that in the OPE 3 h + water group. Adenylate energy charge (AEC) was slightly decreased in the OPE 3 h + water group and significantly decreased in the OPE 22 h + water group than in the corresponding sham group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Synthesis and affinities for dopamine (D2) and 5-hydroxytryptamine (5-HT2A) receptors of 1-(benzoylpropyl)-4-(1-oxocycloalkyl-2-ethyl)-piperazines as cyclic butyrophenone derivatives.

Starting from benzo- or thienocycloalkaneacetic acids, we have prepared a series of 1-(3-p-fluorobenzoylpropyl)-4-(1-oxo-benzo- or thienocycloalkyl-2-ethyl)piperazines 8a-e containing both semirigid and linear butyrophenones pharmacophores. The affinities of these compounds for dopamine (D2) and 5-hydroxytryptamine (5-HT2A) receptors were evaluated in vitro in receptor-binding assays and in functional experiments. The ratios of pKi's for 5-HT2A/D2 receptors may be useful for rapid screening of new compounds and assessing potential induction of extrapyramidal symptoms; ratio values > or = 1.12 (Meltzer's ratio) are predictive of an atypical antipsychotic profile. The new molecules had a ratio in the range of 0.96-1.11 while haloperidol showed a ratio of 0.93. The 2-piperazinoethyl thiotetralone derivative 8d (QF 0506B) with a ratio of 1.11 was the most active compound.

Animals↗
PubMed1991

Tracheal relaxing effects and beta 2-selectivity of TA-2005, a newly developed bronchodilating agent, in isolated guinea pig tissues.

Tracheal relaxing effects and beta 2-selectivity of TA-2005 were investigated by functional experiments and radioligand binding assay in guinea pigs in comparison with those of other beta-agonists, isoproterenol, procaterol, formoterol and salbutamol. The relaxing activity of TA-2005 on histamine-induced contraction in the isolated trachea was most potent among the five agonists, and it was blocked by a beta 2-selective antagonist (ICI 118,551) but not by a beta 1-selective antagonist (bisoprolol). The potency of the relaxing effect was in the order of TA-2005 (pD2 = 9.79) greater than formoterol greater than procaterol greater than isoproterenol greater than or equal to salbutamol. The positive chronotropic effect of TA-2005 was similar to that of isoproterenol; and it was more potent than those of formoterol, procaterol and salbutamol in the isolated atria. The selectivity for tracheal muscle to atria of these agonists were in the order of procaterol greater than greater than or equal to formoterol greater than TA-2005 greater than salbutamol much greater than isoproterenol. A radioligand binding experiment using guinea pig lung and cardiac ventricle as beta 2- and beta 1-adrenoceptor sources, respectively, has also demonstrated that TA-2005 possesses extremely high affinity (IC50 = 1.04 nM) and selectivity (38-fold) to beta 2-adrenoceptors. By addition of GTP, the competition curve of [125I]iodocyanopindolol shifted rightward, indicating the agonist property. These results confirmed that TA-2005 is a highly beta 2-selective agonist that exerts a potent tracheal relaxing effect.

Adrenergic beta-Agonists↗
PubMed1983

Post-traumatic facial nerve paralysis: three cases of delayed temporal bone exploration with recovery.

No consensus exists today on the management of immediate-onset post-traumatic facial nerve paralysis. Controversy surrounds the timing of surgical intervention and the role of electrophysiologic testing. Three patients are presented who sustained immediate, complete facial paralysis following closed head trauma. They did not have prompt facial nerve decompression. In each case, electroneurography and electromyography showed complete nerve degeneration and denervated muscle. Despite the results of the electrophysiologic tests, all patients underwent late surgical decompression of the nerve: one at 2 1/2 months, one at 3 months, and one as late as 14 months after injury. They all had good recovery of facial function within 6 months of surgery. Early surgical intervention has been advocated in post-traumatic facial nerve paralysis if any benefit is to be gained. It is thought that late surgical intervention is unlikely to yield further improvement in the facial nerve function. Experience with these cases suggests that surgical exploration of the facial nerve is indicated at anytime, as it may be beneficial even in very old injuries. The prognostic value of electroneurography and electromyography in determining facial nerve recovery and in deciding upon facial nerve surgery is questioned.

Adult↗