Regulation of chondrogenesis in the developing inner ear: a role for sonic hedgehog.
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Animals↗
Biomedical subjects
D A Frenz
Publications and source records attributed to D A Frenz.
A survey of television meteorologists about their sources for and understanding of pollen counts.
BACKGROUND: Pollen counts are widely used by television stations in news programming but little is known about the sources for and quality of this information. OBJECTIVE: The purpose of this investigation was to survey television meteorologists about their sources for pollen counts and to assess their general understanding of these data. METHODS: Sixty-seven meteorologists employed by television stations in the nation's 20 largest Designated Market Areas (DMAs) were contacted by telephone. A brief survey was administered verbally and their responses were recorded. RESULTS: Thirty-seven meteorologists indicated that their station used pollen counts in news programming. Most were aware of their station's source for this information and reported that viewers contacted them about the pollen count. Few meteorologists, however, knew the type of instrument that was used to obtain pollen samples they aired and only 10 selected the correct definition of a pollen count from a list of three choices. CONCLUSIONS: Pollen counts are an important element in television news programming that are poorly understood by the meteorologists who present them to the public. Allergists are encouraged to better educate the personnel at stations to which they supply pollen counts.
Data Collection↗
Basilar papilla explants: a model to study hair cell regeneration-repair and protection.
Explants of basilar papillae from 6-7 days posthatch chicks were cultured in growth medium for a period of 1-8 days. Hair cells were counted following staining of stereocilia bundles with FITC-phalloidin, and the percentage of hair cell survival was determined by comparison to control (i.e. uncultured) specimens. Hair cell integrity was evaluated by scanning electron microscopy. Although previous studies have utilized organotypic culture of the basilar papilla to assess cell proliferation and ototoxicity, viability and integrity of hair cells was documented for periods of up to only 2 3 days. Our results demonstrate substantive auditory hair cell viability for a period of 7 days in vitro. We describe a pattern of natural hair cell loss in organotypic culture that progresses along a proximal-distal, abneural-neural gradient, mimicking the pattern of hair cell loss that occurs following ototoxic insult to the chick basilar papilla in vivo and the pattern we observed during a 48-h period of exposure of basilar papilla explants to an ototoxic dose of neomycin. Our results provide an important quantitative step for the use of organotypic culture of the chick basilar papilla as a purposeful model to investigate the process of hair cell regeneration-repair in the avian auditory system.
Animals↗
Role of FGF3 in otic capsule chondrogenesis in vitro: an antisense oligonucleotide approach.
Initiation of otic capsule chondrogenesis depends on interactions between the otocyst and surrounding periotic mesenchyme. We previously reported localization of endogenous basic fibroblast growth factor (FGF2) to the epithelium of the mouse otocyst, and initiation of chondrogenesis in cultured periotic mesenchyme by this epithelial-derived signaling molecule. We now report that FGF3, related to FGF2, can also initiate otic capsule chondrogenesis. We show localization of endogenous FGF3 to the otocyst, and suppression of chondrogenesis by antisense oligonucleotides complementary to different regions of the murine FGF3 gene. Our results support a role for FGF3 in otic capsule formation in situ.
Animals↗
Mammalian auditory hair cell regeneration/repair and protection: a review and future directions.
Regeneration/repair and protection of auditory hair cells and auditory neurons is an exciting, rapidly evolving field. Simultaneous developments in the fields of otobiology and surgical otology have led to new and exciting possibilities in inner ear medicine and surgery; specifically, the treatment or prevention of a variety of types of hearing losses in the foreseeable future. Sensorineural hearing loss in humans is commonly associated with a loss of auditory hair cells. It has been generally accepted that hearing loss resulting from hair cell damage is irreversible because the human ear has been considered to be incapable of regenerating or repairing these sensory elements following severe injury. An organ of Corti explant study has shown that it is possible to initiate the regeneration/repair of mammalian hair cells. In this study, ototoxin-damaged organ of Corti explants from juvenile rats were treated with a combination of retinoic acid (10-8M) and fetal calf serum (10%). TGF-alpha has been identified as a growth factor capable of evoking auditory hair cell regeneration/repair in ototoxin-damaged organ of Corti explants. Preliminary in vitro experiments with juvenile rat organ of Corti explants and in vivo studies in the cochleae of adult guinea pigs indicate that pretreatment followed by continuous treatment of the inner ear with a combination of retinoic acid and TGF-alpha can protect the auditory hair cells from the ototoxic effects of aminoglycosides. Because the integrity of spiral ganglion neurons is also essential for normal auditory function, there is a parallel series of in vitro and in vivo studies of the effects of neurotrophic factors on the survival of auditory neurons and the regeneration of injured neuronal processes. Clinical studies have demonstrated that it is now possible to perform surgeries on the inner ear, i.e., partial or total labyrinthectomies, and maintain hearing. The field of cochlear implantation has also provided insights into both the short- and long-term effects of cochlear fenestration on inner ear function. Administration of growth factors to the inner ears of animals is now possible with the use of implanted catheters and miniature infusion pumps. These advances suggest that localized application of drugs to the human inner ear may be feasible. The aim of this paper has been to provide an overview of advances in the study of the biology of auditory hair cells and auditory neurons, as well as recent relevant surgical advances. Taken together, these advances in otobiology and surgery will, in the future, be combined to devise new and innovative treatments for inner ear disorders.
Adult↗
Interaction of the NH2-terminal domain of fibronectin with heparin. Role of the omega-loops of the type I modules.
Determinants of the interaction of the 29-kDa NH2-terminal domain of fibronectin with heparin were explored by analysis of normal and mutant recombinant NH2-terminal fibronectin fragments produced in an insect cell Baculovirus host vector system. A genomic/cDNA clone was constructed that specified a secretable human fibronectin NH2 fragment. With the use of site-directed mutagenesis a set of 29 kDa fragments was obtained that contained glycine or glutamic acid residues in place of basic residues at various candidate sites for heparin binding in the five type I modules that make up the domain. The recombinant fragment containing the wild type sequence had a nearly normal circular dichroic spectra and a melting profile, as assayed by loss of ellipticity at 228 nm, that was indistinguishable from that of the native fragment obtained by trypsinization of plasma fibronectin. A substantial proportion of the wild type recombinant fragment bound to heparin-Sepharose, where it was eluted at the same NaCl concentration as the native fragment. The wild type fragment was capable of promoting matrix-driven translocation, a morphogenetic effect in artificial extracellular matrices that depends on the interaction of the fibronectin NH2 terminus with heparin-like molecules on the surfaces of particles. Mutant fragments in which arginines predicted to be most exposed in the folded fragment were converted to glycines retained the same affinity for heparin as the wild type fragment. In contrast, a mutant fragment in which the single basic residue (Arg99) in the minor loop ("Omega-loop") of the second type I module was converted to a glycine had an essentially normal melting profile but exhibited no binding to heparin and failed to promote matrix-driven translocation. A mutant fragment in which the single basic residue (Arg52) of the first type I module was converted to a glycine also completely lacked heparin binding activity, but one in which the single basic residue (Arg191) the fourth type I module was converted to a glycine retained the ability to bind heparin. A mutant fragment in which the single basic residue (Lys143) in the Omega-loop of the third type I module was converted to a glutamic acid lacked heparin binding activity but had a CD spectrum similar to the heparin-liganded native protein and was capable of promoting matrix-driven translocation. The results indicate that multiple residues in the Omega-loops of the fibronectin NH2-terminal domain participate in its interactions with heparin. In addition, the conformation of one of the nonbinding mutants may mimic the heparin-induced structural alteration in this fibronectin domain required for certain morphogenetic events.
Amino Acid Sequence↗
Effect of retinoic acid on otic capsule chondrogenesis in high-density culture suggests disruption of epithelial-mesenchymal interactions.
Previous studies have shown that in utero exposure of the mouse embryo to nonphysiological levels of all-trans retinoic acid (RA) produces malformations of the epithelial-derived auditory and vestibular receptors of the inner ear and its surrounding cartilaginous capsule. In this study, we demonstrate the effects of all-trans RA in high-density cultures of the periotic mesenchyme fated to form the otic capsule. Our results demonstrate an inhibition of chondrogenesis in cultured periotic mesenchyme + otic epithelium of embryonic age E10.5 days (E10.5) in response to all-trans RA exposure. However, at later stages of development (i.e., E12, E14), when epithelial-mesenchymal interactions are no longer required for initiation of chondrogenesis, exposure to this teratogen has no effect on the chondrogenic process. Two analogues of all-trans RA, i.e., cis-RA and trans-retinol, were investigated for their biological activity in chondrogenic cultures of inner ear mesenchyme + epithelium. Moreover, we tested the inductive capability and responsiveness of in utero RA-exposed inner ear tissues when cultured with inner ear tissues that were not exposed to this teratogen. Our results support the hypothesis that all-trans RA disrupts otic capsule formation by interfering with the tissue interactions required for its normal differentiation and development.
Animals↗
A comparison of pollen recovery by three models of the Rotorod sampler.
BACKGROUND: During the past 15 years, three models of the Rotorod Sampler have been manufactured for aeroallergen sampling. Although several studies have considered pollen recovery by specific Rotorod models, none explored inter-model sampling differences. OBJECTIVE: The purpose of this present investigation was to compare pollen recovery by three Rotorod models that are widely used by allergists. METHODS: Two Model 85s, two Model 95s, and two Model 40s were installed 1.5 m above the flat rooftop of a surburban 3-story office building. Fifty atmospheric samples collected between June and August 1996 were analyzed according to the standard conventions suggested by the manufacturer. Differences in pollen recovery were evaluated using an analysis of variance followed by Duncan's multiple range test. RESULTS: Pollen counts ranged from 7.4 to 406.8 pollen grains per cubic meter of air. Differences in pollen recovery by the six devices were not statistically significant. CONCLUSIONS: Pollen counts obtained with three models of the Rotorod Sampler were generally similar and could be compared directly. This study demonstrated continuity in the performance of the Rotorod Sampler over successive generations of the device.
Air Pollution↗
Role of BMP-2a in otic capsule chondrogenesis.
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Animals↗
Retinoic acid-induced embryopathy of the mouse inner ear.
Retinoic acid (RA) is an active metabolite of vitamin A that is teratogenic when present in excess during mammalian embryogenesis. We have investigated the effect of embryonic exposure to nonphysiological levels of all-trans RA on the development of the mouse inner ear. Dysmorphogenesis of both vestibular and auditory portions of the inner ear, and abnormal formation of the surrounding capsule are produced by exposure to teratogenic levels of RA at an embryonic age of 9 days (E9). There was no observable teratogenic effect of RA when administered at earlier (i.e., E7 or E8) or later (i.e., E10) stages of otic morphogenesis. We hypothesize that exposure to high levels of RA during a critical period of early otic morphogenesis interferes with the inductive tissue interactions required for inner ear development.
Abnormalities, Drug-Induced↗
A calibration program for Rotorod samplers.
BACKGROUND: Despite widespread use in the United States, the need for calibrating Rotorod Samplers on a regular basis has not been demonstrated. OBJECTIVE: The purpose of this present investigation was to inspect Rotorods that had been operating in the field to determine whether they conformed to the manufacturer's operating specifications. METHODS: Allergists who own Rotorods voluntarily returned their devices to the manufacturer for calibration over the course of two successive winters. The speed of each device's motor was measured with a stroboscopic tachometer. RESULTS: Of the 89 devices examined, ten were found to be operating at the manufacturer's exact speed specification (2400 RPM) and another 31 were within 5%. The remaining devices deviated by more than 5% from the prescribed speed or possessed motors that would not operate. CONCLUSIONS: The authors underscore the importance of calibrating Rotorod Samplers to maintain data quality.
Air↗
Seasonal characteristics of ragweed pollen dispersal in the United States.
BACKGROUND: The most definitive reports concerning the seasonal characteristics of ragweed (Ambrosia spp) pollen dispersal in the United States date back 60 years to work conducted with gravity slide samples. OBJECTIVE: Volumetric pollen data from 23 sampling sites were used to study the ragweed pollen season. METHODS: The date of first and final pollen capture and the date with maximum airborne pollen concentration (the "peak date") were used to compare the pollen seasons at locations ranging from approximately 30 degrees N to 45 degrees N latitude. RESULTS: Sixteen cities located north of 38 degrees N possessed similar peak dates (P = 1), generally achieving maximum airborne pollen concentration in late August or early September. Four cities located south of 38 degrees N experienced later peak dates, with the most southerly city reaching maximum pollen levels in mid-October. Three cities located in the Northwest did not recover ragweed pollen in air samples. CONCLUSION: This study confirms earlier reports and suggests what time of year source avoidance is most critical for ragweed sensitive individuals in various locations.
Allergens↗
Induction of chondrogenesis: requirement for synergistic interaction of basic fibroblast growth factor and transforming growth factor-beta.
Interactions between the epithelial anlage of the developing mouse inner ear and its associated periotic mesenchyme control the differentiation of the cartilaginous otic capsule. Transforming growth factor-beta 1 (TGF-beta 1) is a naturally occurring signal peptide that is present in these tissues at times of active differentiation and morphogenesis. Previous studies have shown that TGF-beta 1 alone is not a sufficient stimulus to initiate chondrogenesis in cultured periotic mesenchyme. In this study, we provide evidence that basic fibroblast growth factor (bFGF) can elicit a specific but limited chondrogenic response in cultured periotic mesenchymal cells. We also demonstrate that simultaneous addition of bFGF and TGF-beta 1 to cultured periotic mesenchyme results in a full chondrogenic response comparable to that which occurs when periotic mesenchyme is grown in the presence of its natural inductor tissue (i.e. otic epithelium). Utilizing antibodies directed against bFGF, we show localization of endogenous bFGF in the otic epithelium in vivo and in mixed epithelial-mesenchymal cultures. Additionally, we demonstrate the presence of FGF-like activity in medium conditioned by otic epithelium. Blocking of epithelial elicited chondrogenesis by a combination of both alpha bFGF and alpha TGF-beta 1 antibodies provides further evidence of the necessity for these growth factors in the chondrogenic differentiation of periotic mesenchyme in vitro. Our results suggest a role for both bFGF and TGF-beta 1 in the regulation of chondrogenesis during otic capsule formation in situ.
Animals↗
Transforming growth factor beta 1 is an epithelial-derived signal peptide that influences otic capsule formation.
Interactions between epithelial and mesenchymal tissues in the developing inner ear direct the formation of its cartilaginous capsule. Recent work indicates that many growth factors are distributed in the early embryo in vivo in a temporal-spatial pattern that correlates with sites of ongoing morphogenetic events. We report here that the localization of transforming growth factor beta 1 (TGF-beta 1) in both epithelial and mesenchymal tissues of the mouse inner ear between 10 and 16 days of embryonic development (E10-E16). In addition, utilizing a high-density culture system as an in vitro model of otic capsule chondrogenesis, we show that modulation of chondrogenesis by TGF-beta 1 in cultured mouse periotic mesenchyme mimics the in vitro effects of otic epithelium on the expression of chondrogenic potential. We provide evidence of a causal relationship of this growth factor to otic capsule formation in situ by demonstrating that the actual sequence of chondrogenic events that occur in the developing embryo is reproduced in culture by the addition of exogenous TGF-beta 1 peptide. Furthermore, in cultures of mesenchyme containing otic epithelium, we demonstrate the localization of endogenous TGF-beta 1, first within the epithelial tissue and later within both the epithelium and its surrounding periotic mesenchyme, contrasted to an absence of endogenous TGF-beta 1 in cultures of mesenchyme alone. Our results suggest that TGF-beta 1 is one of the signal molecules that mediate the effects of otic epithelium in influencing the formation of the cartilaginous otic capsule.
Animals↗
Role of transforming growth factor-beta in chondrogenic pattern formation in the embryonic limb: stimulation of mesenchymal condensation and fibronectin gene expression by exogenenous TGF-beta and evidence for endogenous TGF-beta-like activity.
The possible role of TGF-beta-like molecules in skeletal pattern formation in the embryonic vertebrate limb was studied by analyzing the mechanism of enhancement of chondrogenesis in chick wing bud mesenchyme in vitro and testing for the presence and distribution of endogenous TGF-beta-like activity in this tissue. Transient exposure (3-6 hr) to TGF-beta 1 (1-2 ng/ml) on the day after plating resulted in a 1.5- to 2-fold enhancement of accumulation of Alcian blue (pH 1.0)-stainable extracellular matrix 5 days later. The enhancement of differentiation was preceded by an acceleration and an increase in the extent of precartilage condensation formation, visualized by Hoffman Modulation Contrast microscopy a day after TGF-beta treatment. In contrast, neither condensation nor subsequent chondrogenesis was stimulated by transient treatment with TGF-beta 1 on the day of plating. The effectiveness of a TGF-beta treatment regimen in enhancing chondrogenesis was correlated with its effectiveness in stimulating condensation formation. Exposures to the factor for 3-6 hr on the day after plating, which most consistently stimulated both condensation formation and chondrogenesis, also corresponded to a peak in the enhancement of the steady-state level of fibronectin mRNA (fourfold to eightfold over control levels) measured at the end of the treatment period. The elevation in fibronectin mRNA levels brought about by this treatment persisted throughout the period of condensation. Endogenous TGF-beta-like activity was detected in limb mesenchyme: extracts of freshly isolated and cultured limb tissues contained 6-25 pg TGF-beta-like activity per 1 x 10(6) cells by the Mv1Lu cell proliferation inhibition assay, and indirect immunofluorescence using a polyclonal antibody directed against a TGF-beta-related peptide indicated a patchy distribution of endogenous TGF-beta-like reactivity within a day after culture. These findings are discussed in relation to the "fibronectin prepattern" hypothesis for limb pattern formation.
Animals↗
Epithelial control of periotic mesenchyme chondrogenesis.
Morphogenesis of the cartilaginous otic capsule is directed by interactions between the epithelial anlage of the membranous labyrinth (otocyst) and its associated periotic mesenchyme. Utilizing a developmental series of high-density (micromass) cultures of periotic mesenchyme to model capsule chondrogenesis, we have shown that the early influence of otic epithelium in cultures of 10.5- or 14-gestation day (gd) periotic mesenchyme results in initiation or suppression of chondrogenesis, respectively. Furthermore, we have shown that introduction of otic epithelium at two distinct times during in vitro development to cultures of 10.5-gd mesenchyme cells results first in an initiation and then in an inhibition of their chondrogenic response. These influences of epithelial tissue on chondrogenic differentiation by periotic mesenchyme are not tissue specific but are characterized by temporal selectivity. The ability of otic epithelium to influence chondrogenesis and the competence of the periotic mesenchyme to respond to its signals are dependent upon the developmental stage of both tissues. This study provides conclusive evidence that otic epithelium acts as a developmental "switch" during otic capsule morphogenesis, signaling first the turning on and then the turning off of chondrogenic programs in the responding cephalic mesenchyme.
Animals↗
Transforming growth factor-beta. Paracrine mediator of otic capsule formation.
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Animals↗