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PubMed1995

Effects of exogenous testosterone on sonic muscle mass in the weakfish, Cynoscion regalis.

Three testosterone (T) implant experiments were carried out to investigate the hormonal control of seasonal hypertrophy in the sound producing, or sonic, muscles of the weakfish Cynoscion regalis. The first experiment examined the role of T in the seasonal increase in sonic muscle mass noted in adult male weakfish during the spring and summer spawning period. Specimens held over-winter were implanted with T or vehicle prior to the natural spawning season. The sonic muscle mass of the T-implanted group increased two and a half-fold over a period of 3 weeks, while that of the sham-implanted group did not change. At the end of the experiment, the cross-sectional area of the sonic muscle fibers in the T-implanted group averaged 500 microns 2, while that of the sham-implanted group averaged 300 microns 2. In a second experiment, the elevated sonic muscle mass of spawning male weakfish was sustained with pharmacological levels of plasma T for a period of 4 months following the spawning season. The sonic muscle mass of the sham-implanted group decreased to typical postseason values. In a third experiment, male and female age-0 weakfish were held over-winter and then implanted with T in advance of their first natural spawning season. The sonic muscles of the T-treated male specimens attained twice the mass of those of the sham-implanted male specimens in 3 weeks time. No sonic muscle development was noted in any of the female specimens.

Aging↗
PubMed1993

Sonography with sonicated albumin in the detection of vesicoureteral reflux.

The primary radiological procedures for diagnosing vesicoureteral reflux are fluoroscopic and radionuclide cystography. Ultrasonography, with no ionizing radiation, would be useful as a screening tool for the diagnosis of reflux due to its absence of radiation exposure. We evaluated the usefulness of ultrasonography with sonicated albumin in the diagnosis of vesicoureteral reflux. Sonicated albumin contains approximately 3 to 5 x 10(8) microspheres per ml., which are echogenic. Sonicated albumin was tested in vitro, alone, and in human and porcine urine to assess microsphere stability. Urine dilutions, specific gravity, temperature and pH were used as variables. The mode of delivery was also tested in vitro and in vivo. These studies showed that sonicated albumin microspheres were stable over a wide range of chemical variables and urine composition. Sonicated albumin produced an image of uniform echogenicity when it was pre-loaded into a Foley catheter and followed by saline infusion in vitro. Fluoroscopic cystograms, using standard radiopaque contrast media, in 5 Hanford mini-swine in which unilateral reflux had been created previously confirmed the presence of reflux unilaterally. Sonographic cystograms with various dilutions of sonicated albumin in 0.9% sodium chloride (1:100, 1:250, 1:500, 1:750 and 1:1,000) were performed. At a dilution of 1:100 sonicated albumin produced dramatic echogenicity in the bladder and refluxing ureters during sonographic imaging. The microspheres appeared to be stable for prolonged periods (more than 40 minutes), thus allowing for a careful sonographic assessment of the entire genitourinary tract. Sonicated albumin may be valuable for the sonographic detection of vesicoureteral reflux.

Albumins↗
PubMed2000

Subgingival polishing with a teflon-coated sonic scaler insert in comparison to conventional instruments as assessed on extracted teeth. (I) Residual deposits.

BACKGROUND: Recent studies have shown that endotoxins are located on the periodontally diseased root cementum and not within it. These studies led to the suggestion that the root surface could be treated less aggressively during periodontal therapy. Thus, we designed a teflon-tubed sonic scaler insert for subgingival polishing. It was our objective to assess to which extent this new instrument is capable of removing bacterial deposits in deep pockets in comparison with conventional scaling instruments. METHOD: We compared the extent to which plaque and calculus could be removed with a curette, a conventional sonic and ultrasonic scaler insert, a Per-io-tor insert, and a teflon-tubed sonic scaler insert. 84 teeth requiring extraction had been treated with one of these instruments. After extraction, the teeth were stained with Malachite green, and the following areas were assessed: area lacking plaque and calculus, calculus, and area only covered with plaque. For statistical comparison, nonparametric analyses were carried out. RESULTS: Curettes and conventional ultrasonic and sonic-scaler inserts had more area lacking plaque and calculus (97.5%, 92.2%, 92.1%) than did the Per-io-tor (80.1%) or the teflon-coated sonic scaler insert (84.4%). A similar effectivity sequence was observed for residual soft deposits (curette: 1.9%, ultrasonic scaler: 6.1%, sonic scaler: 5.4%, teflon-coated sonic scaler: 5.1% and Per-io-tor: 9.5%). CONCLUSIONS: The Per-io-tor and the teflon-coated sonic scaler insert seem to be suitable for the removal of soft deposits on the root surface, but not for the removal of calculus.

Adolescent↗
PubMed1996

Regulation of patched by sonic hedgehog in the developing neural tube.

Ventral cell fates in the central nervous system are induced by Sonic hedgehog, a homolog of hedgehog, a secreted Drosophila protein. In the central nervous system, Sonic hedgehog has been identified as the signal inducing floor plate, motor neurons, and dopaminergic neurons. Sonic hedgehog is also involved in the induction of ventral cell type in the developing somites. ptc is a key gene in the Drosophila hedgehog signaling pathway where it is involved in transducing the hedgehog signal and is also a transcriptional target of the signal. PTC, a vertebrate homolog of this Drosophila gene, is genetically downstream of Sonic hedgehog (Shh) in the limb bud. We analyze PTC expression during chicken neural and somite development and find it expressed in all regions of these tissues known to be responsive to Sonic hedgehog signal. As in the limb bud, ectopic expression of Sonic hedgehog leads to ectopic induction of PTC in the neural tube and paraxial mesoderm. This conservation of regulation allows us to use PTC as a marker for Sonic hedgehog response. The pattern of PTC expression suggests that Sonic hedgehog may play an inductive role in more dorsal regions of the neural tube than have been previously demonstrated. Examination of the pattern of PTC expression also suggests that PTC may act in a negative feedback loop to attenuate hedgehog signaling.

Animals↗
PubMed2002

Summary of recent NASA studies of human response to sonic booms.

NASA Langley Research Center has conducted three groups of studies on human response to sonic booms: laboratory, "inhome," and field. The laboratory studies were designed to: (1) quantify loudness and annoyance response to a wide range of shaped sonic boom signatures and (2) assess several noise descriptors as estimators of sonic boom subjective effects. The studies were conducted using a sonic boom simulator capable of generating and playing, with high fidelity, both user-prescribed and recorded boom waveforms to test subjects. Results showed that sonic boom waveform shaping provided substantial reductions in loudness and annoyance and that perceived level was the best estimator of subjective effects. Booms having asymmetrical waveforms were found to be less loud than symmetrical waveforms of equivalent perceived level. Subjective responses to simulated ground-reflected waveforms were fully accounted for by perceived level. The inhome study presented participants with simulated sonic booms played within their normal home environment. The results showed that the equal energy theory of annoyance applied to a variety of multiple sonic boom exposures. The field studies concluded that sonic boom annoyance is greater than that in a conventional aircraft noise environment with the same continuous equivalent noise exposure.

Aircraft↗
PubMed2002

Weakfish sonic muscle: influence of size, temperature and season.

The influence of temperature, size and season on the sounds produced by the sonic muscles of the weakfish Cynoscion regalis are categorized and used to formulate a hypothesis about the mechanism of sound generation by the sonic muscle and swimbladder. Sounds produced by male weakfish occur at the time and location of spawning and have been observed in courtship in captivity. Each call includes a series of 6-10 sound pulses, and each pulse expresses a damped, 2-3 cycle acoustic waveform generated by single simultaneous twitches of the bilateral sonic muscles. The sonic muscles triple in mass during the spawning season, and this hypertrophy is initiated by rising testosterone levels that trigger increases in myofibrillar and sarcoplasmic cross-sectional area of sonic muscle fibers. In response to increasing temperature, sound pressure level (SPL), dominant frequency and repetition rate increase, and pulse duration decreases. Likewise, SPL and pulse duration increase and dominant frequency decreases with fish size. Changes in acoustic parameters with fish size suggest the possibility that drumming sounds act as an 'honest' signal of male fitness during courtship. These parameters also correlate with seasonally increasing sonic muscle mass. We hypothesize that sonic muscle twitch duration rather than the resonant frequency of the swimbladder determines dominant frequency. The brief (3.5 ms), rapidly decaying acoustic pulses reflect a low-Q, broadly tuned resonator, suggesting that dominant frequency is determined by the forced response of the swimbladder to sonic muscle contractions. The changing dominant frequency with temperature in fish of the same size further suggests that frequency is not determined by the natural frequency of the bladder because temperature is unlikely to affect resonance. Finally, dominant frequency correlates with pulse duration (reflecting muscle twitch duration), and the inverse of the period of the second cycle of acoustic energy approximates the recorded frequency. This paper demonstrates for the first time that the dominant frequency of a fish sound produced by a single muscle twitch is apparently determined by the velocity of the muscle twitch rather than the natural frequency of the swimbladder.

Acclimatization↗
PubMed1980

Antioxidant activity of skim milk: effect of sonication.

The antioxidant activity of skim milk was evaluated in a linoleate emulsion system with hemoglobin as a pro-oxidant. Sonication greatly increased the antioxidant activity of skim milk. The antioxidant activity of the casein fraction of milk was increased most by sonication, and this increase was nearly as great as that for skim milk, suggesting that casein was almost totally responsible for the antioxidant effect of sonication. Total sulfhydryl groups of skim milk decreased upon prolonged sonication, probably the result of the heat evolved in the process. Reactive sulfhydryl content was unchanged by sonication. Sonication had no effect on antioxidant activity of beta-lactoglobulin, reduced urease, or reduced ribonuclease, proteins with free sulfhydryl groups. Apparently sulfhydryl groups were not involved in the increased antioxidant activity of sonicated skim milk. Homogenization at 281.5 kg/cm2 did not increase the antioxidant effect of skim milk. Sonication probably disrupted casein micelles, increasing the effective concentration of casein, which could account for the increased antioxidant activity in the system.

Animals↗
PubMed1994

A metastable state of high surface activity produced by sonication of phospholipids.

Sonication of phosphatidylcholine dispersions generates a metastable high energy assembly of molecules, the existence of which is revealed by its conspicuous surface activity. Freshly sonicated liposome dispersions release molecules to the air/water interface at rates sufficient to produce a close-packed monolayer within minutes. In contrast, monolayers at the surface of multilamellar and extruded vesicles take hours to form. The highly surface active species appears within the first few minutes of sonication, long before a major reduction in turbidity occurs, and accumulates over the course of a few hours of sonication. It disappears upon exhaustive sonication, extrusion, addition of extruded vesicles, or, more slowly, simply on standing. Tests for extraneous substances in the lipids before as well as after sonication revealed amounts of degradation products too small to represent the observed surfactant. Direct evidence that the metastable aggregate releases intact phospholipids was provided by a novel procedure to characterize monolayer composition by comparing surface tension with surface potential, both as a function of surface density. Centrifugation and gel filtration chromatography indicate that the surface activity is associated with a particle of diameter larger than a lysophosphatidylcholine micelle but not larger than limit sonicated vesicles. The metastable material appears to be lipid molecules in other than the normal stable vesicular state, perhaps an incompletely closed vesicle, one in which the inner and outer monolayers have not equilibrated, or possibly a micellar form.

Lipid Bilayers↗
PubMed2006

Magnetic resonance-guided focused ultrasound surgery using an enhanced sonication technique in a pig muscle model.

THE PURPOSE OF THIS STUDY: To evaluate the safety and efficacy of an enhanced magnetic resonance-guided focused ultrasound (MRgFUS) emission protocol that results in more extensive treatment by increasing the volume of each focal ablation using the same energy. MATERIALS AND METHODS: Six pigs were treated with an MRgFUS system combined with real-time MR, for imaging and temperature mapping, with 102 "enhanced" and 97 "regular" focal ablations performed on both buttock muscles. Real-time imaging, temperature mapping, and acoustic reflected spectrum data enabled immediate evaluation of the results. MR contrast-enhanced images and pathology examinations were used for confirmation. RESULTS: The location of the ablated volume by "enhanced" sonication is predictable, with a maximum possible shift of 6 mm toward, and 3 mm away, from the transducer. The ablated volume after enhanced sonication was, on average, 1.8 times larger than after a regular sonication of the same energy. Pathology results showed the same thermally induced damage patterns in the enhanced sonications and the regular sonications. CONCLUSION: Accelerated MRgFUS with enhanced sonication is a safe, controllable, and more effective tissue ablative modality than standard sonication. This new technology may significantly reduce the length of tumor ablation procedures. (Isn't the new technology you're talking about MRgFUS? If so, you don't need to repeat it at the end of this sentence.).

Animals↗
PubMed2003

Application of sonication to release DNA from Bacillus cereus for quantitative detection by real-time PCR.

A rapid sonication method for lysis of Gram-positive bacteria was evaluated for use in combination with quantitative real-time polymerase chain reaction (PCR) analyses for detection. Other criteria used for evaluation of lysis were microscopic cell count, colony forming units (cfu), optical density at 600 nm and total yield of DNA measured by PicoGreen fluorescence. The aim of this study was complete disruption of cellular structures and release of DNA without the need for lysing reagents and time-consuming sample preparation. The Gram-positive bacterium Bacillus cereus was used as a model organism for Gram-positive bacteria. It was demonstrated by real-time PCR that maximum yield of DNA was obtained after 3 to 5 min of sonication. The yield of DNA was affected by culture age and the cells from a 4-h-old culture in the exponential phase of growth gave a higher yield of DNA after 5 min of sonication than a 24-h-old culture in the stationary phase of growth. The 4-h-old culture was also more sensitive for lysis caused by heating. The maximum yield of DNA, evaluated by real-time PCR, from a culture of the Gram-negative bacterium Escherichia coli, was obtained after 20 s of sonication. However, the yield of target DNA from E. coli rapidly decreased after 50 s of sonication due to degradation of DNA. Plate counting (cfu), microscopic counting and absorbance at 600 nm showed that the number of viable and structurally intact B. cereus cells decreased rapidly with sonication time, whereas the yield of DNA increased as shown by PicoGreen fluorescence and real-time PCR. The present results indicate that 3-5 min of sonication is sufficient for lysis and release of DNA from samples of Gram-positive bacteria.

Bacillus cereus↗
PubMed1997

The use of sonication for the efficient delivery of plasmid DNA into cells.

PURPOSE: Ultrasonic methods have considerable potential for the introduction of macromolecules into cells. In this paper we demonstrate that, under controlled conditions, application of 20 kHz ultrasound to a suspension of yeast cells facilitates the delivery of plasmid DNA into these cells. METHODS: Aliquots of growing yeast cells (Saccharomyces cerevisae, strain AH22) were suspended in buffer and exposed to 20 kHz ultrasound from a laboratory (probe-type) sonicator in the presence of microgram quantities of plasmid DNA. Efficiency of DNA delivery was scored as the number of cells transformed. RESULTS: Cell transformation was optimal at 30 seconds sonication using an output of 2.0 watts and resulted in a 20 fold enhancement over control values. At extended sonication times, fewer cells showed evidence of transformation because of reduced cell viability. The increased DNA uptake and the decreased cell viability were both attributable to acoustic cavitation events during sonication. The extent of acoustic cavitation was measured and it was found that there was an increase in cavitation events with increased sonication time. Cell viability was shown to be directly related to the number of cavitation events. The effects of sonication on plasmid DNA were investigated and indicated that the structural integrity of plasmid DNA was unaffected by the sonication conditions employed. CONCLUSIONS: Under controlled conditions, ultrasound is an effective means of delivering plasmid DNA into cells. The subsequent expression of DNA molecules in cells depends upon a balance between transient cell damage and cell death.

DNA Damage↗
PubMed1999

Performance of sonication and microfluidization for liquid-liquid emulsification.

The purpose of this research was to evaluate and compare liquid-liquid emulsions (water-in-oil and oil-in-water) prepared using sonication and microfluidization. Liquid-liquid emulsions were characterized on the basis of emulsion droplet size determined using a laser-based particle size analyzer. An ultrasonic-driven benchtop sonicator and an air-driven microfluidizer were used for emulsification. Sonication generated emulsions through ultrasound-driven mechanical vibrations, which caused cavitation. The force associated with implosion of vapor bubbles caused emulsion size reduction and the flow of the bubbles resulted in mixing. An increase in viscosity of the dispersion phase improved the sonicator's emulsification capability, but an increase in the viscosity of the dispersed phase decreased the sonicator's emulsification capability. Although sonication might be comparable to homogenization in terms of emulsification efficiency, homogenization was relatively more effective in emulsifying more viscous solutions. Microfluidization, which used a high pressure to force the fluid into microchannels of a special configuration and initiated emulsification via a combined mechanism of cavitation, shear, and impact, exhibited excellent emulsification efficiency. Of the three methodologies, sonication generated more heat and might be less suitable for emulsion systems involving heat-sensitive materials. Homogenization is in general a more effective liquid-liquid emulsification method. The results derived from this study can serve as a basis for the evaluation of large-scale liquid-liquid emulsification in the microencapsulation process.

Emulsions↗
PubMed2004

Sonication of proteins causes formation of aggregates that resemble amyloid.

Despite the widespread use of sonication in medicine, industry, and research, the effects of sonication on proteins remain poorly characterized. We report that sonication of a range of structurally diverse proteins results in the formation of aggregates that have similarities to amyloid aggregates. The formation of amyloid is associated with, and has been implicated in, causing of a wide range of protein conformational disorders including Alzheimer's disease, Huntington's disease, Parkinson's disease, and prion diseases. The aggregates cause large enhancements in fluorescence of the dye thioflavin T, exhibit green-gold birefringence upon binding the dye Congo red, and cause a red-shift in the absorbance spectrum of Congo red. In addition, circular dichroism reveals that sonication-induced aggregates have high beta-content, and proteins with significant native alpha-helical structure show increased beta-structure in the aggregates. Ultrastructural analysis by electron microscopy reveals a range of morphologies for the sonication-induced aggregates, including fibrils with diameters of 5-20 nm. The addition of preformed aggregates to unsonicated protein solutions results in accelerated and enhanced formation of additional aggregates upon heating. The dye-binding and structural characteristics, as well as the ability of the sonication-induced aggregates to seed the formation of new aggregates are all similar to the properties of amyloid. These results have important implications for the use of sonication in food, biotechnological and medical applications, and for research on protein aggregation and conformational disorders.

Amyloid↗
PubMed1996

Proof of efficacy of different modified sonic scaler inserts used for debridement in furcations--a dummy head trial.

The purpose of this study was to determine the suitability of different scaling instruments for surgical removal of hard and soft bacterial deposits and for the removal of soft accretions only for maintenance treatment within furcations. 12 upper and 12 lower plastic replicated molars, with through-and-through furcations, were instrumented 3 x with 4 different types of instruments: (1) hand instruments; (2) a conventional sonic scaler insert; (3) a set of 3 modified sonic scaler inserts with budded tips and different angulated shafts; (4) a set of 3 sonic scaler inserts with a plastic-coating and different angulated shafts. The plastic replicas were fixed in a dummy head without any replicated soft tissues. In the furcation area, an easily removable surface coating material was applied to the teeth to represent the "plaque" and a second, more stubborn lacquer layer representing "calculus/cementum". Following instrumentation, the following parameters were recorded to assess efficacy; time required for instrumentation, loss of weight, depth of substance removal at the furcation entrance, % of furcation area instrumented, whereby removal of these 2 layers was judged separately. Only minor differences were observed between hand instruments, conventional and budded sonic scaler inserts as to loss of weight, depth of substance loss and area instrumented. The plastic-coated sonic scaler inserts were just as effective in surface layer removal representing "plaque" as the 3 other instruments, but resulted in less loss of weight and less depth of substance removal. In conclusion, the more aggressive hand instruments, the conventional and budded sonic scaler insert, are preferably used for the surgical phase to increased ease of entry into the furcation dome. An effective debridement of the furcation roof seems only possible with an odontoplastic, for which a furcation is fitted to the instrument by means of an intensive instrumentation, thus leading to weight loss and pronounced substance removal. The plastic-coated sonic scaler inserts seems to be a reasonable choice for maintenance treatment within furcation, since this treatment phase is usually restricted to removal of soft bacterial deposits.

Analysis of Variance↗
PubMed1975

Inactivation of viruses and bacteria by ozone, with and without sonication.

Selected organisms with public health significance were placed in a reaction chamber for treatment by ozonation, by ozonation and sonication, by sonication, or by sonication during oxygenation. Vesicular stomatitis virus, encephalomyocarditis virus, GDVII virus, Staphylococcus aureus, Pseudomonas fluorescens, Salmonella typhimurium, enteropathogenic Escherichia coli, Vibrio cholerae, and Shigella flexneri were inactivated by treatment with ozone. When microorganisms were suspended in phosphate-buffered saline, they were inactivated rapidly by treatment with ozone. However, microorganisms suspended in secondary effluent from a wastewater treatment plant required longer contact times with ozone for complete inactivation. Simultaneous treatments by ozonation and sonication reduced the contact time for complete inactivation of microorganisms in secondary effluent. Treatment by sonication alone or sonication and oxygenation did not inactivate microorganisms. Therefore, the simultaneous treatment of microorganisms in secondary effluent with ozone and sonication resulted in a synergistic effect.

Animals↗
PubMed1996

Activity of asynchronous flight muscle from two bee families during sonication (buzzing).

The indirect flight muscles of bees are used to produce a variety of actions in addition to flight, including sonication, which has a higher frequency than flight. We observed the dynamic movement of the scutum during sonication and the transition from tethered flight to sonication. During sonication, the scutum oscillated above its rest position, indicating that the conformation of the structural components of the thorax had been altered. Sonication vibrations of the thorax occurred by deformation of the scutum rather than by opening of the scutal fissure and are smaller than vibrations associated with flight. During tethered flight, the ratio of muscle activity (recorded via electromyograms) between the dorsal longitudinal muscles and the dorsoventral muscles approached 1, but during sonication the ratio was significantly higher (up to 4.0). This increase may cause the dorsal longitudinal muscles to contract further than the dorsoventral muscles and close the scutal fissure during sonication, so limiting the displacement of the wings and 'decoupling' them from the indirect flight muscles.

Animals↗
PubMed1999

Subgingival access and artificial plaque removal by a sonic cleaning device.

A sonic subgingival cleaning device (soniPick Sonic Interdental Plaque Remover) has recently been marketed with three bristle tips varying in size lengths and bundle diameters. The purpose of this study was to evaluate the ability of these bristle tips to remove subgingival artificial plaque deposits in a laboratory method used for toothbrushes. The laboratory method has been modified for testing the sonic device, to simulate the directions for using the product at home. The dimensions (length x bundle width) of three tips tested were: 0.007" x 0.040"; 0.007" x 0.062"; and 0.009" x 0.062". The tips used with the sonic device were placed on the tooth surface at a 20 degrees angle according to directions, and inserted 3 mm under simulated gingivae. The device was turned on and the tip was moved in a maximum 10 mm stroke for 15 seconds with the brushing machine. For control purposes, a flat, multi-tufted, ADA-accepted manual toothbrush (Oral-B P35) was also tested. The manual toothbrush was tested using the standard methods for evaluating toothbrushes, i.e., with the bristle tips placed at the gingival margin, then brushed at a 45 degrees angle at 250 g weight, using 15 mm strokes for 60 seconds. The depth of subgingival deposit removal was recorded as the maximum depth of the artificial plaque deposit removed from the pressure-sensitive paper under the simulated gingivae over anterior- or posterior-shaped teeth. In the assays conducted, the three bristle tips on the sonic device removed artificial plaque deposits under the simulated gingival at depths of 1.9-2.7 mm. The manual toothbrush had a mean subgingival cleaning depth of 0.6 mm. Differences between the three bristle tips used with the sonic device and the manual toothbrush were significant (p < 0.001 ANOVA). In this laboratory assay, all 3 bristle tips provided with the sonic cleaning device maintained access into and subsequent removal of artificial plaque from the subgingival space.

Analysis of Variance↗
PubMed1996

Sonic Hedgehog in feather morphogenesis: induction of mesenchymal condensation and association with cell death.

Sonic hedgehog is involved in vertebrate tissue interactions during development. During early feather development, Sonic hedgehog appears very early in epithelial placodes. During late feather development, Sonic hedgehog expression precedes the development of the marginal plates and is specifically localized in the marginal plate epithelium, which will later undergo cell death. By using retroviral vectors, exogenous Sonic hedgehog overexpression in developing feathers induced enlarged feather buds that have either lost their anterior-posterior polarity or exhibited reverse orientation. The enlarged dermal condensations may be mediated through broader TGF-beta 2 expression and reduced protein kinase C (PKC) expression. Reciprocal mesenchymal interaction is required for the induction and maintenance of Sonic hedgehog in the epithelial placodes. In scaleless mutant, Sonic hedgehog is absent in the apteric region and aberrantly expressed in the mesenchyme of the abnormal feather ridge. These findings suggest that Sonic hedgehog mediates key interactions between the epithelium and mesenchyme during feather morphogenesis.

Animals↗